Environmental enteric dysfunction (EED) may contribute to adverse birth outcomes in low-resource settings. We examined the associations of EED biomarkers with birth outcomes in pregnant women living with human immunodeficiency virus in Dar es Salaam, Tanzania.We performed a cohort study of 706 HIV-infected pregnant women. Maternal serum samples collected at 32 weeks gestation were analyzed for markers of EED , systemic inflammation (C-reactive protein and α1-acid glycoprotein [AGP]), and growth hormone resistance  were assessed using linear and log-binomial regression models adjusted for multiple sociodemographic and clinical variables.trend=0·02). Higher AGP was associated with lower birthweight and was associated with increased risk of small-for-gestational age births. Higher IGF-1 was associated with higher birthweight and birthweight-for-gestational age while higher FGF21 was associated with shorter gestation and higher risk of preterm birth.Maternal EED biomarkers were not significantly associated with birthweight, gestation duration, or birthweight-for-gestational age. However, higher quintiles of I-FABP concentrations were associated with greater risk of stillbirth (pMaternal biomarkers of EED, systemic inflammation, and growth hormones were differentially associated with birth outcomes. Biomarkers of EED may be useful to identify pregnant women at risk of adverse birth outcomes, but further research is needed to confirm these findings and elucidate biological mechanisms.10.13039/100000002National Institutes of Health. Women living with HIV have a higher risk of adverse birth outcomes, although the reasons for this are not fully understood. Environmental enteric dysfunction (EED), a subclinical condition of the small intestine resulting in increased gut permeability, nutrient malabsorption, gut and systemic inflammation, and growth hormone resistance, may increase the risk of adverse birth outcomes. Very few studies have examined biomarkers of any of these domains among women living with HIV during pregnancy, particularly in sub-Saharan Africa where EED is widespread.In this prospective cohort study among 706 women living with HIV in Dar es Salaam, Tanzania, we examined the associations of maternal biomarkers of EED, systemic inflammation, and growth hormone resistance with birthweight, birthweight-for-gestational age, and gestation duration. In secondary analyses, we examined associations between these biomarkers with low birthweight, small-for-gestational age, preterm birth, and stillbirth. Although biomarkers of EED were not associated with our primary outcomes, increased maternal intestinal fatty acid-binding protein (I-FABP), a marker of gut epithelial barrier integrity, was associated with increased risk of stillbirth. Furthermore, increased AGP, a marker of systemic inflammation, was associated with lower birthweight and increased risk of small-for-gestational age births. Growth hormones related to growth promotion and regulation were also associated with birthweight and birthweight-for-gestational age, as well as gestation duration and preterm birth. This study examines these multiple domains of EED among women living with HIV and their associations with birth outcomes.Maternal biomarkers of EED, systemic inflammation, and the growth hormone axis were differentially associated with adverse birth outcomes, and the relationships were not consistent among biomarkers within these respective domains. Some of the biomarkers examined may be useful to identify pregnant women at risk of adverse birth outcomes and could play a role in the design and evaluation of interventions that address EED, inflammation, and promote healthy pregnancies to improve birth outcomes. Further studies are needed to confirm these results and elucidate the potentially different biological mechanisms involved.Alt-text: Unlabelled box,Adverse birth outcomes, such as stillbirth, low birth weight (LBW), small for their gestational age (SGA), and preterm birth remain major health concerns in low-income and middle-income countries (LMICs).,,The increased metabolic needs of pregnancy are accompanied by morphological changes to the gastrointestinal tract such as villus hypertrophy.,Limited studies have examined the relationship between EED biomarkers and birth outcomes among PWLHIV. Small case-control studies among PWLHIV in Spain and India have reported that increased lipopolysaccharide-binding protein (LBP), soluble CD14 (sCD14), soluble CD163 (sCD163), and intestinal-fatty acid binding protein (I-FABP) were associated with increased risk of preterm birth,,,,,,One of the features of EED is systemic inflammation,The possible roles of maternal EED, systemic inflammation, and growth hormone resistance on poor birth outcomes have not been well studied, especially among PWLHIV in LMIC settings. Therefore, we evaluated the association of biomarkers of EED, systemic inflammation, and the growth hormone axis at 32 weeks gestation with birth outcomes among PWLHIV in Dar es Salaam, Tanzania.3 supplementation for pregnant women living with HIV in urban Dar es Salaam, Tanzania. .,We conducted a prospective cohort study of participants who were enrolled in a randomized, parallel-group, triple-blind placebo-controlled trial of vitamin DUsing SAS , we randomly selected 725 participants, using a simple random sample of all 2300 participants enrolled in the trial. Participants were eligible for the EED study and assessment of the panel of biomarkers if they had a serum sample available at the 32-week gestation visit. Based on our calculation, a sample size of 600 is needed to have a 90% power to detect an effect size of 0·018 , with significance level  of 0·05, one tested predictor, and ten additional independent covariates. We increased our sample size to 725 to account for a possible 17% loss to follow-up. We additionally restricted analysis to singleton births.Escherichia coli LPS (1 µg/well) or Escherichia coli flagellin (100 ng/well). Serum samples were diluted (1:500) and then applied to wells coated with LPS or flagellin, followed by incubation and washing. Next, wells were incubated with anti-IgA  or anti-IgG  coupled to horseradish peroxidase. Total immunoglobulins were quantitated via colorimetric peroxidase substrate tetramethylbenzidine using an ELISA plate reader. Samples were read at 450nm and 540nm, and concentrations are reported as optical density (OD) units corrected for background value blanks. Serum samples were also processed at Quansys Biosciences , on the Q-Plex™ Human Environmental Enteric Dysfunction multiplexed ELISA array, also known as the Micronutrient and EED Assessment Tool (MEEDAT). MEEDAT measures two indicators of EED: I-FABP which is indicative of gut epithelial barrier integrity (damage/repair) as well as sCD14 which is indicative of monocyte activation and is a marker of microbial translocation through the intestinal epithelial barrier. MEEDAT additionally measures acute phase systemic inflammation , as well as hormones involved in the insulin-like growth hormone axis (insulin-like growth factor 1 [IGF-1] and fibroblast growth factor 21 [FGF21]). Per the manufacturer's recommendation, a serum dilution of 1:10 was used. Quantitative concentrations were calculated, and the lot lower limit of quantification (LLOQ) and the lot upper limit of quantification (ULOQ) were calculated using calibrator curves. All values below the lot lower limit of detection (LLOD) were substituted with a value of half the value of the LLOQ, and all values between the LLOD and LLOQ were extrapolated using calibrator curves, as were values above the ULOQ. All values that were incalculably high  were included in quartile analyses but excluded from secondary log2 analyses. The intra-assay precision for anti-flagellin IgA and IgG and anti-LPS