The aim of this study was to investigate whether maternal age had an effect on the birthweight of singletons delivered from frozen-thawed blastocyst transfer (FBT) cycles. A total of 1203 FBT cycles occurring between July 2011 and June 2021 at a single centre were retrospectively analysed. Based on the maternal age at FBT, the patients were divided into four groups: <30, 30–34, 35−37, and ≥38 years of age. Main outcomes measured included singleton birthweights, preterm births, large-for-gestational-age (LGA) and small-for-gestational-age (SGA) live births among the groups. There was no significant difference in birth weight among the four groups, while the highest birth weight was found in the <30 years group. The incidence of very preterm births and very low birth weights demonstrated an increasing trend with age; on the contrary, the incidence of preterm births, low birth weight (LBW), high birth weight and LGA and SGA live births gradually decreased with increasing age, but these differences were not statistically significant among groups . Although the proportion of females was lower than that of males, the difference was not statistically significant among the groups. After adjusting for possible confounders, maternal age was found to have no effect on adverse neonatal outcomes in the regression analyses (P>0.05). Birthweight in singleton births from FBT was not affected by maternal age. In receCurrently, literature on the association between the birthweight of newborns and maternal age in IVF cycles is limited. Previously published literature has focused on fresh transfer cycles , 9, 14. 22.1This study retrospectively analysed data from patients who underwent FBT at the Gynecological Endocrinology and Assisted Reproduction Center of Peking Union Medical College Hospital between July 2011 to June 2021. The inclusion criteria were as follows: (1) singleton birth and (2) women with one or two frozen-thawed blastocyst transfers. The exclusion criteria were as follows: (1) disappearance of one twin after the third trimester of pregnancy; (2) congenital uterine malformations; (3) history of cancer such as ovarian; (4) medical diseases such as thyroid dysfunction, diabetes, liver disease, and hypertension; (5) pregnancy related disease such as gestational hypertension, preeclampsia, and GDM; (6) chromosomal abnormalities in either the father or mother; (7) oocytes derived from an ovum donation cycle; (8) sperm derived from epididymal puncture or testicular puncture, and (9) preimplantation genetic test cycle. Data from 1203 patients were included. According to maternal age at FBT, the patients were grouped into four groups: <30, 30–34, 35−37, and ≥38 years of age. The requirement for patient consent was waived owing to the retrospective nature of the study. This study was approved by the Ethics Committee of the Peking Union Medical College Hospital.2.2In our centre, two ovulation stimulation regimens are routinely utilized that include gonadotropin-releasing hormone (GnRH) agonist or GnRH antagonist protocols. When more than three follicles were 18 mm in diameter, human chorionic gonadotropin (HCG) was then injected to induce final oocyte maturation. Transvaginal ultrasound oocyte retrieval was performed 38 h following trigger administration. On the day of oocyte retrieval, insemination was performed on the basis of paternal semen quality. On the third day after fertilization, one or two good cleavage embryos were chosen for transfer. All other embryos were continuously cultured to the blastocyst stage with the informed consent of the patients. If blastocysts formed on day 5 (D5) or 6 (D6), they were scored morphologically and cryopreserved. We referred to the Gardner scoring system for blastocyst evaluation criteria . The qua2.3The blastocysts were thawed on the morning of FBT using a sequential dilution solution of sucrose, hatched by laser, and cultured for approximately 2 h until embryo transfer. Endometrial preparation was performed in two different ways. The natural cycle method was used for patients who had regular menstrual cycles with normal ovulation, and HCG was injected for triggering ovulation. In the artificial cycle method, oestradiol valerate  was administered orally on days 2–4 of menstruation, and different starting doses (2–18mg/day) were given for the women on basis of their previous endometrial conditions. When the thickness of the endometrium reached 8 mm, progesterone  was injected intramuscularly for 5 days. On the 6th day, the blastocysts were thawed and transferred. Progesterone vaginal gel 8%  or intramuscularly ingested progesterone were used for luteal support.2.4PTB was defined as delivery occurring at a gestational age ≥28 weeks and <37 weeks. Very PTB referred to gestational age at birth <32 weeks. LBW referred to weight at birth <2500 g and VLBW referred to weight at birth <1500 g, while macrosomia or high birth weight (HBW) was defined as weight at birth ≥4,000 g. SGA infants were infants whose birth weight were below the 10th percentile of the average weight of infants of the same gestational age. LGA infants referred to newborns whose birth weight were above the 90th percentile of the average weight of infants of the same gestational age.2.5Statistical analyses were performed using SPSS software . The comparison of means between groups depended on data distribution. If the data was continuous, it was analysed by one-way analysis of variance (one-way ANOVA). If the data was categorical, it was analysed by chi-square test or Fisher’s exact test. Bonferroni correction was used to adjust for multiple comparisons. A regression model was used to analyse the influence of maternal age on the birth outcomes of newborns. The <30 years old group was designated as the reference group. Results with P<0.05 were considered statistically significant.3Baseline characteristics are presented in Comparisons of neonatal outcomes among the four groups are shown in via intracytoplasmic sperm injection (ICSI), protocols for endometrial preparation, endometrial thickness, quality and quantity of blastocysts transferred, speed of blastocyst development, and sex ratio, there was still no significant statistical difference. Although VLBW and VPTB were also analysed, their incidence was too low, and the data was too sparse to be meaningful.Logistic regression analysis of adverse neonatal outcomes, with mothers <30 years of age as the reference group, revealed that the incidence of PTB, VPTB, LBW, VLBW, SGA, and LGA were similar among the five groups, as presented in 4via ART and natural pregnancies. They found that the incidence of PTB, LBW and SGA increased with maternal age in the spontaneous conception group, whereas adverse neonatal outcomes as mentioned did not increase with increasing maternal age in the ART group (In our study, there were no significant differences in the prevalence of LBW, PTB, SGA, or LGA among the four groups, and the birth weight of singletons derived from FBT did not change with increasing maternal age, similar to previous studies , 21, 24.RT group . MoaddabRT group . HoweverRT group . BarbuscRT group . RecentlRT group . HoweverRT group . TherefoAs far as we know, this is the first study to investigate whether singleton birth weight after FBT is affected by maternal age. In contrast to previous studies, we recorded the number, quality, and developmental speed of the transferred embryos in detail to avoid confounding factors. As maternal age increased, the proportion of women who transferred one blastocyst decreased, and the rate of good embryo transfer also decreased. Since age is a crucial factor that can affect the clinical outcomes of ART, both the oocyte quantity and quality decline with an increase in maternal age , 27. ComFirstly, women of different ages seek ART treatment for different reasons, and those who are young seek ART treatment may have more health problems . In thisSecondly, the women with advanced age treated with ART may have better economic statuses, good exercise habits, healthier lifestyles, and better physical fitness than the younger patients; therefore, they may represent a healthier group. In addition, women with advanced age who undergo ART are more likely to experience age-related infertility, and knowing this they may pay more attention to their health during pregnancy than younger women and actively seek medical help , 9, 20. Additionally, an interesting phenomenon was observed in this study: the birth weight was lowest in the 35-37 years group; the percentage of male infants was also the lowest in this group, although there were no statistical differences. This raises the question of whether the neonatal sex ratio affects birth weight. Some studies had shown that the incidence of LGA was lower in female infants, and male infants were heavier than female infants –31. KaarHowever, there were some limitations in our study. First, due to its retrospective nature of the study, some background information of patients such as their education level and economic conditions could not be obtained. Second, data such as paternal age and BMI could have affected the birth weight of newborns, but these data were missing. Third, the sample size in this study was not large enough, so a large prospective multicentre study could be considered in the future. Nevertheless, we have endeavoured to ensure the accuracy and reliability of the data in this study, and problems encountered in previous studies such as ambiguous ART methods and unclear embryo quality were avoided. We analysed the influence of the number, quality, and developmental speed of blastocysts transferred in detail and reduced the influence of embryo factors. Moreover, we followed a strict selection criterion to reduce the heterogeneity of the subjects. This study carried out the transfer of frozen-thawed blastocysts because we had more experience in blastocyst culture and vitrification. Since 2005, blastocyst culture and vitrification cryopreservation have been carried out at our centre, and the survival rate after resuscitation has reached more than 99% . Moreove5Birth outcomes of singletons derived from FBT cycles are not affected by maternal age. This is of great significance to older patients and clinicians as it enhances patient confidence in ART procedures, such as FBT. However, attention should be paid to the clinical application of these findings because this study only included women who delivered live births through FBT and excluded patients with pregnancy-related complications. Therefore, the influence of maternal age on the weight at birth of infants delivered from FBT still needs to be investigated in future prospective studies.The original contributions presented in the study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author.The studies involving human participants were reviewed and approved by the Ethics Committee of the Peking Union Medical College Hospital. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.XW contributed to the conception and design of the study. XW and YX performed the literature search. TT and WX were involved in statistical analysis. XW, YX, and WX contributed to the interpretation of the results. XW was responsible for manuscript drafting. All authors contributed to the article and approved the submitted version.