IgA and IgG was 9.2%, 11.4%, 9.8%, and 12.5% respectively. The intra-assay precision for sCD14 was 4%, I-FABP was 6%, for CRP was 3%, for AGP was 5%, IGF-1 was 7%, and for FGF21 was 4%. Detailed laboratory methods used for the MEEDAT panel are found in Appendix 1, and information about its validation has been previously published.All samples selected for the cohort study were to have the full panel of EED, systemic inflammation and growth hormone biomarkers quantified. ELISA methods were used to measure anti-flagellin and anti-LPS Ig concentrations (IgA and IgG) according to previously reported methods.st standards.th percentile birthweight for gestational age by sex according to INTERGROWTH-21st standards.The primary outcomes of the study were birthweight in grams, gestational duration in weeks, and birthweight for gestational age z-scores. Study nurses and midwives attending the labour and delivery assessed birthweight among participants giving birth in Dar es Salaam. Birthweights for deliveries at study facilities were measured to the nearest 5 g using a digital scale . Information on deliveries outside of Dar es Salaam was obtained from medical records and attending clinical staff (∼10% of deliveries). LMP dating was used to determine gestation duration. Birthweight for gestational age z-scores were determined according to INTERGROWTH-212 transformations. In these models, each unit increase in log2 concentration is interpreted as a doubling of the biomarker concentration.Biomarkers were categorized into quartiles, with the lowest quartile as the reference group. Linear regression models with robust standard errors to address deviations from normality were used to assess the relationship between biomarker quartiles and continuous outcomes. Log-binomial regression models were used to assess the relative risk of binomial outcomes by biomarker quartiles.2, 18·5-24·9 kg/m2, 25·0-29·9 kg/m2, ≥30 kg/m2), marital status , education , socioeconomic status (SES), clinic site, World Health Organization (WHO) HIV disease stage , CD4 T-cell count , the timing of ART initiation (before vs during pregnancy), infant sex , and randomized regimen (vitamin D3 vs. placebo). SES was defined according to household ownership of assets , and was categorized into quintiles using a principal components analysis. We also conducted sensitivity analysis that adjusted for CRP to address the potential contribution of systemic inflammation. The missing indicator method was used to retain individuals with missing covariates when a missing covariate applied to more than 1% of participants, which applied to maternal BMI (1.1% missing) and CD4 count (47.0% missing). In order to assess the robustness of the missing indicator method, we conducted sensitivity analyses using multiple imputation with chained equations to impute missing covariate data for maternal BMI (1.1% missing) and CD4 T-cell count (47.0% missing). Early during the conduct of the trial, the HIV care and treatment program discontinued routine CD4 T-cell assessment after ART initiation, and switched to only HIV-1 viral load assessments every 6 months of ART treatment. The trial relied on the program for CD4 counts and therefore after programmatic discontinuation, CD4 counts are missing for the later trial enrollments. Thus, CD4 counts were not available for all participants. All analyses were conducted in STATA 15 .Multivariable models included adjustment for maternal age , body mass index (BMI) , the Tanzanian National Health Research Ethics Sub-Committee , the Muhimbili University of Health and Allied Science Institutional Review Board (2016-05-25/AEC/Vol.X/01) and the Tanzania Food and Drug Authority . All participants provided written informed consent for collection of blood and storage of samples for future studies in the parent trial. This ancillary study was approved by Boston Children's Hospital =0·02; p-value derived from log binomial model). Women in the highest quartile of I-FABP at 32 weeks gestation had more than twice the risk of stillbirth compared to those in the lowest quartile   (Table S10). There was also a trend between quartiles of LPS IgA and stillbirth, but the results were not statistically significant . In continuous analysis, each unit increase in log2 transformed LPS IgA was associated with an increased risk of stillbirth  (Table S10). The findings for the relationship of I-FABP and LPS IgA with stillbirth were consistent when additionally adjusting for CRP .In secondary analyses, we found that increased maternal I-FABP quartiles were significantly associated with increased risk of stillbirth (p for trend [p00-5·97) . Corresptrend=0·01; p-value derived from linear regression model) in multivariate analyses. Infants whose mothers were in the highest quartile of AGP weighed 163 g less (95% CI -269 to -57g) on average than infants whose mothers were in the lowest quartile , with those in the highest quartile having a 69% increase in the risk of SGA compared to the lowest quartile  . In analyses of continuous AGP, each unit increase in log2-transformed AGP was associated with reduced birthweight  (Table S9). Quartiles and log2-transformed (continuous) CRP were not associated with any birth outcome.Increases in maternal AGP quartiles were significantly associated with lower infant birthweight (pquartile . Similar07-2·65) . Increastrend =0·003; p-value derived from linear regression model), with mothers in the highest quartile giving birth to infants that weighed 172g more than those in the lowest quartile (95% CI 64 to 281g) ; infants born to mothers in the highest quartile had a 0·4 SD higher z-score compared to those in the lowest quartile of IGF-1 (95% CI 0·1 to 0·7 SD). IGF-1 was not associated with stillbirth, gestation duration, or the risk of preterm birth. These relationships were consistent after adjustment for CRP .Increases in maternal IGF-1 were significantly associated with higher birthweight (pto 281g) . Quartiltrend =0·03; p-value derived from linear regression model); those in the highest quartile had a gestational duration 0·6 weeks shorter (95% CI -1·1 to -0·1 weeks) than those in the lowest quartile  (Table S9). Increased FGF21 concentrations were also significantly associated with the risk of preterm birth ; women with FGF21 in the highest quartile had a 77% higher risk of delivering a preterm birth as compared to the lowest quartile . In continuous analyses, each unit increase in log2 transformed FGF21 was associated with 26 gram lower birthweight , an 11% increase in the risk of SGA , and a 12% increase in the risk of preterm birth . Adjustment for CRP did not meaningfully change these estimates (S11 and S12).Increases in quartiles of FGF21 were associated with shorter gestation . Similarly, in sensitivity analyses of binary outcomes, the results for the relationship between I-FABP and stillbirth, AGP and SGA, and FGF21 and preterm birth, were qualitatively similar when using multiple imputation to account for missing maternal BMI and CD4 T-cell count covariate data (S17-S19).In this prospective cohort study of PWLHIV in Tanzania, we found no association of maternal EED biomarkers related to microbial translocation  or gut epithelial damage (I-FABP) with our primary outcomes of birthweight, gestation duration, or birthweight for gestational age. However, increased quartiles of maternal I-FABP and greater anti-LPS IgA concentrations, biomarkers of EED , were associated with increased risk of stillbirth, a secondary outcome. We also found that increased AGP, a marker of chronic systemic inflammation, was associated with reduced birthweight and increased risk for SGA births. Higher IGF-1 was associated with increased birthweight and birthweight-for-age z-score, while higher FGF21 was associated with shorter gestation duration and was associated with increased risk of preterm birth.Our finding of no significant association of any maternal EED biomarker in pregnancy with birthweight or gestation duration is in contrast to our earlier study in Uganda among HIV-negative women that found that higher levels of anti-flagellin IgG and anti-LPS IgG were associated with shorter gestational length, as well as decreases in birth length.Our finding of an association between the EED biomarkers of I-FABP and LPS IgA with stillbirth is intriguing. Further, these associations were also observed when controlling for CRP, which suggests that intestinal wall integrity and microbial translocation may contribute to stillbirth independent of systemic inflammation in the study population, although systemic inflammation may also be a mediator between EED and birth outcomes. The root causes of stillbirth can be multifactorial and are often unreported or challenging to determine, but may stem in part from poor nutrition, abnormal angiogenesis, foetal asphyxia/hypoxia, infections, local and systemic inflammatory responses, pre-eclampsia, antepartum haemorrhage, or placental conditions.,,,We also found that increased AGP concentrations, an indicator of chronic systemic inflammation, were associated with lower birthweight and increased risk of SGA. However, there was no association of CRP, an indicator of acute systemic inflammation, with any birth outcome. Inflammation during pregnancy has been previously linked to adverse pregnancy outcomes.,Higher maternal IGF-1, a key hormone in the growth hormone-IGF axis, was associated with increased birthweight and birthweight-for-age z-score. This was unsurprising, as IGF-1 is an important promoter of growth and plays a role in placental function and foetal development.Although our study has a number of strengths, including a >99% follow-up rate and examination of multiple domains of EED, systemic inflammation, and the growth hormone axis, there are several limitations. First, given the observational design of the study, we cannot infer causality from these associations, as there may be unmeasured  or residual confounding. Second, LMP dating was used and therefore it is likely that there is some misclassification in gestation duration and preterm birth outcomes; however, it is likely that misreport of LMP is non-differential with respect to the biomarkers evaluated which would therefore attenuate measures of association. Similarly, there may be some degree of measurement error in birthweight, particularly for deliveries outside of study clinics. Future studies could be strengthened through more accurate dating approaches such as early pregnancy ultrasound. We also collected blood samples at 32 weeks gestation and therefore were not able to evaluate the relationship of EED biomarkers earlier in pregnancy with birth outcomes nor the relationship of EED with very preterm birth, miscarriage or other events that occur before 32 weeks gestation. Future studies could also examine these biomarkers at multiple time points during pregnancy (including first and second trimester), and evaluate potential associations with miscarriage and foetal loss earlier in gestation. In addition, we cannot determine whether these biomarkers of EED, inflammation and the growth hormone axis preceded or resulted from adverse events  during gestation. Repeated sampling throughout pregnancy could be informative, along with an examination of a wider array of inflammatory and metabolic markers, as well as the use of intestinal biopsies to confirm the presence and severity of EED. Furthermore, we did not correct for multiple hypothesis testing and cannot rule out the possibility that our findings of associations were due to Type 1 errors (incorrectly rejecting the null hypothesis) due in part to multiple testing. Lastly, this study was among PWLHIV in urban Tanzania, with observed low levels of maternal undernutrition which is characteristic of some urban settings in East Africa. Therefore, while the sample is representative of PWLHIV attending HIV clinics in Dar es Salaam, the findings may not be generalizable to other populations and settings.In conclusion, maternal biomarkers of EED, systemic inflammation, and the growth hormone axis were differentially associated with adverse birth outcomes, and the relationships were not consistent among biomarkers within these respective domains. Although we hypothesized that biomarkers of EED would be associated with adverse birth outcomes among PWLHIV, we did not find significant associations with birthweight, gestation duration, or birthweight-for-gestational age. However, higher I-FABP, a marker of gut epithelial damage, was associated with increased risk of stillbirth. Furthermore, increased systemic inflammation as measured by AGP was associated with decreased birthweight and was associated with increased risk of small-for-gestational age birth. Lastly, hormones related to growth promotion and regulation were associated with adverse outcomes – higher IGF-1 was associated with increased birthweight and birthweight-for-gestational age, while higher FGF21 was associated with shorter gestation duration and increased risk of preterm birth. Further studies are needed to confirm these results and elucidate the potentially different biological mechanisms involved. Taken together, some of the biomarkers examined may be useful to identify pregnant women at risk of adverse birth outcomes and could play a role in the design and evaluation of interventions that address EED, inflammation, and promote healthy pregnancies to improve birth outcomes.Conceptualization: Miles A. Kirby, Jacqueline M. Lauer, Wafaie W. Fawzi, Karim P. Manji, Christopher P. Duggan, Christopher R. Sudfeld.Data curation: Miles A. Kirby, Jacqueline M. Lauer, Christopher R. Sudfeld.Verification of the underlying data: Miles A. Kirby, Christopher R. Sudfeld.Formal analysis: Miles A. Kirby, Christopher R. Sudfeld.Funding acquisition: Jacqueline M. Lauer, Robert K.M. Choy, Michael B. Arndt, Andrew Gewirtz, Christopher R. Sudfeld, Karim P. Manji, Said Aboud, Wafaie W. Fawzi, Christopher P. Duggan.Investigation: Christopher R. Sudfeld, Jianqun Kou, Andrew Gewirtz, Karim P. Manji, Alfa Muhihi, Said Aboud, Wafaie W. Fawzi, Christopher P. Duggan.Methodology: Christopher R. Sudfeld, Robert K.M. Choy, Michael B. Arndt, Jianqun Kou, Andrew Gewirtz, Alfa Muhihi, Said Aboud, Nzovu Ulenga, Wafaie W. Fawzi, Karim P. Manji, Christopher P. Duggan.Project administration: Miles A. Kirby, Christopher R. Sudfeld, Karim P. Manji, Alfa Muhihi, Said Aboud, Wafaie W. Fawzi, Christopher P. Duggan.Supervision: Christopher R. Sudfeld, Robert K.M. Choy, Karim P. Manji, Alfa Muhihi, Said Aboud, Nzovu Ulenga, Wafaie W. Fawzi, Christopher P. Duggan.Writing – original draft: Miles A. Kirby, Christopher R. Sudfeld, Christopher P. Duggan.Writing – review & editing: Miles A. Kirby, Jacqueline M. Lauer, Alfa Muhihi, Nzovu Ulenga, Said Aboud, Enju Liu, Robert K.M. Choy, Michael B. Arndt, Jianqun Kou, Andrew Gewirtz, Wafaie Fawzi, Christopher P. Duggan, Karim P. Manji, Christopher R. Sudfeld.Decision to submit for publication: Christopher P. Duggan, Karim P. Manji, Christopher R. Sudfeld.All authors read and approved the final version of the manuscript.ghp@hsph.harvard.edu and completion of ethical approval and data transfer agreement from the Tanzania National Institute of Medical Research (http://reims.nimr.or.tz:8010/guides/DTA.pdf).The full dataset cannot be shared publicly because of our study's requirement for ethical approval and data transfer agreement. The deidentified dataset supporting this research may be made available following a submitted request to Christopher Duggan declares royalty payments from UpToDate, Inc. The other authors have declared that no competing interests exist.


In vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) is associated with an increased risk of preterm  and early preterm birth . The underlying general and procedure related risk factors are not well understood so far. 4328 infertile women undergoing IVF/ICSI were entered into this study. The study population was divided into three groups: (a) early preterm birth group (n = 66), (b) preterm birth group (n = 675) and (c) full-term birth group (n = 3653). Odds for preterm birth were calculated by stepwise multivariate logistic regression analysis. We identified seven independent risk factors for preterm birth and four independent risk factors for early preterm birth. Older (> 39) or younger (< 25) maternal age , multiple pregnancy , placenta previa , and embryo reduction  were associated with preterm birth and early preterm birth, whereas gestational hypertension , elevated triglycerides  and shorter activated partial thromboplastin time  were associated only with preterm birth. In conclusion, preterm and early preterm birth risk factors in patients undergoing assisted IVF/ICSI are in general similar to those in natural pregnancy. The lack of some associations in the early preterm group was most likely due to the lower number of early preterm birth cases. Only embryo reduction represents an IVF/ICSI specific risk factor. Furthermore, those infants who do survive have higher rates of long-term morbidities, including cardiovascular diseases2 as well as neurologic and developmental disabilities, compared to infants born full term. Known maternal risk factors for preterm birth in the general population include having a previous premature birth, twin pregnancy, an interval of less than six months between pregnancies, history of multiple miscarriages or abortions, smoking cigarettes or using illicit drugs, cardio-metabolic diseases such as hypertension or diabetes, and infections, particularly of the amniotic fluid and lower genital tract7. Conceiving through in vitro fertilization represents another risk factor in a subgroup of women undergoing assisted reproduction technologies (ART). The risk factors increasing the likelihood for preterm birth in this particular population are, however, as of today, not well understood. Numerous studies8 analyzed maternal and offspring outcomes after ART, whereas larger sized studies focusing specifically on the risk factors for preterm birth and especially early preterm birth especially associated to poor offspring outcome are lacking. However, this is a clinically important topic, since the understanding of ART related risk factors for preterm birth might identify changeable factors offering potential treatment options to improve offspring short term and long-term outcome in women undergoing ART. The aim of the current study was to identify causes or medical reasons for preterm and early preterm birth in a large cohort of women who underwent ART.There are more than 15 million preterm infants every year among the world, accounting for 10% of the total newborn infants, of which the incidence of preterm delivery in China ranks the second. Preterm delivery accounts for more than 75% of perinatal morbidity and mortality worldwideThe study was approved by the ethics committee of Reproductive & Genetic Hospital of Citic-Xiangya, Changsha, China . A total of 4349 infertile women who had undergone IVF/ICSI treatment and obtained live birth in the Reproductive & Genetic Hospital of Citic-Xiangya from January 1st, 2016 to December 30th, 2017 were enrolled.9Women treated with super-ovulation protocols exactly as described previously Fresh embryo transfer recipients, who received IVF/ICSI treatmentGiving live birth after ARTInclusion criteria were as follows:Using donor sperms or donor eggs for ARTComplete clinical data were not availablePost-term birth (> 42nd week of gestation) cases were excludedInfertile couples with known female or male genetic causes of infertilityExclusion criteria were as follows:10. Note: Gestational age was determined as the 17th day of gestation when a 6–8 cell embryo was transferred into the uterus and as the 19th day of gestation when a blastocyst was transferred.Gestational age was calculated by adding 2 weeks (14 days) to the number of days since fertilization11. Early preterm birth was defined as a live birth with a gestational age between 20 but not over 32 weeks 12.Full-term birth was defined as a live birth with a gestational age between 37 but not over 42 weeks . Preterm birth was defined as a live birth with a gestational age of at least 20 but not over 37 weeks All patient’s data  used in our study were extracted from the routine electronic patient records used in our hospital.Informed consent was obtained from all subjects and/or their legal guardian(s). A structured medical history was taken. The following risk factors for preterm birth were examined in this study:Maternal risk factors: (1) basic parameters before super-ovulation: nationality, education, age, body height, body weight, infertility duration, types of infertility, causes of infertility , blood pressure readings. (2) Pregnancy history: parity, artificial abortion, drug abortion, spontaneous abortion, ectopic pregnancy, number of deliveries, vaginal delivery, cesarean section (3) blood test result before super-ovulation: liver and kidney function, lipid items, blood coagulation function. (4) Pregnancy related factors: multiple pregnancy, embryo reduction, gestational diabetes, gestational hypertension, placenta previa.Relevant risk factors during IVF/ICSI procedure: cycle count, fertilization way, embryo transfer type (blastocyst or cleavage stage embryo transfer), ovulation induction scheme, source of sperm, transferred embryo count, dosage of gonadotropin, ovulation inducing days.Offspring data: gestational age at delivery, gender, birth weight.Basic parameters about the mother, pregnancy history, gynecological complications, and relevant risk factors during IVF/ICSI procedure came from the case report in the hospital. Furthermore, blood test results from maternal blood taken before the beginning of superovulation was extracted from the case report. Pregnancy related factors and offspring data were followed up strictly by a special nurse.This study is a retrospective study. Data were obtained through the electronical medical record system of the hospital. Patients were not directly involved in this study. The patients were unaware of the results of the study.1 − Q3) for non-normally distributed variables and Mann–Whitney nonparametric test was used for comparison of variables between groups. Categorical variables are described as frequency and percentages. Pearson’s chi-square test was used for testing qualitative data and Fisher's exact test was used when the expected frequencies were < 5%.Continuous variables are represented as mean ± SD for normally distributed variables and student’s unpaired t-test was used for comparison of variables between two groups. Continuous variables are represented as median and quartiles M  was used to perform all data analyses and a two-sided All methods were carried out in accordance with relevant guidelines and regulations of the People Republic of China.This study was approved by the ethics committee of the Reproductive and Genetic Hospital of CITIC-Xiangya, Changsha, China . The data of this study is only used for this study, and the data of patients are strictly confidential. This study will not cause any harm to the patients' body and mind.2. The study cohort consisted mostly of Han Chinese women (87.8%). Caused for infertility in the entire study populations were distributed as follows: primary infertility was present in 42.9% and secondary infertility in 57.1%. The duration of infertility was 4  years. Median birthweight was 3100  g, Median gestational age was 38.4  weeks. For more details see Tables From the primary dataset of 4349 treated women, we excluded 13 cases in which the gestational age was unclear and 8 cases that were post-term pregnancies. Thus finally 4328 cases were included into the study, 3653 of them were full-term deliveries. The prevalence of preterm birth and early preterm birth was 15.5% and 1.8% respectively , including 6 maternal parameters , 5 pregnancy related factors , 2 factors related to the IVF/ICSI procedure (embryo transfer type and number of embryos transferred) and 2 offspring related factor (infant sex and intrauterine growth retardation) , including 3 maternal parameters , 3 pregnancy related factors , 3 factors related to the IVF/ICSI procedure , 1 offspring related factor (infant sex)  remained significant in the multivariate analysis model for early preterm birth  were left in the multivariate analysis model for preterm birth. With regard to early preterm birth, the above described 10 factors, see above, were entered into the multivariate analysis. After stepwise regression analysis, 4 factors P = 0.009) and early preterm birth ratio by 1.13 times . Compared to singleton pregnancies, mothers with multiple pregnancies had a significantly increased preterm birth ratio by 8.78 times  and early preterm birth ratio by 7.58 times . Embryo reduction significantly increased preterm birth ratio by 2.54 times  and early preterm birth ratio by 6.14 times . Placenta previa increased also significantly both preterm birth ratio by 13.95 times  and early preterm birth ratio by 15.48 times . The presence of gestational hypertension, higher triglycerides