ICSI (intracytoplasmic sperm injection) leads to a reduced male-to-female ratio at birth, whereas blastocyst transfer results in an increased male-to-female ratio. However, limited knowledge exists regarding the impact of these factors on the live birth rate for each gender. This study aimed to investigate the influence of patient characteristics and treatment parameters on the live birth rate for each gender, as well as the ultimate male-to-female ratio at birth in frozen-thawed embryo transfer (FET) cycles.This retrospective cohort study involved a total of 28,376 FET cycles and 9,217 subsequent deliveries, spanning from January 2003 to December 2015. The study consisted of two parts. First, logistic regression models were constructed to determine the factors influencing the male-to-female ratio among babies born after FET. Second, we aimed to investigate the mechanisms underlying this sex ratio imbalance by analyzing data from all transfer cycles. Generalized estimated equations were employed to assess the impact of risk factors on rates of male and female live births separately.in vitro fertilization (IVF) . Conversely, blastocyst transfer yielded a higher proportion of male offspring than cleavage-stage embryo transfer . Analysis of all cycles indicated that ICSI resulted in a reduced likelihood of male live birth in comparison to IVF . However, the transfer of blastocysts rather than cleavage-stage embryos not only increased the chance of male live birth  but also facilitated female live birth .ICSI resulted in a lower proportion of male offspring compared to ICSI was associated with a reduction in the male-to-female sex ratio and a lower rate of male live births, while blastocyst transfer was associated with an increased male-to-female sex ratio at birth and a higher rate of male live births. The ratAdditionally, the impact of procedures used in assisted reproduction technology (ART) on the male-to-female ratio cannot be disregarded. As presented in The objective of this study was to analyze the potentially differential impact of various risk factors on live birth rate for each gender in couples undergoing frozen-thawed embryo transfer (FET).This study was approved by the Institutional Review Board of Shanghai Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine (SH9H-2021-T271-1).This retrospective cohort study was conducted at the Department of Assisted Reproduction of Shanghai Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine. The study screened patients who underwent FET treatment between January 2003 and December 2015, ensuring that complete information was available. In the analyses of data on live births, patients who delivered twins of different genders and those with multiple deliveries during the study period were excluded.The IVF/ICSI procedures followed have been described in our previous publications . In brieEndometrial preparation and the FET procedure have previously been described in detail . In brieP-value <0.05, and odds ratio (ORs) and 95% confidence intervals (CIs) were calculated as indicators of statistically significant effects. Data analysis was conducted using the SPSS software package, version 23.0 .Data are presented in the form of % (n/N). Between-groups differences were assessed using the Chi-square test or Fisher’s exact test, whichever was appropriate. Statistical significance was determined by a Factors analyzed in this study included maternal age , maternal BMI , partner age , duration of infertility , previous miscarriages , previous ectopic pregnancy (yes or no), tubal factor infertility (yes or no), PCOS (yes or no), endometriosis (yes or no), male factor infertility (yes or no), treatment year , fertilized method (IVF or ICSI), endometrial preparation for FET , endometrial thickness at transfer , number of embryos transferred , and embryonic stage at transfer (cleavage or blastocyst).2.First, we analyzed the male-to-female ratio among live-born babies. Univariate logistic regression was employed to examine the potential effects of various characteristics on the male-to-female ratio. Multivariate logistic regression analysis, using the conditional backward method, was conducted to identify variables with a significant influence on the male-to-female ratio among offspring, and to calculate adjusted odds ratios (aORs) and 95% confidence intervals (CIs). The significance of the models was assessed based on the −2 log likelihood, and their goodness of fit of models was evaluated using Nagelkerke’s RP < 0.2 in a Chi-square test or Fisher’s exact test) were included in multivariate models. GEE models were evaluated based on the quasi-likelihood under independence model criterion.Second, we investigated the impact of the aforementioned risk factors on live birth rate for each gender across all transfer cycles. Generalized estimated equation (GEE) models were conducted to address the issue of clustered data (multiple cycles for the same woman), and to calculate ORs and 95% CIs. Significant variables  was constructed to calculate aORs and 95% CIs.n = 1,304) and repeated deliveries by the same women (n = 55), a total of 9,217 deliveries were included for assessment of the associations between the risk factors and the male-to-female ratio at birth; these consisted of 5,639 male babies and 5,047 female babies.The results of the subgroup analysis are displayed in This retrospective cohort study not only confirmed previous findings regarding the association between blastocyst transfer and a skew towards male offspring, as well as the tendency for ICSI to result in fewer male offspring, but also expanded upon these findings by analyzing the rate of live births of each gender. The findings revealed that ICSI was linked to a lower rate of male live births, and that blastocyst transfer favored male live births over female live births.Jacobsen et al. analyzed a population of over 800,000 babies born in Denmark between 1980 and 1993, establishing a natural reference point for the male-to-female ratio at birth of approximately 51.2% males –23. In tThe relationship between maternal age and the male-to-female ratio at birth remains controversial. Rueness et al. have reported a positive association between maternal age and male-to-female ratio at birth, attributing this association to an increased risk of miscarriage related to adverse events during pregnancy in female fetuses . ConversOur study identifies a possible mechanism underlying the alteration in sex ratio associated with ICSI –21, 24. in vitro. We found that blastocyst culture in vitro increased the chance of live birth by 70% for male embryos, whereas the increase for female embryos was only 26%. Two potential explanations for this effect can be considered.In line with previous studies , 25–27, P < 0.01) , 60% (124 of 207) were female, while only 40% (83 of 207) were male . A study < 0.01) . One pos < 0.01) –48. Alth < 0.01) , 49, it  < 0.01) . Hence, in vitro environment may have an adverse effect in terms of X chromosome inactivation (XCI), which in turn may impair the development of female embryos. At the appropriate time, XCI is a crucial step in the normal development of female embryos (in vitro culture was associated with higher expression of XIST, a major controller of XCI, compared to in vivo conditions (in vitro culture could potentially disrupt the normal process of implantation and development, and even lead to early embryonic death.Second, there is a possibility that the  embryos . However embryos . In the nditions . InterfeTo the best of our knowledge, this study is the first to explore the influence of risk factors on the live birth rate for each gender, providing new insights into the mechanisms underlying the skewed male-to-female ratio associated with IVF/ICSI and FET. Another key strength of this study lies in the comprehensive exploration of the association between the male-to-female ratio at birth and various factors involved in ART, including the clinical characteristics of infertile couples and treatment interventions, on which is there is little information in the existing literature. Additionally, the relatively large sample size of this study ensures more reliable modeling and reduces potential bias.The major weakness of this study is its retrospective and non-randomized design, which introduces the possibility of unknown confounding factors. In addition, data on known confounders such as adverse environmental exposure and psychological conditions , 16, 17 ICSI was found to be associated with a decreased male-to-female ratio and a lower rate of male live births in FET cycles, while blastocyst transfer was associated with an increased male-to-female ratio at birth and a higher likelihood of male live birth compared to female live birth.The data underlying this article cannot be shared publicly to protect the privacy of individuals included in the study.TD, BL, and ZY conceived and designed this study. TD, JQ, SZ, JL, and DZ participated in data collection. TD, QX, JY, SZ, JL, and DZ analyzed and interpreted the data. QX, TD, XW, JL, and DZ participated in drafting the manuscript. All the authors participated in making revisions to the article, as well as reading and approving the final manuscript.


Maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) above or below recommendations have been associated with increased paediatric health service utilization as well as increased risk of adverse birth outcomes, including small for gestational age (SGA) and preterm birth (PTB). SGA and PTB are associated with numerous adverse health outcomes in the child, including delayed growth, motor and cognitive impairment. Previous research has identified birth weight and gestational age on the causal pathway in the association between maternal pre-pregnancy BMI and child hospital admissions, there are no studies to date to quantify this relationship across other areas of health service utilization, nor the impact of gestational weight gain. This study aimed to assess if SGA or PTB partially explain the association between maternal weight and paediatric health service utilization.The study population consisted of all women who delivered a singleton, live infant in Ontario between 2012 and 2014, and was assembled from data contained in the provincial birth registry. Health service utilization over the first 24 months following birth was examined by linking data from the registry with other provincial health administrative databases housed at ICES. The mediating roles of PTB and SGA were assessed using the Baron-Kenny method and causal mediation analysis.A total of 204,162 infants were included in the analysis of maternal pre-pregnancy BMI and 171,127 infants were included in the GWG analysis. The small magnitude of association between maternal BMI and paediatric health service utilization impacted our ability to estimate the indirect effect of maternal BMI through adverse birth outcomes (adjusted indirect effect = 0.00). 56.7% of the association between below recommended GWG and increased hospitalizations was attributed to PTB, while 6.8% of the association was attributed to SGA.Paediatric hospitalizations may be partially attributable to PTB and SGA in children born to mothers with below-recommended GWG. However, maternal weight also appears to be related to increased paediatric health service utilization independent of PTB and SGA.The online version contains supplementary material available at 10.1186/s12884-023-05744-w. Elevated maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) both below and above the recommended range are associated with adverse birth outcomes, including small for gestational age (SGA) and preterm birth (PTB) , 2. SGA The association between maternal weight and paediatric health outcomes may be partly explained by adverse birth outcomes, such as SGA or PTB. Cameron et al. previously investigated the relationship between maternal pre-pregnancy BMI and child hospital admissions and noted that birth weight and gestational age were on the causal pathway of this relationship . This stwww.bornontario.ca). BORN is a high-quality, comprehensive registry with 100% coverage of all births in Ontario and demonstrated good agreement between the data elements and patient records . We . We 6]. 0 kg/m2) .The outcomes were measures of paediatric health service utilization, including rates of hospitalizations, ED visits, and physician visits  in childa priori and included infant sex, maternal age, maternal smoking status, pre-existing maternal medical conditions , and neighbourhood income quintile. [Potential confounders of the relationship between maternal pre-pregnancy BMI/GWG and infant health service utilization  were ideuintile. .The following mediators were included in the analysis: gestational age < 37 weeks (PTB) and SGA (< 10th percentile), informed by previous research .We first described baseline characteristics of mothers and children using frequency distributions. Rates of health service utilization during the first 24 months of life were calculated separately for each type of health service . The totTo compare rates of infant health service utilization by maternal pre-pregnancy BMI and by GWG, we first reported unadjusted incidence rate ratios (IRRs) for health service utilization across BMI/GWG categories. We then used multivariable regression analysis to adjust for potential confounders. Due to over-dispersion, we used negative binomial regression  in two sThe Baron-Kenny approach was used to identify potential mediation and causal mediation analysis was used to investigate mediation when the Baron-Kenny approach indicated that it was present. The possible mediation of the relationship between maternal pre-pregnancy BMI or GWG and paediatric health service utilization, by PTB and small for gestational age , was assIn this mediation analysis approach, each step must demonstrate a significant relationship (either positive or negative) in order to proceed to the next step . A conseFor mediation relationships that were apparent following the four steps described, SAS PROC CAUSALMED was used to ascertain the total, natural direct, and natural indirect effects to estimate the effect decomposition  and percWe identified 258,833 birth records in BORN from April 1, 2012 to March 31, 2014. Following exclusions   and 21% had GWG in the recommended range.Characteristics of the entire study population are presented in Table Figure The results suggested an increased rate of hospitalizations and ED visits for children born to overweight and obese persons compared to those born to normal weight persons. However, none of the other associations between pre-pregnancy BMI and paediatric health service use were strong enough to meet criteria for continuation to step 2 Table .The results suggested that children born to mothers who were overweight or obese prior to pregnancy had lower rates of SGA Table  relativeResults suggested that children born SGA had an increased rate of hospitalizations and a small decrease in the rate of ED visits compared to children who were not born SGA Table .step 2) limited the potential for a causal mediation interpretation given that the direction of association was opposite to what would be expected for a causal mediator.Steps 1–3 in the adjusted analyses had thus suggested that SGA may partially explain the relationship between maternal weight and paediatric hospitalization. However, the decreased rate of SGA among children born to mothers who were overweight or obese prior to pregnancy :Results suggested an increased rate of hospitalizations for children born to persons with below recommended GWG. Children born to mothers with above recommended GWG had an increased rate of ED visits compared to those born to mothers with recommended GWG. However, all other associations were small or nonsignificant and removed from all subsequent analyses Table .Results suggested that children born to mothers with below recommended GWG had an increased rate of PTB and SGA, compared to children born to mothers with recommended GWG. Children born to mothers with above recommended GWG were not measurable in this model due to a Hessian error, likely attributed to low cell sizes and lack of variation within the matrix. The model for above recommended GWG was unable to achieve an estimate after adjustment for number of iterations and was thus omitted from subsequent analyses Table .Children born preterm and those with SGA had increased rates of hospitalizations Table .As a result of Steps 1–3 in the adjusted analyses, it was suggestive that PTB and SGA may be mediators in the relationship between below recommended GWG and infant hospitalizations.The association of below recommended GWG with increased hospitalizations was diminished and non-significant after controlling for PTB and was diminished after controlling for SGA Table .Casual Mediation Analysis:Causal mediation analyses were completed to assess the roles of SGA and PTB in the association between below recommended GWG and infant hospitalizations Table . As showThe results of the study suggested that PTB and SGA  may be contributing factors to increased hospitalizations in children born to mothers with below recommended GWG. However, the magnitude of association between maternal weight and paediatric health service utilization was relatively small, impacting the ability to estimate the indirect effect of maternal weight through adverse birth outcomes.The results of this study regarding pre-pregnancy BMI are suggestive of inconsistent mediation. When a relationship within the causal pathway has a different direction of association compared to the other effects, it can result in suppression of the total effect . Within PTB and to a lesser extend SGA appeared to partially explain the observed higher rates of child hospitalizations in the first 24 months of life among children born to mothers with below recommended maternal GWG, compared to children born to mothers with recommended GWG, but was not associated with pre-pregnancy BMI. PTB and SGA are associated with longstanding health implications . The resOur findings are consistent with other studies in that children born to overweight or obese mothers have increased health service utilization . ChildreA strength of this study is availability of maternal weight and height information, linked with paediatric health service utilization in a large population, given the scarcity of maternal weight and height in electronic databases. Population-based information from a birth registry augments the generalizability of the findings to other populations with similar characteristics. A key limitation was the high proportion of missing data on maternal pre-pregnancy BMI and GWG. Self reported pre-pregnancy weight should be interpreted with caution given the potential for reporting bias. Additionally, there may be other factors not explored that may explain the relationship between maternal weight and health service utilization, including the impact of maternal metabolic disease, beyond maternal diabetes or hypertension, on the child during in utero development. Finally, GWG is impacted by gestational length, which can be shortened by PTB. Despite the small proportion of preterm births within the cohort, this is an important limitation within this study, given that it may inflate the perceived role of PTB as a mediator in the relationship of maternal GWG to paediatric hospitalizations. Additionally, other biological mechanisms not captured in this study may lead to PTB, and thereby contribute to future health service utilization.In conclusion, PTB may be a contributor to the increased hospitalizations in children born to mothers with below recommended GWG. Increased paediatric health service utilization in children born to mothers who were overweight or living with obesity prior to pregnancy does not appear to be related to SGA or PTB, suggesting that this observed association is due to either maternal weight status alone or due to other unmeasured mediators. These findings are important as they indicate that adverse birth outcomes may mediate the relationship between maternal weight and pediatric health service utilization and warrants further investigation.Below is the link to the electronic supplementary material.Supplementary Material 1


It is found that the average flight departure delay time during solar X-ray events increased by 20.68% (7.67 min) compared to quiet periods. Our analysis also revealed apparent time and latitude dependencies, with flight delays being more serious on the dayside than on the nightside and longer (shorter) delays tending to occur in lower (higher) latitude airports during solar X-ray events. Furthermore, our results suggest that the intensity of solar flares (soft X-ray flux) and the Solar Zenith Angle directly modulate flight departure delay time and delay rate. These results indicate that communication interferences caused by solar flares directly affect flight departure delays. This work expands our conventional understanding of the impacts of solar flares on human society and provides new insights for preventing or coping with flight delays.Solar flares are one of the severest solar activities that have important effects on near-Earth space. Previous studies have shown that flight arrival delays increase as a result of solar flares, but the intrinsic mechanism behind this relationship is still unknown. In this study, we conducted a comprehensive analysis of flight departure delays during 57 solar X-ray events by using a huge amount of flight data (~ 5 × 10 They have significant impacts on the near-Earth space environment and are therefore an important subject of space weather research3. It has been widely recognized that solar flares can adversely affect various systems, including spacecraft operations, high-frequency (HF) radio communications4, GPS/GNSS navigation5, and air traffic control facilities6. With the development of modern science and technology, the impacts of solar flares on human society have been found to be more and more obvious. A solar flare is a sudden and intense release of energy (about 1028–1032 ergs)9 from the sun, which typically occurs within a matter of minutes to a few hours and can emit various forms of electromagnetic radiation, most notably X-rays and extreme ultraviolet10. These radiations can induce a rapid increase in ionization within the Earth's lower ionosphere, specifically the D region12, resulting in a series of ionospheric disturbances that can cause fading or even disruption of HF radio signals, interfering with communication and navigation systems. However aircraft communication must be available throughout the entire flight route to ensure safety13. Therefore, the impact of solar flares on commercial flights cannot be overlooked.Solar flares are among the severest solar phenomena, characterized by the sudden and intense release of electromagnetic energy from the sun14. Similarly, in September 2017, a series of fairly strong solar flares caused periodic impacts on HF radio users globally. The French Civil Aviation authorities reported that an aircraft equipped with non-Controller Pilot Data Link Communications equipment lost HF radio contact for approximately 90 minutes15. Additionally, some researchers found that the number of aviation catastrophes increased on the third day following an X-class solar flare16.There have been sporadic reports of solar flares affecting flight operations. For example, in November 2015, air