and a shorter activated partial thromboplastin was significantly associated with preterm birth  but not early preterm birth (P > 0.05)  and also older mothers (> 40 years old) displayed a significantly increased preterm birth ratio by 0.50 times  or younger (< 25) maternal age, multiple pregnancy, placenta previa, and embryo reduction surgery were associated with an increased risk for both preterm birth and early preterm birth after IVF/ICSI. Gestational hypertension, higher triglycerides and a shorter activated partial thromboplastin time were only associated with an increased occurrence of preterm birth but not early preterm birth. However, the lack of some associations in the early preterm group was most likely due to the lower sample size.13. A recent meta-analysis of cohort studies demonstrated that the incidence of preterm birth in IVF/ICSI group and naturally conceived controls are 4.73% and 1.81%, respectively14. The underlying risk factors for preterm birth in this population, however, are not fully established so far. The current study, investigating a cohort of women who underwent ART, identified several factors which were associated with preterm birth. The majority of the identified factors, such as maternal age15, multiple pregnancies, placenta previa, gestational hypertension, high triglycerides and hypercoagulability17, have previously been shown to be associated with an increased risk for preterm birth in the general population as well.The variable “preterm birth” used in this study includes spontaneous and iatrogenic preterm birth. In several studies, it was already shown that the risk of preterm birth among singleton IVF/ICSI pregnancies was significantly higher than that occurring in spontaneous conceptions 18. However, there is also a study with a similar study design as our study showing that women aged 25–29 were at an increased risk for preterm birth in comparison to women aged 30–34. Women aged ≥ 35 years did not display an increased risk of any type of preterm birth19. These previous findings may suggest that while there is a positive association between maternal age and the risk for preterm birth, younger women who conceived via ART may display a higher risk for preterm birth compared to older women who conceived undergoing ART. As the proportion of women who conceive with ART also shows an age-related increase, these results may also reflect the increased clinical risk of adverse birth outcomes among young women who needed ART to conceive18.Our study showed an increased risk for preterm delivery in association with maternal age. Both younger and older women after ART treatment had an increased risk for preterm birth in our study as it was likewise seen in studies addressing this topic in the general population. Somewhat smaller study done in an ART population mainly reported similar associations 21. The underlying reasons for a higher frequency of gestational hypertension in ART pregnancies remain incompletely understood. Wang et al. showed in a large cohort comparing ART pregnancies to natural conception that ART is associated with a higher prevalence for gestational hypertension, yet this association disappeared once data was stratified by multiple birth cases22. The authors concluded that multiple pregnancy which is associated with ART is the single most likely explanation for the increased rate of gestational hypertension among ART mothers.The current study also identified gestational hypertension as risk factor for preterm birth in women who needed ART to conceive. This finding is in line with the current literature, gestational hypertension was shown to be associated with an increased risk for preterm birth in both the general population and women who underwent ART. Moreover, it was shown that ART is associated with a higher frequency of gestational hypertension and preeclampsia as compared to natural pregnancy 23. A study that investigated mothers who had conceived both naturally and via ART, showed that the risk of placenta previa was three‐fold higher in the ART pregnancy24. The mechanisms underlying this phenomenon still have to be elucidated. It is hypothesized that ART related procedures, such as an induction of uterine contractions due to transcervical catheter insertion or the unique endocrinological environment with high estradiol concentrations following ART cycles might be responsible25.Another risk factor for preterm birth found by the current study is placenta previa. Placenta previa is associated with preterm birth in the general population as well 27. Pregnancy is a hypercoagulable state with an increased thrombotic risk throughout gestation and the postpartum period. Women with thrombophilia may have a further increased risk of placental vascular complications, including pregnancy loss, preeclampsia, intrauterine growth restriction, and placental abruption. Accumulating data suggest that maternal antithrombotic prophylaxis may result in improved gestational outcome28. Results from one small prospective study analyzing the relationship between maternal hypercoagulability and preterm labor in 76 women demonstrated a statistically significant procoagulant activity, expressed by a shorter prothrombin time and activated partial thromboplastin time, in pregnant women with premature uterine contractions who gave birth prematurely27. The presence of hypercoagulation before starting an IVF treatment was shown to be associated with negative IVF outcomes such as pregnancy loss. However, the mechanism of hypercoagulability associated with preterm birth is not extensively explored. Our study clearly established hypercoagulability as a risk factor for preterm birth in ART and hence may help to clarify ongoing debates on this subject29.Regarding maternal laboratory parameters recorded before super-ovulation, the current study demonstrated a positive association between maternal triglycerides, shorter activated partial thromboplastin time and preterm birth. Both high triglycerides and hypercoagulability were already shown to be associated with an increased risk for preterm birth in the general population26. In a retrospective cohort of 2.9 million pregnant women in California, maternal diagnosis of dyslipidemia was significantly associated with increased risk for preterm birth30. Also, some studies investigated lipid levels and ART outcomes and showed that maternal triglyceride was inversely associated with live birth rate. However, data regarding the relationship between maternal triglycerides and preterm birth in the setting of ART are scarce31. Our findings may motivate further study regarding potential benefits of the treatment of hypercoagulability and hyperlipidemia in pregnancy and its effects on maternal–fetal outcomes.Regarding triglycerides, pregnancy is typified by an increase in serum levels of total cholesterol and triglycerides pushed by the rise in estrogen, progesterone and placental lactogen. Existing evidence has demonstrated that high maternal triglycerides levels during pregnancy are related to an increased risk for preterm birth in both obese women and in women with normal BMI in the general population conceiving naturally 32. Multiple pregnancy is considered one of the largest hazards of ART. Until now, ART is associated with a high number of multiple pregnancies due to the current policy transferring multiple embryos simultaneously to achieve a high pregnancy rate33. To reduce the risks associated with multiple pregnancy, embryo reduction is performed frequently. Previous meta-analyses have shown that embryo reduction improves outcomes in triplet pregnancies, but never to that degree of singleton pregnancies. An effective method to reduce the risk of multiple births in ART is an elective single embryo transfer, a policy that is adopted by an increasing number of guidelines. However, studies also demonstrated that elective single embryo transfer is not associated with a reduction in the risk for preterm delivery34.Our study is in good agreement with previous studies indicating that multiple pregnancy is a strong risk factor for preterm birth, both in the general population as well as in women who conceived trough ARTOur study has limitations. Firstly, the data of maternal pregestational diabetes, chronic hypertension and PE are missing in the electronic database. We mainly focused on causes or medical reasons for preterm birth. Secondly, only fresh embryo transfer recipients who received IVF/ICSI treatment were included in the current study. It is likely that fresh and frozen embryo transfer present different risks of PTB. We will therefore carry out frozen embryo transfers analyses in the future “”.35.In conclusion, our study demonstrated that maternal age, multiple pregnancy, embryo reduction and placenta previa could increase the risk of preterm birth in women undergoing IVF/ICSI. During ART treatment, the numbers of embryo transfers per cycle should be reduced to two or even to one thus reducing the need for embryo reduction procedures or multiple pregnancy. Strengthening antenatal care is necessary during pregnancy, especially for the patients with placenta previa. The finding that coagulation abnormalities are linked to preterm birth needs independent confirmation and if confirmed may stimulate clinical trials testing drugs interfering with the coagulation system as it is for example done in pregnant women suffering from activated protein C resistanceSupplementary Information.