traffic control radar stations in Sweden experienced disruptions caused by solar flare-associated radio radiations, resulting in delays in Swedish airspace that lasted for nearly an hour18. However, their focus has primarily been on safety concerns, with little attention paid to flight delays, which are a matter of significant interest to many passengers. Previous research has clearly demonstrated that flight delays can lead to significant economic losses and generate a lot of issues20. Therefore, there is a crucial need to investigate the relationship between solar flares and flight delays. Our previous research has suggested that flare-induced magnetospheric-ionospheric disturbances are strongly linked to flight delays21. Nevertheless, what are the distinctive characteristics of flight delays during solar flares? And what is the underlying mechanism that connects flight delays with solar flares? In this research, based on the data of solar flares from GOES satellite and huge amounts (~ 5 × 106) of flight records, the time and latitude dependency of flight delays during solar flares are revealed and the relevant potential explanations are discussed. It should be noted that our investigation on solar flares only takes into account the electromagnetic radiation emitted from the sun, but does not consider the high-energy particles that often accompany them.The impacts of solar flares on the aviation industry have been researched by various international organizations and scholars22or in the relevant literature23. The list of solar X-ray events used in this paper is obtained from NOAA24, while unlisted events are identified by using the SWPC algorithm based on soft X-ray data obtained from the GOES satellites. According to the NOAA Space Weather Scales, solar X-ray events below class M typically do not significantly affect communications and navigation. Therefore, only M-class and X-class solar X-ray events are selected for this analysis. In this work, only independent solar X-ray events, such as the M1.8 class solar X-ray event shown in Fig. 25, and the begin and maximum times of a solar proton event can also be obtained from database26. The end time of a solar proton event is defined as the time at which the proton flux of the GOES satellite drops below 10 pfu.Solar X-ray events are defined by soft X-ray 1–8 Å) fluxes from the GOES satellites, and they can be obtained from the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC). The details for determining the begin, maximum, and end times of an X-ray event can be found on the NOAA website–8 Å fluxThe individual flight data for this study were obtained from Travelsky Mobile Technology Limited, an affiliated company of the Civil Aviation Administration of China. The dataset contains information on operational dates, flight numbers, departure and arrival airports, as well as scheduled and actual departure and arrival times for all commercial flights between January 1st, 2015 and December 30th, 2019. The airports included in the dataset are Shenzhen Baoan International Airport (IATA: SZX) , Guangzhou Baiyun International Airport (IATA: CAN) , Shanghai Pudong International Airport (IATA: PVG) , Shanghai Hongqiao International Airport (IATA: SHA)  and Beijing Capital International Airport (IATA: PEK) . These airports are ideal samples for analyses since they are the five largest hub airports in China, which could statistically guarantee the data homogeneity.28. In addition, our previous study21 has examined the effect of space weather on arrival delays, which can be contrasted with the present work. Thus, the focus of the current analysis is on the departure delay rather than the arrival delay.The present study focuses on the departure delay as the research object, which is defined as the time difference between the actual departure time and the scheduled departure time of a flight. It has been previously demonstrated that there exists a linear correlation between the arrival delay and departure delay.29 was adopted, but with a larger research sample size (~ 5 × 106 records over 5 years). It is worth noting that the selected solar X-ray events were randomly distributed across weekdays and months, thereby minimizing the influence of weekday and season effects on the results21. Nevertheless, the fact that flight delays exhibit a 24-h intrinsic period is one of the most important factors considered in this study21. The “24-h intrinsic period” is that flight delays vary significantly at different moments of the day32. To eliminate such influence, flights departure within the 24-h-period after the onset of the solar X-ray events are defined as the solar X-ray events affected flights, as marked in red (III) and shown in Fig. It is important to note that flight delays exhibit intrinsic characteristics, including being influenced by various contingencies and having inherent periods. Therefore, to accurately determine the impact of solar flares on flight delays, these factors need to be carefully considered. Flight delays are highly complex, nonlinear, and interrelated, so the research samples should be large enough to smear out those various contingencies as much as possible. To eliminate the influence of accidents, a comparative study similar to Mitsokapas et alFor the analysis in this study, a total of 52 solar X-ray events and 5,295,347 individual flight records  were selected from January 1st, 2015 to December 30th, 2019. It should be noted that all the cancelled flights are removed from our dataset for the entire study, since the percentage of such flights  is too small to impact the final results.35. If the increased flight delay time during solar X-ray events is due to solar flares rather than statistical coincidences, the delay time should reveal some distinct features related to solar flares. Identifying such features would facilitate a better understanding of the causal relationship between solar flares and flight delays.Solar flares can have varied effects on Earth, depending on several factors such as the local time , geographical latitude, flare intensity, and Solar Zenith Angle (SZA)21.To comprehensively assess the impacts of solar X-ray events on flight departure delays, it is essential to compute the empirical probability density function (PDF) of flight departure delays based on all individual flight data in all airports, as shown in Fig. 33. Theoretically, the impact of solar flares on the Earth is mainly concentrated in the subsolar point and varies smoothly with the cosine of SZA37. It can be inferred that during solar flares, HF radio absorption will be more prominent in the dayside ionosphere compared to the nightside ionosphere, where little absorption is expected. Consequently, solar flares can severely disrupt communications and navigation on the dayside, while having little effect on the nightside. However, in this study, the longitudinal variations among the airports are minor, which makes it difficult to directly investigate the longitudinal effect of the flare on flight delays. To reveal the longitudinal effect, all the solar X-ray events affected flights were further categorized into two groups based on the onset of the solar X-ray events: the "Dayside Group" included events that began between 06:00 (LT) and 18:00 (LT), and the remaining events comprised the "Nightside Group". It is worth noting that, no matter when solar X-ray events occur, each group covers all flight data for a full 24-h-period, and it was crucial in removing the hourly delay difference introduced by the “24-h intrinsic period”32.The longitudinal effect  is a key factor that affects the Earth's response to solar flaresFigure 36. As the investigated airports are located in similar longitudes but varying in latitudes, they provide an excellent opportunity to examine the latitude effect. Based on their geographical coordinates, the five airports were classified into three categories: the higher latitude airport, PEK; the middle latitude airport, SHA and PVG; and the lower latitude airport, CAN and SZX. It has been known that solar flares tend to have a more pronounced impact on regions closer to the equator, in contrast to higher latitudes, as revealed by previous research39. The adverse effects of solar flares on various communication and navigation systems are generally more severe in lower latitude areas. This feature is expected to result in comparatively longer flight delays in lower latitude airport and shorter delays in higher latitude airport.Finally, it is noteworthy that latitude is also an important factor that controls the effects of solar flares on EarthThe departure delay PDF for three types of airports during both quiet periods and solar X-ray events are illustrated in Fig. 21, which does not change the overall conclusions. Besides, to ensure that there are indeed differences in flight delays, we conducted the two-sample Kolmogorov–Smirnov test on the "quiet periods" and various "solar X-ray event periods" shown in Figs. It is crucial to eliminate various interference factors to obtain statistically valid results on the effect of solar flares on flight delays. Although we have removed the influence of additional major space weather events, such as coronal mass ejections and solar proton events, there may still be some measurable solar effects that could contaminate the "quiet periods" in our analyses. However, these "contaminations" can only underestimate the impact of solar flares on flight delays21. Our findings suggest that departure delays associated with solar X-ray events are also similar to arrival delays. Furthermore, the observed time and latitude dependency of departure delay time strongly implies that there is a causal relationship between solar X-ray events and flight delays, rather than just coincidental effects. To investigate the underlying mechanism that links flight delays and solar flares, we will focus on the intensity of the solar flares and the SZA.Our previous study has indicated that solar flares can have an impact on flight arrival delays, which are highly correlated with magnetospheric-ionospheric disturbances40. The DRAP model36 is often used to estimate flare-associated HF radio absorption, and the Highest Affected Frequency (HAF) is introduced to determine the highest frequency affected by the absorption of 1 dB due to solar X-ray flux41.flux represents the soft X-ray flux and χ is the SZA. The HAF is an empirical formula that can be used to simply evaluate the interferences of HF communication caused by solar flares. Obviously, the higher X-ray flux and the smaller SZA will lead to more significant consequences.The intensity of solar flares, represented by the soft X-ray flux, is a critical factor in determining their effects on Earth. It is known that the flare associated effects on Earth would be more significant if the flux intensity is more intense. Moreover, the effects of solar flares on Earth are not solely dependent on the X-ray flux but also on the SZA. Many researchers have considered the influence of SZA when investigating the impacts of solar flares on human activitiesFigure


Is the season at conception associated with the risk of childhood cerebral palsy?In this cohort study of more than 4 million births from California during 2007 to 2015, winter and spring conceptions had a 10% increased risk of cerebral palsy compared with summer, whereas no consistent differences were found for fall. The associations remained robust after adjustment for maternal individual- and community-level confounders.This study’s results suggest that future etiological research on cerebral palsy should examine the effects of seasonally varying environmental factors. This cohort study evaluates whether the month or season of conception is associated with cerebral palsy occurrence in California. Cerebral palsy (CP) is the most prevalent neuromotor disability in childhood, but for most cases the etiology remains unexplained. Seasonal variation in the conception of CP may provide clues for their potential etiological risk factors that vary across seasons.To evaluate whether the month or season of conception is associated with CP occurrence.This statewide cohort study examined more than 4 million live births that were registered in the California birth records during 2007 to 2015 and were linked to CP diagnostic records (up to year 2021). Statistical analyses were conducted between March 2022 and January 2023.The month and season of conception were estimated based on the child’s date of birth and the length of gestation recorded in the California birth records.CP status was ascertained from the diagnostic records obtained from the Department of Developmental Services in California. Poisson regression was used to estimate the relative risk (RR) and 95% CI for CP according to the month or the season of conception, adjusting for maternal- and neighborhood-level factors. Stratified analyses were conducted by child’s sex and neighborhood social vulnerability measures, and the mediating role of preterm birth was evaluated.Records of 4 468 109 children  and 4697 with CP  were analyzed. Children conceived in winter (January to March) or spring (April to June) were associated with a 9% to 10% increased risk of CP  compared with summer (July to September) conceptions. Analyses for specific months showed similar results with children conceived in January, February, and May being at higher risk of CP. The associations were slightly stronger for mothers who lived in neighborhoods with a high social vulnerability index, but no child sex differences were observed. Only a small portion of the estimated association was mediated through preterm birth.In this cohort study in California, children conceived in winter and spring had a small increase in CP risk. These findings suggest that seasonally varying environmental factors should be considered in the etiological research of CP. However, studies of seasonal variation of CP are limited, with only a small Polish case-control study reporting the increased CP cases from spring births.21 Here, we conducted a statewide cohort study of more than 4 million births from 2007 to 2015 in California to investigate whether CP diagnosis in childhood was associated with the month or season of conception as a marker for seasonally varying exposures that occurred in early gestation. Given the time of birth can be complicated by the length of gestation that has strong influences on CP risk, we assessed the season of conception as our main focus to capture exposure effects in the early pregnancy that shape the susceptibility of fetal brain injury,18 and we evaluated preterm birth as a potential mediating factor.Epidemiological investigation of seasonal patterns of disease can provide clues about the role of seasonally varying environmental risk factors.STROBE) reporting guideline.This cohort study was approved by the official institutional review board at Yale University and the California Committee for the Protection of Human Subjects. This study was exempt from informed consent requirements as there was no contact with the study population. We followed the Strengthening the Reporting of Observational Studies in Epidemiology .24 CP cases registered in the DDS with a birthplace other than California were not eligible for the study. Overall, we identified a total of 4942 CP cases (linkage rate of 93%), with nonlinkages mainly due to missing identifying information.We created a statewide birth cohort that includes 4 652 013 live births registered in the California birth records during 2007 to 2015. We linked this birth cohort to the CP diagnostic records (up to year 2021) maintained by the California Department of Developmental Services (DDS) to ascertain CP cases. The DDS provides service and support to residents in California who have developmental disabilities or conditions (including CP) through 21 statewide regional centers.We excluded birth records with missing information on maternal residential address or the date of last menstrual period, and records (<0.3%) with potential coding errors such as (1) having a length of gestation less than 20 weeks or greater than 50 weeks, and (2) birth weight less than 500 g or greater than 6000 g. The final sample included 4 468 109 live births and 4697 children with CP , spring (April to June), summer (July to September), and fall (October to December).27 Moreover, we obtained the census tract–level social vulnerability index (SVI) created by the US Centers for Disease Control and Prevention (CDC) and linked this measure to our geocoded maternal residential addresses from the birth records. The SVI ranks all census tracts in the US using a percentile ranking on 15 social factors, then the summation of all factors is taken, reordered among census tracts, and calculated to get the total score, where higher value indicates higher risk group.28 Additionally, CDC labels “flagged high vulnerability areas” as census tracts with any of the 15 factors ranked at the 90th percentile or above, and domain-specific high-risk group  based on factors within each domain.28 The SVI data for California were reported for years of 2010 and 2014 that overlapped with our study period. We assigned 2010 SVI data to the birth years 2007 to 2010, and 2014 SVI to birth years 2011 to 2015.We extracted maternal and child sociodemographic characteristics from the birth records and selected potential confounders that may influence pregnancy planning, fertility, and birth rates based on literature.30 to estimate the relative risk (RR) and the model-based 95% CI for CP according to the month or season of conception, using July or summer as the reference groups that were similar to a previous study.10 In the primary model, we adjusted for birth year (continuous), maternal age at delivery , maternal self-reported race and ethnicity , educational attainment , prepregnancy body mass index , smoking during pregnancy (yes or no), the total SVI (continuous), the DDS catchment area ,31 and child’s sex . In sensitivity analyses, we further adjusted for maternal prenatal care (yes or no), source of payment for prenatal care , receipt of the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) benefits (yes or no), and maternal parity . Maternal race and ethnicity were assessed because CP prevalence is known to vary by race and ethnicity subgroups in California. We also performed sensitivity analyses using singleton births to address concerns of higher CP prevalence among multiple births,32 and adjusted for the exact birth year to relax the linearity assumption of using a continuous birth year. As DDS does not provide the age of diagnosis, we conducted a sensitivity analysis by restricting to children with CP who were aged less than 6 years at the DDS services to assess the importance of the duration of study follow-up time.We used a generalized linear model of Poisson regression4 and we conducted stratified analyses by child’s sex to evaluate potential heterogeneity. Moreover, we evaluated the geographical differences by implementing stratifications on birth regions   mediated the overall associations between the season of conception and CP. We used the marginal structural model with inverse probability weighting method embedded in the CMAverse package in R33 to estimate the natural direct and indirect effects treating preterm as a mediator and allowed for potential exposure-mediator interactions.34 We also evaluated the mediating roles of neonatal Apgar score at 5 minutes and maternal preeclampsia in sensitivity analyses. Statistical analyses were conducted in SAS version 9.4 (SAS Institute) and R version 4.1.2.  from March 2022 to January 2023.Furthermore, we investigated whether the results differ by main CP subphenotypes , and the limb involvement  among spastic CP. Preterm birth is a strong risk factor for CP and seasonal variation on preterm deliveries has been reported.In this California cohort, records of 4 468 109 children  and 4697 with CP  were analyzed. Children born to mothers who were identified as African American or Black and Hispanic or Latinx were more likely to have CP, so did children born to mothers who were older at delivery, were overweight or obese, with a lower education level, or smoked during pregnancy. As expected, CP disproportionally affected preterm birth and male children . We estiIn stratified analyses, we estimated that the associations between winter and spring conceptions and CP risk were stronger if mothers resided in high-risk neighborhoods in terms of socioeconomic factors  and racial and ethnic minority status  . The assThe main results were slightly stronger for the spastic CP subtype   and a Scottish cohort (2006-2011).35 Moreover, the Scottish cohort also reported highest risks of intellectual disabilities and learning difficulties among children conceived in winter and the lowest in summer.35 Results for seasonally increased risks may differ in studies that assessed season of conception vs season at birth as these would cover different susceptible windows for exposures in pregnancy.Investigating seasonal variations in disease occurrence can provide clues about etiologically relevant factors. To our knowledge, only a prior case-control study in Poland during years of 1990 to 1999 and 2000 to 2014 has reported a higher CP incidence for spring births.38 In particular, maternal bacterial infections such as chorioamnionitis and urinary tract infections (UTIs) in late pregnancy have been linked to CP in the offspring.41 However, there is little evidence on the seasonal pattern of chorioamnionitis and therefore may contribute little to the seasonal pattern of CP. Instead, warmer weather  has been reported to increase the risk for UTIs among women in a dose-response relationship with a plateau by 35 °C.43 Winter conceptions that have later stages of pregnancy in summer and fall would therefore be susceptible to UTI infections.43 On the other hand, viral infections generally have winter peaks, such as influenza, chicken pox, and rubella.44 However, the prevalence of both chicken pox and rubella is low in the US due to effective vaccination programs.45 Instead, the influenza infection annual peak of December to February in the US46 clearly overlaps with winter conceptions where we found an increased risk of CP. Early gestational exposures to influenza have also been associated with delays in psychomotor development47 and autism12 in the US, but not yet with CP.It is possible that multiple seasonally varying factors contribute to the seasonality of CP. First, maternal infections during pregnancy, especially when accompanied by fever or an increase in cytokines, have been frequently linked to CP given that inflammation may cause fetal brain damage.18 In fact, more than 150 million agricultural pesticide active ingredients are applied every year in California with a major peak application from May to July,48 a period that overlaps with the first or second pregnancy trimesters for conceptions in late winter and spring. In addition, agricultural pesticides were most heavily applied in the central regions of California, where we also observed a stronger effect size of increased risk of CP. Pesticides can evaporate and drift from the point of application and further contaminate indoor environments and expose nearby residents.49 In addition, exposure to air pollution during pregnancy (such as fine particulate matters) can negatively affect neurodevelopment16 and motor function in the offspring.51 Particles have seasonal peaks in late fall and winter with strong seasonal contrasts were seen especially in northern and central regions of California.52 Currently, epidemiological evidence for associations between ambient air pollution and CP is lacking and requires further investigation.Pesticides exposures are prevalent in California, and our previous study conducted in agricultural regions of California reported that maternal first-trimester exposures to pesticide compounds that disrupt the endocrine systems were associated with CP risk.54 but whether the exposure effects also influence fetal brain development has not been well studied and requires further investigation. It is also possible for some protective factors that occur in the summer and the start of pregnancy as an alternative explanation to our findings. One potential protective environmental factor in summer could be the sunlight exposure and its correlated serum vitamin D levels,58 which might play a limited role in the southern regions of California with abundant sunlight exposures throughout the year.59 To our knowledge, no other protective factors have been discussed in previous literature,11 but this possibility cannot be ruled out.Prenatal exposures to extreme temperature, especially for heat exposure effects in late pregnancy, have been linked to adverse birth outcomes,23 We found that mothers living in neighborhoods with higher socioeconomic risk were more strongly affected by season. This may suggest higher rates of infections from crowded housing conditions or higher exposures to seasonal environmental pollutants that disproportionately affect low-income communities.61 Moreover, low individual-level socioeconomic status may limit the risk mitigation behaviors and options that would reduce environmental exposures such as avoiding outdoor activities during hot seasons or periods of high air pollution or pesticide exposures, as well as having access to indoor air conditioning that reduces effects from extremely hot weather.62 Only a weak mediating effect via preterm birth was found and may be due to the fact that a variety of seasonally varying factors contribute to CP but not necessarily to preterm birth.63 We did not find consistent mediating effects for neonatal Apgar scores and maternal preeclampsia.In California, CP is more prevalent among certain racial and ethnic minority and socially at-risk subgroups.This is a large cohort study of 4 million live births in California and our CP cases were ascertained from the DDS records, limiting recall bias and self-selection participation bias. We were able to evaluate subgroup differences by geospatial locations, neighborhood social vulnerability, and adjusted for a range of potential confounders and quantified the potential mediating effect of preterm birth.23 so did cases diagnosed outside of California. However, only a very small portion of such cases would be included among all births, and this misclassification is likely to be nondifferential by season of conception. Because of this underascertainment and the lack of first diagnosed age of CP cases in the DDS, we were unable to directly compute and compare the incidence rate measures. Second, our results might also be affected by the potential misclassification from estimated month of conceptions using last menstrual.64 However, a validation study suggested that the misclassification of gestational week is usually limited to 2 to 4 weeks for most records,66 and it is reassuring that we observed consistent patterns for most of the consecutive months. While family characteristics such as pregnancy planning that may vary by season were not evaluated,67 our study considered a number of individual-level and community-level confounding factors, and we are not aware of other strong confounding factors. Stratified analyses have lower statistical precision and a higher risk for chance errors when analyzing smaller subgroups. The mediation analysis relied on an untestable assumption that there was no uncontrolled confounding between the exposure, the mediator, or the outcome.34 Additionally, the time of conception is a contextual variable that represents various seasonally varying factors, which can have different strengths, directions, and critical windows on the associations with CP risk.Our study also has limitations. First, there is a possibility of outcome misclassification given that CP cases with mild symptoms less in need of services might not be captured by DDS,In this cohort study in California, we found that winter and spring conceptions had a small increased risk of CP. To our knowledge, this was the largest cohort study to date to suggest that seasonally varying factors may contribute to CP occurrence, and the strength of observed associations may also be affected by social vulnerability. While the results should not be used to promote a change in family planning, our findings suggested that future etiological research on CP should investigate the exposure effects from seasonally varying environmental risk factors.