Preterm birth, low birth weight and perinatal deaths are common adverse perinatal outcomes that are linked with each other, and a public health problems contributing to neonatal mortality, especially in developing countries. Although more than half of women in Ethiopia become pregnant within a short interval after the preceding childbirth, whether the short intervals increase the risk of adverse perinatal outcomes or not is understudied. We, therefore, aimed to assess the effects of inter-pregnancy intervals (IPIs) on the adverse perinatal outcomes.A community-based prospective cohort study was conducted among 2578 pregnant women in urban South Ethiopia. Pregnant women with IPIs < 24 months (IPIs < 18 and 18–23 months) were exposed groups, and those with IPI 24–60 months were the unexposed group. A multilevel analysis (mixed-effects) was done to estimate the effect of IPIs on preterm birth and low birth weight, and a generalized linear model for a binary outcome (fixed-effect) was done for perinatal deaths, using a 95% confidence level.In this study, IPI < 18 months found to increase the risk of preterm birth (Adjusted Relative Risk (ARR) = 1.35, 95% CI: 1.02, 1.78), term low birth weight  and perinatal deaths  than 24–60 months. The results suggest that, about 9% of preterm birth, 21% of term low birth weight and 41% of perinatal deaths in the study population were attributed to IPI < 18 months. These could be prevented with the removal of the IPI < 18 months in the study population. IPI 18–23 months has shown no effect on the three adverse perinatal outcomes.This study has shown that, IPI under 18 months has a higher risk of adverse perinatal outcomes than IPI 24–60 months. Due attention should still be given for spacing pregnancies.The online version contains supplementary material available at 10.1186/s40748-022-00138-w. We defined inter-pregnancy interval (IPI) as a time elapsed from live birth to a women’s last menstrual period (LMP) or conception . DuratioPreterm birth, low birth weight and perinatal deaths  are common adverse perinatal outcomes that are linked with each other, and a major public health concerns, especially in low and middle-income countries –10. GlobSeveral risk factors for preterm birth, low birth weight and perinatal deaths have been identified. To mention some: maternal education below secondary schooling, maternal age, parity, multiple gestation, pregnancy-induced hypertension, antepartum hemorrhage and premature rupture of membranes were associated with preterm birth –15. MateAmong those factors, we interested in IPI because there are feasible interventions globally to modify IPIs like modern contraceptive methods. In Ethiopia, in particular, there are health facility and community-based platforms/strategies for implementations such as health extension programs . There iTherefore, we aimed to assess the effect of short IPIs on the three adverse perinatal outcomes in urban south Ethiopia. The findings will add to the existing pieces of evidences to support recommendations and to have an in-depth understanding about to what extent preventing pregnancies that occur shortly after the preceding live births contribute to preventing the public health impacts of those adverse perinatal outcomes.A community-based prospective cohort study design was carried out among pregnant women in five urban settings  in the Hadiya zone, South Ethiopia. In this study, a total of 18 kebeles (lowest administrative unit in Ethiopia) were included.st trimester of confirmed pregnancy (after 12 weeks of gestation) via house-to-house identification and registration every three months, for a total of nine months. An enrolment was done from July 08, 2019 to March 30, 2020 by trained midwives. During the recruitment, study participants were included in the study based on the eligibility criteria for the exposure variable (IPI). The inclusion criteria were women who: were pregnant at the time of recruitment, had a live birth during the most recent childbirth, and were able to recall the date of last childbirth. Women who had a prior live birth ≥ 60 months earlier, a recent stillbirth, a recent abortion, and those who did not show a willingness to be followed were excluded.For this study, cohorts of pregnant women were enrolled at the end of 1A sample size of 2424 (exposed = 1212 and non-exposed = 1212) was calculated in Epi Info StatCalc version 7.2.2.6 software using the formula for Cohort study design, assuming % of unexposed  with outcome (low birth weight) = 8.52%, % of exposed  with outcome (low birth weight) = 11.97%, RR of 1.41, ratio of unexposed to exposed 1:1, 1-alpha of 1.96 (two sided) and 1-beta of 0.842 from previous study in Tanzania [The dependent/outcome variables were preterm birth, term low birth weight and perinatal deaths.Preterm birth is defined as a baby born alive before 37 completed weeks (28–36 weeks) of gestation.Term low birth weight is a live born baby’s weight at term birth  less than 2500 gms.Perinatal deaths are fetal death after 28 weeks of gestation up to 7 days, which include both stillbirth and early neonatal death.The exposure variable was inter-pregnancy interval  .Confounding variables were socio-demographic, and economic and reproductive variables such as maternal age, maternal education, husband education, maternal occupation, wealth status, mode of previous delivery, age at first childbirth, parity and pregnancy intention.Before baseline data collection, the questionnaire was prepared from existing related literature  based on the study objectives , 3, 24. Preterm birth was ascertained as a baby born alive before 37 completed weeks (36 weeks plus 6 days) but after 28 weeks of gestation. Gestational age was computed by subtracting the date of delivery from the date of childbirth and expressed in weeks. Then, gestational age was categorized as < 37 weeks (1 = preterm birth), and as ≥ 37 weeks (0 = otherwise).Term low birth weight was ascertained as a weight of a baby who born alive at term (≥ 37 weeks of pregnancy) with a birth weight of < 2500 g. The weight categorized as < 2500 g (1 = low birth weight) and as ≥ 2500 g (0 = otherwise).Perinatal deaths were ascertained as the death of the baby after 28 weeks of gestation and within 7 days postpartum (28 weeks up to 7 days). It includes both stillbirth  and early neonatal death (death of a live birth baby within 7 days after delivery). If at least one of them, either stillbirth or early neonatal death, happens then it was categorized as perinatal deaths .The exposure variable (IPI) was ascertained by asking women about the date of most recent childbirth and the last menstrual period. IPI was computed by subtracting the date of recent childbirth from the date of the last menstrual period (LMP). For women who had difficulty in recalling the date of LMP, Ultrasound was used to estimate gestational age. LMP was computed by subtracting the duration of gestation, and then the value of IPI was calculated . To be ist – 8th grade), secondary education (9th -12th grade) and higher education . The occupation was measured by asking the women the main occupation that they routinely do. Parity was measured as the number of times a woman gives birth, irrespective of the outcomes of birth (live birth or stillbirth). Age at first childbirth was measured as reported age at the time that a woman had her first child. Mode of previous delivery refers to whether a woman has given the most recent childbirth spontaneous vaginal delivery or by other routes  of delivery. Pregnancy intention was measured as whether a woman has the intention to be pregnant or not at