High-voltage electric field measurement technology has certain applications in electric field measurement of power systems, but due to the limitation of its measurement accuracy and bandwidth, it cannot be used for the measurement of lightning-impulse voltage. In order to calibrate the nonlinearity of the MV-level lightning-impulse voltage measurement system, this paper proposes the design and implementation of a high-precision inductive wideband electric field measuring sensor (EFMS). The influence of the metal shell on the electric field distribution was simulated, and the influence of the electric field non-uniformity coefficient was studied. The characteristics of the EFMS were tested, and the results showed that the EFMS can accurately reproduce the waveform of lightning-impulse voltage and power-frequency voltage, with a proportionality coefficient of 0.05664 V/(kV/m). In mostly uniform and extremely non-uniform fields, the nonlinearity of the EFMS for impulse voltage is less than ±0.25%, and the nonlinearity of the EFMS for power-frequency voltage is less than 0.1%. It is shown that the EFMS can be used for the nonlinearity calibration of ultra-high voltage impulse measurement devices. The accuracy of the measurement of lightning-impulse voltage directly affects the evaluation of the insulation withstand ability of electrical equipment and the effectiveness of the insulation distance in transmission lines ,2. With The standard lightning-impulse voltage measurement system, which converts the measured value into national or international standard, is the most accurate impulse voltage measurement method at present. However, the rated voltage of the internationally recognized standard impulse voltage measurement system is generally only 1500 kV ,4,5, whiThe development of a standard measuring device for linear calibration tests becomes more difficult with the increase in the rated voltage of lightning voltage ,11. HighAccording to different principles, an electric field measuring sensor (EFMS) can be divided into two types ,17,18: eElectric field measurement in power systems has a relatively low requirement for measurement error, and the frequency band width of the waveform to be measured is relatively narrow. Due to the limitations of measurement accuracy and bandwidth, the existing electric field measuring device cannot accurately measure lightning-impulse voltage ,22.In order to meet the requirements of measurement accuracy of impulse voltage, in-depth research on sensor structure, material, and signal processing algorithm is needed to improve the measurement accuracy and measurement bandwidth of EFMSes ,24.In order to realize the calibration of nonlinearity of an MV-level impulse voltage measurement system, a high-precision broadband EFMS based on electric field induction is developed in this paper, which is used for measuring power frequency, high-frequency AC, and impulse voltage. Firstly, the measurement principle of the broadband EFMS is analyzed, and a design method of the broadband EFMS based on electric field induction is proposed. Secondly, the influence of the metal shell on the electric field distribution is simulated, and the requirement of the non-uniformity coefficient is put forward. The characteristic test platform of the broadband EFMS is built, and the scaling factor and nonlinearity of the power-frequency electric field and the impulse electric field are obtained by comparison method. Finally, the typical application scenarios of broadband EFMS are studied.Q is the point charge, the XOY plane is where the field source is located, the Z-axis is parallel to the direction of the probe, and the radius of the spherical shell is R.The point charge electric field is used as the field source. In actual measurements, because of the small voltage induced between the spherical shells, spherical probes can be approximated as an equipotential body. As shown in θ, as the angle to the axis in the XOY plane, and point A  at a distance from the origin d(d > R) with a charge amount of Q. We estimate that the spherical shell is an equipotential body. Furthermore, using the mirror principle, a small charge is seen at point B  in the spherical shell, with q = −(R/d)·Q as the mirror image of Q. The other mirror charge is at O, and the charge quantity is q′ = q = −(R/d)·Q. Take any point P outside the sphere with coordinates of , and use the potential at infinity as the reference point to obtain the potential at P, which can be represented by Equations (1)–(3) [ε is the permittivity of space; R is the radius; r is the distance from point O to point P; d is the distance from O to Q; δ, γ, and θ are used to represent the coordinates of any point in a spherical coordinate system. φ1, φ2, and φ3 represent the potentials generated by different charges at point P.We define the center of the probe to be located at the coordinate origin,  (1)–(3) :(1)φ1=Q4a = R/d is the inhomogeneity coefficient, the surface charge density at point P′ , which can be represented using Equations (5) and (6):E0 is the intensity of the electric field at the center of the point to be measured before the sensor is placed.Let P′ represent the intersection point between the line connecting points P and O and the sphere, with P being any arbitrary point. Thus, P′ can be any point located on the sphere. Considering that the electric field on the sphere is solely characterized by its normal component, the electric field intensity at point P′ can be described using Equation (4):Qs on sphere S can be defined as in Equation (7):As shown in d >> R, the probe can be considered under the action of a uniform electric field, and parameter a is infinitely close to zero. Thus, the charge can be obtained from Equation (8):When S can be simplified as Equation (9):Under the uniform electric field, the induced charge on the sphere δ = Δλ = π/2 is obtained from Equation (10), yielding the following:K′ = −3εR2πcosθ, When splitting the sphere into a one-dimensional spherical probe, ΔC is the sampling capacitance.The induced voltage across the probe can be represented by Equation (11):q(t) is the field source and above the Z-axis. The spherical center of the probe is located at the coordinate origin O, as shown in In the actual measurement, the electric field probe cannot be placed in an ideal uniform electric field. The difference in the output voltages between electric field probes in uniform and non-uniform fields is analyzed below. For a spherical, one-dimensional electric field probe in the spherical coordinate system, the point charge q(t) coincides with the probe’s measurement direction, the surface charge density of the probe as a function of time can be derived from the previous section as follows:R is the sphere’s radius, and r and θ are the coordinates in the spherical coordinate system of any point.When the power line of the field source a → 0, that is, R → 0 or d → ∞, the electric field on the probe surface is a nearly uniform field and, from Equation (13), the surface charge density σ1(t) of the probe can be determined:When The total charge of the probe hemisphere under a uniform electric field can be calculated as follows:a ≠ 0, the total charge of the probe hemisphere Q2(t) under the action of a non-uniform electric field can be calculated:When a2 − 2acosθ. According to the integration of Equation (17) term by term, it can be found thatSince Cm represents the sampling capacitance between the upper and lower electrodes of the spherical probe, and the voltage Um(t) at both ends of the capacitor can be represented by Equation (17).Um1(t) can be found using Equations (18) and (19), respectively:In the uniform and non-electric fields, the measured voltages Therefore, if the EFMS with the proportionality coefficient calibrated in the uniform electric field is used in the non-uniform electric field, the deviation of the proportionality coefficient is shown in Equation (20):E0(t) is directly proportional to the induced voltage mU(t) in both uniform and non-uniform fields. However, a difference is present between the proportionality coefficients of uniform and non-uniform electric fields. This difference decreases as the non-uniformity coefficient decreases. When the non-uniformity coefficient a is ≤0.1, the deviation in the proportionality coefficient is less than 1%. Therefore, the EFMS using the proportionality coefficient needs to be calibrated in real time.Based on the above analysis, the measured electric field intensity E0(t) is proportional to the induced voltage mU(t), but there is a deviation in the proportionality coefficient of the EFMS in both uniform and non-uniform fields. With the decrease in the non-uniform coefficient a, the deviation of the proportionality coefficient decreases. When the non-uniform coefficient a ≤ 0.1, the deviation of the proportionality coefficient is less than 1%. Therefore, it is necessary to carry out real-time calibration of the proportionality coefficient of the EFMS.It can be seen from the above analysis that, in both uniform and non-uniform fields, the measured electric field intensity The EFMS was placed in the measured electric field. The induced charge on the spherical shell was then distorted, and the influence of the EFMS on the measured electric field was simulated and studied.Further simulations under various conditions indicate that two methods can reduce the influence of the equipotential spherical shell of the EFMS on the measured electric field. One method is to minimize the volume of the EFMS, but excessively small volume may make it challenging to achieve the measurement function. The other method is to increase the distance between the EFMS and the charges. However, as the distance increases, the intensity of the measured electric field decreases, leading to increased interference.The wideband EFMS comprised an electric field probe, local area network data transmission, and a data reception and processing unit, as shown in To reduce the size of the EFMS, its internal structure adopted a layered modular design. The sampling rate of the A/D converter was either 10 MS/s or 150 MS/s based on the waveform of the measured voltage. The control software for data processing, acquisition, and transmission was developed using C++. Wireless communication was utilized for data transmission, including an internal WLAN module within the sphere and a data reception module on the PC side.The recorded data were displayed on the waveform display interface and then connected to the waveform measurement software for waveform parameter calculations. Additionally, the high-speed acquisition and rapid transmission of large data made reducing the overall system’s power consumption challenging. Therefore, rechargeable lithium batteries with high energy density, strong endurance, and small volume were chosen as the power supply. Due to the small input voltage of the A/D converter, with a maximum range of ±2.5 V, it is necessary to add an attenuator at the front end of the A/D converter. This attenuator scales down the voltage on the sampling capacitor proportionally to adapt to different ranges of electric field intensity measurements. To measure different voltage ranges, the attenuation ratio could be set at 1:1 or 10:1. The schematic diagram of the attenuator is shown in The EFMS was subjected to measurements of the power-frequency electric field in an electromagnetic environment laboratory. First, the spherical electric field probe was positioned at the central location of the electric field source using an insulated support groove. Altering the distance between the upper and lower electrode plates facilitated control over the magnitude of the electric field intensity. A uniform grading ring, similarly designed to that presented in The proportionality coefficient of the EFMS was calibrated using the electric field generator shown in A mostly uniform impulse electric field was constructed using two grading rings, as illustrated in The waveform of the impulse voltage for the EFMS is shown in The nonlinearity of the EFMS was calibrated using a 500 kV standard resistor voltage divider (model RS500) with a nonlinearity less than 0.2%. A 10:1 pre-attenuator was set up. The nonlinearity of the EFMS was calibrated in two environments: mostly uniform field and extremely non-uniform field.For the mostly uniform field, two grading rings with a diameter of 1.5 m were used. The distance between the two electrodes was set to 1 m. The upper electrode was fixed using a crane without the intermediate insulating support rod. The calibration was performed by placing EFMS under the grading rings, approximately 1 m away from them. The calibration voltage ranged from 50 kV to 450 kV. The calibration results are shown in The nonlinearity of the 1800 kV impulse voltage divider was evaluated using the EFMS developed in this study. During the experiment, the distance between the electrodes was 3.2 m, and the applied impulse voltages were 200 kV, 400 kV, 600 kV, 800 kV, 1000 kV, 1200 kV, and 1400 kV. The experimental results were corrected based on the inherent nonlinearity of the EFMS to obtain the nonlinearity results of the 1800 kV divider, as shown in This study aimed to investigate the effectiveness of EFMSes in calibrating the nonlinearity of high-voltage dividers. Our findings revealed the potential of EFMSes as reliable calibration tools in high-voltage measurement applications. In this discussion, we elaborate on these findings, compare them with existing calibration methods, analyze their impact, and propose future research directions.First, our experimental results demonstrated that EFMSes can effectively measure and characterize the nonlinearity of high-voltage dividers. By comparing the readings of EFMSes with the expected voltage values, we observed deviations within an acceptable range for accurate measurements. This indicates that EFMSes hold promise as reliable calibration devices for evaluating the linearity of high-voltage dividers. Notably, EFMSes offer the advantage of not being limited by the measured voltage range, making them versatile tools for calibrating high-voltage dividers of different ranges.Comparing our findings with existing high-voltage divider calibration methods, such as generator voltage ratio comparison, ratio measurements, and laser interferometry, several advantages of EFMSes become evident. First, EFMSes employ a non-contact measurement technique, reducing dependencies on the performance characteristics of the generator. This ensures a more independent and reliable calibration process. Second, EFMSes offer wide bandwidth and high sensitivity, allowing for accurate measurement of dynamic voltage changes and transient behavior. These advantages position EFMSes as viable options for calibrating linearity in high-voltage measurement scenarios.However, it is important to note that several factors can affect the accuracy of calibration results based on EFMSes. One critical factor is the distance between the sensor and the grading ring of the divider, along with sufficiently small non-uniformity coefficients, meaning that the sensor diameter should be significantly smaller than the distance to the grading ring. Additionally, the stability of the sensor’s position and its proximity to other charged objects should be considered. Furthermore, real-time calibration is necessary for each measurement when using EFMSes for calibration. While this requirement adds complexity and time to the calibration process compared to some other methods, it ensures accurate and reliable results.The use of EFMS developed in this paper in a strong electric field will actually cause electric field distortion near the tips of the upper and lower hemispheres, resulting in inaccurate measurement results. Therefore, it is very important to properly position the spherical electric field measuring instrument during the linearity calibration of the high-voltage divider. Generally, the height of voltage dividers exceeding 2 MV is above 8 m. During the measurement process, we increased the distance between the electric field measuring instrument and the grading ring to ensure that the electric field was less than 450 kV/m. From the experimental results, it can be seen that within this range, there will be no sudden change in the output voltage of the electric field measuring instrument. While limiting the electric field value, the electric field measuring instrument will be affected by spatial interference of the electric field.Another limitation of EFMS-based calibration is its sensitivity to corona discharge and surrounding electric field interference. These factors can introduce measurement errors and affect the calibration outcome. Therefore, employing appropriate shielding techniques and keeping the sensor isolated from external electric fields are crucial for achieving accurate calibration results.To address these limitations and explore future research opportunities, we propose the following directions. Firstly, conducting additional experiments covering a wider range of high voltages and different types of high-voltage dividers would help establish the capabilities and limitations of EFMS-based calibration methods more comprehensively. Secondly, further research should focus on developing advanced signal processing techniques and algorithms to enhance the accuracy and precision of EFMS measurements while mitigating the impact of corona discharge and interference.In conclusion, this study showcased the potential of EFMSes as effective tools for calibrating the linearity of high-voltage dividers. The results contribute to the literature by highlighting the advantages of EFMS in high-voltage measurement applications, particularly their versatility across different voltage ranges. Considering the influencing factors and addressing the identified limitations are critical for successful implementation of EFMS-based calibration methods. Future research endeavors should align with the aforementioned research directions to optimize the calibration process and improve overall accuracy and reliability in high-voltage measurements.To accurately evaluate the nonlinearity of a multi-MV impulse voltage measurement device, this paper proposes the development and design of a broadband EFMS. The output voltage of the EFMS is linearly related to the measured electric field, and the influence of the EFMS on the measured electric field is analyzed.To reduce the size, a layered modular design method was used for the internal structure of the EFMS spherical shell to achieve signal processing, analog-to-digital conversion, and data transmission functions. Measurement bandwidth extension techniques and stability improvement methods were studied.An experimental platform for measuring power frequency and impulse voltage was established, and the calibration and nonlinearity test of the EFMS scale factor under power frequency and impulse voltage was conducted. The test results show that the nonlinearity of the EFMS in an impulse electric field is less than ±0.25%, with an electric field ranging from 50 kV/m to 450 kV/m. The nonlinearity of the EFMS is less than 0.1% in a power-frequency electric field, with an electric field ranging from 50 kV/m to 180 kV/m. Finally, the nonlinearity of a 1800 kV impulse divider in an extremely non-uniform field was evaluated using the EFMS. The evaluation results are consistent with the comparison results of a standard impulse voltage divider. Therefore, it is concluded that the developed EFMS can be used for linearity calibration of ultra-high voltage impulse dividers.