the time of conception. Wealth index was measured using household assets for urban residence, which consists of the following items: owner of the house, number of rooms, the material of the roof, material of the floor, material of the exterior wall, source of drinking water, type of latrine, type of cooking materials , source of income, and presence or absence of; cell phone, refrigerator, radio, television, stove, chair, table, watch, modern bed, bicycle, bajaj (three wheel vehicle), motorcycle, car, donkey/horse cart, and bank account. Each item was categorized into two (1 = yes and 0 = no). Latrine and water sources were categorized as an improved and unimproved facility based on the world food program and World Health Organization recommendations. Principal component analysis was done to generate the components. Finally, the ranking was done into three quintiles .Potential confounding variables are those variables that have an association with an exposure (IPI) variable and the outcomes . These confounders were identified by prior theoretical knowledge and literature –18, 25. Data were entered in Epi-data version 3.1 software and exported to R version 4.0.5 software for the analysis. Before the analysis data cleaning and recoding were done for all variables. Categorization and recoding for continuous variables were done using information from related literature. Frequencies and percentages, using cross-tabulation, were calculated for categorical variables and discreet continuous variables. For missing data, a complete case analysis approach was applied.A generalized linear model for binary outcomes was used to assess the association of IPI with perinatal deaths. In the multivariable model, IPI was adjusted for all possible confounding variables, and a significant association with perinatal deaths was declared using a 95% confidence level and p < 0.05. For the other perinatal outcomes (preterm birth and term low birth weight), a multilevel generalized linear model for binary outcomes was considered due to the presence of the clustering effect, as described underneath in the model specification section. Multivariable multilevel model adjustment was done for both individual and community-level confounding variables.This study applied a multilevel analysis technique to account for the hierarchical/clustering nature of data. The clustering variable was kebele with a cluster size of 18. In this analysis, binary response variables (preterm birth and term low birth weight) were considered for multilevel modeling, independently. A two-level multilevel generalized linear model for binary outcomes was applied in which individuals (level 1) were nested within communities (level 2). The level 1 model represents the association of individual-level factors, including IPI, with the outcome variables. The level 2 model represents the influence of community-level confounding factors on the outcomes. Four models were fitted as follows:Model-I: It is an intercept-only model or model with no covariate inserted. It is used to check the variability among the communities (cluster-to-cluster variation) and used to give information to whether there is justifiable evidence to consider a random-effect model. Model-II: It is a multivariable model adjustment, containing only individual-level factors, including IPI. Model-III: It is a multivariable model adjustment, containing only community-level factors. Model-IV: It is a final adjustment model, containing both individual and community-level potential confounding factors.The effect of IPI (fixed-effect) on preterm birth and term low birth weight was expressed by using adjusted relative risk (ARR) with 95% confidence intervals and its public health impact was interpreted using attributable fraction (AF) and population attributable fraction (PAF). AF and PAF are calculated from the adjusted RR .The measures of variation (random-effects) were reported by using Intra-class (community) Correlation Coefficient (ICC) which explains the percentage of variation by community-level factors (level 2). Proportional Change in community Variance (PCV) was also used to express the percentage of changes in the community-level variance between the null model (model-I) and the successive models.A total of 2578 pregnant women were followed up until delivery. Of these, 291%) of them were lost of follow-up  and their pregnancy outcomes could not be ascertained. Of 29 lost of follow-up, 14 were from exposed and 15 from unexposed groups. The pregnancy outcome was ascertained for 2549 study participants. Of them, 235 had a preterm birth, 96 had term low birth weight and 47 had perinatal deaths. One woman has spontaneous abortion before 28 weeks of gestation, and she was not followed up anymore  than those who had IPI 24–60 months (Table P < 0.05) and term low birth weight across the communities . The ICC indicated that 14.41% of the variability in the risk of preterm birth and 18.83% of the variability in the risk of term low birth weight were due to community-level factors. In the final model (model-IV), the community-level variance remains significant (P < 0.05) even after controlling for both the individual and community-level factors. The ICC value of 9.31% in Table The null model (Model-I) showed that there was significant variability in the risk of preterm birth across the community  more likely to have a preterm birth as compared to women who had a pregnancy from 24–60 months  of preterm birth was attributed to the IPI < 18 months. In the study population, 9%  of preterm birth was attributed to IPI < 18 months.After adjustment for both individual and community-level confounding factors, IPI < 18 months was found to increase the risk of term low birth weight. Women who had a pregnancy within 18 months after a preceding live birth were two times  more likely to deliver a term low birth weight baby as compared to women who had a pregnancy from 24–60 months. IPI 18–23 months did not show significant association with term low birth weight  of term low birth weight was attributed to the IPI < 18 months. In the study population, 21%  of term low birth weight was attributed to IPI < 18 months.Collinearity diagnostic test was done for age and age at first childbirth using variance inflation factor. The maximum variance inflation factor value was 1.12, which is close to 1 or less than 10, suggesting that there was no multicollinearity problem. Thus, both variables retained in the adjusted model.As indicated in Tables In the multivariable model, controlling for potential confounding variables, IPI under 18 months was found to increase the risk of perinatal deaths. Accordingly, women who had a pregnancy within 18 months after the preceding live birth were nearly four times  more likely to have perinatal deaths relative to those who had a pregnancy from 24–60 months  of perinatal deaths were attributed to the IPI < 18 months. In the study population, about 41%  of perinatal deaths was attributed to the IPI < 18 months.In this study, IPI < 18 months was found to increase the risk of preterm birth, term low birth weight and perinatal deaths as compared to IPI 24–60 months. IPI 18–23 months has shown no significant association with the three adverse perinatal outcomes.The risk of preterm birth was higher for women with IPI under 18 months. This study suggest that about 26% of preterm births among multiparous women whose last birth was a live birth and who had an IPI < 18 months was attributed to the IPI under 18 months, which could be prevented with the removal of IPI under 18 months. In the study population (multiparous women whose last