In sub-Saharan Africa, the origins of asthma and high prevalence of abnormal lung function remain unclear. In high-income countries (HICs), associations between birth measurements and childhood asthma and lung function highlight the importance of antenatal and early life factors in the aetiology of asthma and abnormal lung function in children. We present here the first study in sub-Saharan Africa to relate birth characteristics to both childhood respiratory symptoms and lung function.Children attending schools in two socioeconomically contrasting but geographically close areas of Nairobi, Kenya, were recruited to a cross-sectional study of childhood asthma and lung function. Questionnaires quantified respiratory symptoms and preterm birth; lung function was measured by spirometry; and parents were invited to bring the child’s immunisation booklet containing records of birth weight and serial weights in the first year.2373 children participated, 52% girls, median age (IQR), 10 years (8–13). Spirometry data were available for 1622. Child immunisation booklets were available for 500 and birth weight and infant weight gain data were available for 323 and 494 children, respectively. In multivariable analyses, preterm birth was associated with the childhood symptoms ‘wheeze in the last 12 months’; OR 1.64, (95% CI 1.03 to 2.62), p=0.038; and ‘trouble breathing’ 3.18 (95% CI 2.27 to 4.45), p<0.001. Birth weight (kg) was associated with forced expiratory volume in 1 s z-score, regression coefficient (β) 0.30 , p=0.008, FVC z-score 0.29 (95% CI 0.08 to 0.51); p=0.008 and restricted spirometry, OR 0.11 (95% CI 0.02 to 0.78), p=0.027.These associations are in keeping with those in HICs and highlight antenatal factors in the aetiology of asthma and lung function abnormalities in sub-Saharan Africa. In high-income countries, the role of antenatal and early life factors in childhood asthma has been highlighted by numerous reports of associations between preterm birth, birth weight, infant weight gain and childhood asthma and lung function.For the first time in a sub-Saharan Africa setting, associations have been identified between birth characteristics and childhood symptoms consistent with asthma, and lung function measured by spirometry.These findings highlight the importance of antenatal factors in the development of asthma and lung function abnormalities in sub-Saharan Africa. Interventions that target the first 1000 days from conception are likely to be important for lifelong respiratory health in sub-Saharan Africa.Asthma is the most common chronic condition of childhood. Although asthma prevalence rates in low-income and middle-income countries (LMICs) are lower than in high-income countries (HICs), it is acknowledged that the morbidity and mortality burden of asthma in LMICs is considerable.5–81) is negatively associated with preterm birth and low birth weight, but positively associated with IWG and the ratio FEV1/forced vital capacity (FVC) is lower in children born preterm, with low birth weight and higher IWG. Whereas meta-analyses and national cohort studies in HICs are numerous and include data from millions of participants,The first 1000 days, from conception to 2 years of age, is a critical window of growth and developmentTupumue (Swahili for ‘let us breathe’) is a cross-sectional observational study in Nairobi, Kenya, comparing the respiratory symptoms and lung function of schoolchildren within the informal settlement of Mukuru with schoolchildren in the nearby more affluent residential area of Buruburu.The methods used in this cross-sectional study are described in detail elsewhere.23Kenya is a lower-middle-income country with a population of 55 million and per capita income of US$1816/year. The national rates of preterm (<37 weeks gestation) and low birth weight (<2500 g) births are 11.5% and 7.6%, respectively.The Tupumue study was codesigned in close co-operation with the two communities of Mukuru and Buruburu, with consultation meetings that included Chiefs, local politicians, parents, children, head teachers, teachers, social workers, counsellors, health workers and representatives from the Ministries of Education and Health.To explain the study to the communities a suite of innovative, inclusive and culturally relevant sensitisation tools using the creative arts was cocreated by academics, arts practitioners, residents and community artists and delivered by local community ‘champions’ to audiences in schools, churches and community venues. All of the fieldworkers were recruited from the two communities.All children aged ≤18 years attending schools in Mukuru or Buruburu were eligible. Participating schools were randomly selected from a sampling frame of all schools. For each chosen school, a class from each year group was randomly selected.23Field workers administered questionnaires to parents/guardians of children aged ≤12 years and to children aged ≥13 years.The questionnaires included:Demographics, school, age, sex, household asset-based wealth score.26Respiratory symptoms.27 28Parental/self-report of whether the study child was born preterm (<37 weeks of pregnancy).Parental/self-report of environmental exposures, for example, exposure to traffic and domestic pollution sources including tobacco use.28The questions asked are included in 10.1136/bmjresp-2023-001895.supp1Supplementary dataParents were invited to bring the study child’s immunisation booklet. This booklet is distributed to all mothers in Kenya at the first contact of a newborn with a healthcare facility, it is used by healthcare providers to document encounters with health services, child immunisations and any illness. The page documenting birth weight and weight measurements made in the first year of life was photographed. Birth weights and serial weights were then entered into the study database.Children performed spirometry using the EasyOn Spirometer  with on-screen incentive software. Nine technicians trained by Education for Health Africa and certified by the Pan African Thoracic Society (PATS) conducted spirometry in accordance with PATS, American Thoracic Society/European Respiratory Society (ATS/ERS) recommendations.23 292.5) were made by extrapolation from detailed air quality monitoring in the homes of 179 children, participating schools and outdoor settings.2.5 concentrations were measured using PurpleAir PA-II-SD sensors .Estimates of each child’s personal 24-hour exposure to fine particulate matter  expressed as z-scores using Global Lung Initiative 2012 reference equations for African-American ethnicity in the absence of more appropriate Kenyan reference equations.As in many epidemiological studies of asthma prevalence in children, asthma prevalence estimates were based on the responses to the questions ‘Has child had wheezing or whistling in the chest in the past 12 months?’(current wheeze), ‘Has child ever had asthma?’ (ever asthma), and ‘Has child used any inhaled medicines, for example, puffers to help his/her breathing problems at any time in the past 12 months?’ .Unadjusted and adjusted analyses were conducted. Adjusted analysis included potentially confounding covariates identified by literature review as being associated with wheezing outcomes and birth parameters  which were available and measured and/or those environmental exposures significantly associated with outcomes in the primary analysis2.5 exposures.23Recruitment took place between January 2020 and November 2021 with a 14-month COVID-19 related suspension between March 2020 and April 2021. In total, 2373 schoolchildren were recruited; 1277 in Mukuru and 1096 in Buruburu. The characteristics of these children are presented in detail elsewhere and in 1 z-score. Of the children with birth weight and IWG data from the child immunisation booklets, spirometry was available for 209 and 329 children, respectively.1 and FVC z-scores. IWG was negatively associated with FEV1/FVC z-score with a p value of 0.053. Further analyses including preterm birth in the models with birth weight made little difference in the magnitude of the estimates of the ORs/regression coefficients. Inclusion of FEV1, FVC, FEV1/FVC as absolute values with age, height and sex in the models made little difference to the findings apart from the association between IWG and FEV1/FVC percentage that achieved statistical significance, β=−3.80 (95% CI −7.12 to –0.48), p=0.025. Classifying spirometry into obstructed  or restricted (FVC<LLN) indicated that 51 (3.1%) of children had obstructed and 39 (2.4%) had restricted spirometry and that birth weight was negatively associated with the odds of restricted spirometry OR 0.11 (95% CI 0.02 to 0.78), p=0.027.In adjusted multivariable logistic regression models, preterm birth was positively associated with the symptoms of ‘current wheeze’, ‘trouble breathing’, and ‘dry nocturnal cough’ . There w1 and FVC and reduced likelihood of restricted spirometry. We also highlight a negative association between IWG in the first year and FEV1/FVC ratio with a p value of 0.053. This is the first report of associations between preterm birth, birth weight and possibly IWG in relation to childhood symptoms consistent with asthma (current wheeze) and spirometry in a single sub-Saharan African setting and highlight the importance of early life factors in the aetiology of asthma and the life course of lung function in sub-Saharan Africa. These findings implicate the high rates of preterm birth, low birth weight and possibly poor IWG observed in sub-Saharan Africa as potentially important contributory factors to the prevalence of asthma, and obstructive and restrictive spirometry in sub-Saharan Africa.1–8 18 24 25In this observational cross-sectional study of children attending schools in two socioeconomically contrasting areas of Nairobi, Kenya, we report that preterm birth is associated with increased likelihood of the symptoms ‘current wheeze’, ‘trouble breathing’, ‘dry nocturnal cough’ and that birth weight is positively associated with FEV1; and children born preterm, with low birth weight and higher IWG are more likely to have lower FEV1/FVC ratio.1 or between preterm birth, birth weight and FEV1/FVC, our findings with relation to wheezing, FEV1 and FEV1/FVC ratio from a relatively small study in a sub-Saharan country are entirely compatible with meta-analyses of studies conducted in HICs that are several orders of magnitude greater in size.Studies in HICs with meta-analysis of very large numbers of children have reported: preterm birth, low birth weight and higher IWG are positively associated with wheezing and asthma; preterm birth, low birth weight and lower IWG are negatively associated with FEV1 reported in the current study. In South Africa, the Drakenstein child health study reported that birth weight z-score and gestational age at birth were associated with respiratory rate, functional residual capacity and respiratory system compliance measured in infants at 6–10 weeks of age.1 and FVC are intuitively consistent with the associations reported in Drakenstein.In sub-Saharan Africa, a few studies have related birth weight and preterm birth to early childhood respiratory outcomes, however, no single study in sub-Saharan Africa has investigated respiratory symptoms, spirometry, preterm birth, birth weight and IWG. In Mozambique, a case–control study of children aged 18 months to 8 years compared 100 children hospitalised with asthma to 99 age-matched controls, there was no association between low birth weight and asthma.1 and FVC in the absence of any effect on the rate of preterm birth.35 36Further studies are needed to investigate whether antenatal interventions to increase birth weight and reduce premature birth, for example, maternal nutrition, air pollution exposure, reduce the risk of childhood asthma and improve childhood lung function. The limited data to date suggest that preterm birth and birth weight are not on the causal pathway to lung disease but reflect exposure to factors that influence not only fetal growth but also, to a variable extent, lung development/disease. In Nepal, a multiple micronutrient supplement during pregnancy increased birth weight but had no effect on childhood lung function or asthma,The strengths of the current study include the number of schoolchildren recruited, the use of widely accepted methodologies to investigate childhood asthma, that spirometry was conducted to international standards and that we were able to adjust for the effects of several potential confounding environmental exposures that we have shown to be associated with respiratory outcomes in this setting.38The further limitation of the study is that we can only report associations because of the cross-sectional study design, and although we adjusted for potential confounding factors already identified we cannot exclude the possibility of residual confounding by unmeasured or mismeasured exposures, for example, parental asthma/allergic disease and maternal factors related to the study child’s pregnancy—nutrition, body mass index, age and parity. A further limitation is that we were particularly reliant on reports of respiratory symptoms instead of the metric ‘doctor diagnosed asthma’ that is a widely used and accepted measure of asthma prevalence in HICs. In sub-Saharan Africa ‘doctor diagnosed asthma’ is less reliable because asthma is underdiagnosed and undertreated,1, FVC and possibly IWG and FEV1/FVC. These findings are in keeping with those reported in HICs and highlight the importance of antenatal factors in the aetiology of asthma and lung function abnormalities in sub-Saharan Africa. Interventions that target the first 1000 days from conception have the potential for important benefits for lifelong respiratory health in sub-Saharan Africa.In the first study in sub-Saharan Africa to relate birth characteristics to both childhood respiratory symptoms and lung function, associations have been demonstrated between: preterm birth and respiratory symptoms; between birth weight and FEV