birth was a live birth and who had an IPI < 60 months), about 9% of preterm birth was attributed to the IPI < 18 months that could be prevented if IPI < 18 months did not exist. The link between IPI under 18 months and preterm birth is physiologically plausible. Shorter intervals between pregnancies might have resulted in a shorter time to recover from the abnormal conditions that happened during the preceding pregnancy and childbirth such as time to recover from the abnormal remodeling of the uterine blood vessels, which is linked to preterm premature rupture of fetal membranes and subsequent preterm births , 27–29. In this study, IPI under 18 months was found to increase the risk of term low birth weight than the IPI 24–60 months. This study revealed that about 54% of term low birth weight was attributed to IPI under 18 months which could be prevented if the IPI under 18 months did not exist in this group (multiparous women whose last birth was a live birth and who had an IPI < 18 months). Similarly, about 21% of term low birth weight could be prevented with the removal of IPI < 18 months in the study population (multiparous women whose last birth was a live birth and who had an IPI < 60 months). The results suggest that increasing IPI to at least 18 months have advantages in increasing the weight of a baby at birth that also helps to increase survival at later ages. This association seems physiologically plausible and supports the hypothesis that short IPIs are linked to maternal depletion syndrome or pregnancy-breastfeeding overlaps that deplete maternal resources via breastfeeding for the child already born and trans-placental sharing for the fetus in the womb . This, iIn this study, a higher risk of perinatal deaths was observed when IPI was under 18 months relative to IPI 24–60 months. This study reported that about 74% of perinatal deaths were attributed to IPI under 18 months that could be prevented if the IPI under 18 months did not exist in this group (multiparous women whose last birth was a live birth and who had an IPI < 18 months). About 41% of perinatal deaths could be prevented if IPI < 18 months did not exist in the study population (multiparous women whose last birth was a live birth and who had an IPI < 60 months). The exact mechanism by which short IPI results in perinatal deaths remained unclear. However, perinatal deaths might be related to the effect of IPI on preterm birth and low birth weight, as babies born preterm commonly have a low birth weight, making them unable to sustain breathing during labor and delivery and thus likely to die . Babies This study suggests that increasing IPI to 24–60 months has health advantages and improves the health or wellbeing of the fetus/baby in the womb and immediately after delivery. It was also reported that longer intervals improve neonatal and child survival thereafter. Adequate IPI gives a resting time to women to recover from lactation stress, lost nutrients like folic acid and iron, and helps to improve maternal health status and birth outcomes in the subsequent pregnancies. IPI is a modifiable risk factor of preterm birth, low birth weight and perinatal deaths. Nowadays, feasible interventions like modern contraception are available. Modern contraceptive methods are the ideal tools that we have at hand to space pregnancies to optimal duration. Increasing IPI to optimal duration  can be achieved by improving the utilization of those available modern contraceptive methods by overcoming the barriers to use such as lack of access, fear of side-effects, misconceptions, lack of decision-making power of women, lack of male involvement, etc. Family planning programs are also expected to give due emphasis to the importance of spacing pregnancies and risks such as preterm birth, low birth weight and perinatal deaths when the intervals between pregnancies are inadequate. Postnatal care might be an ideal time to counsel and initiate postpartum contraceptive utilization, including immunization visits, as these periods are a crucial time for addressing many clients, including the husband. Improving the utilization of long-acting contraceptive methods, which have a longer duration of protection than short-acting methods, may aid in achieving optimal IPI. This could be addressed through community-based development programs, such as health extension programs, in addition to health facility-based services. During the postnatal period, the risk of pregnancy might be higher due to sexual initiation since menses was not returned and couples might believe that the lactation amenorrhea method is sufficient. Women who get pregnant again after a live birth might go for an abortion, which risks bleeding and death. Thus, increasing IPI improves maternal health in addition to perinatal outcomes.Despite the attempts made to minimize, however, this study might have limitations that the target audience needs to consider during the interpretations. Firstly, we based on women’s recall about the dates of the last childbirth and the women’s last menstrual period to calculate the IPIs, some biases related to recalling might have occurred. Secondly, although we used a multisite population-based study to reduce selection bias, still some women might have not been included in the study. Thirdly, as this study relied on community-based data collection we couldn’t collect data about previous adverse pregnancy outcomes such as history of preterm birth and low birth weight. This might have affected the estimates somehow. Fourthly, the association of IPI with perinatal deaths (rare condition) lacks precision due to small sample size. Readers need to consider this during interpretation. Despite these potential limitations, this study has strong sides: firstly, it was a multisite community-based study that provides more informative incidences of the outcomes. Secondly, it is a prospective cohort study that can elucidate the temporal relationship between exposure and the outcomes than other observational studies. Thirdly, we have also considered the effect of clustering for potential unobserved heterogeneity (cluster dependency) using a multi-level generalized linear modeling (mixed effect) for preterm birth and term low birth weight. Thus, this yields more accurate or unbiased estimates of the parameters such as variance, standard errors, and confidence intervals. Considering the aforementioned limitations, the findings of this study can be generalized for similar populations and contexts.Inter-pregnancy interval under 18 months has a higher risk of adverse perinatal outcomes than inter-pregnancy intervals 24–60 months. Short inter-pregnancy interval is a modifiable risk factor of adverse perinatal outcomes. Attention should be given for spacing pregnancies. Preventive measures like improving the utilization of modern contraceptive methods in the community could help in reducing the risk of adverse perinatal outcomes.Additional file 1: Additional Figure 1. Theoretical framework for the effect of inter-pregnancy intervals on preterm birth, term low birth weight and perinatal deaths, and potential confounding variables.


The cumulative pregnancy and live birth rates for three AI-D cycles were 41.01% and 32.42%, respectively, higher than the rates for one or two AI-D cycles. The multiple birth and birth defect rate of AI-D was lower than that of IVF-D significantly. IVF-D mean cost per couple was higher than that of AI-D , with a mean cost difference of CNY21,513 . The mean costs per live birth cycle for IVF-D and AI-D were CNY49,411 and CNY31,246, respectively. Conclusion: AI-D is more cost-effective and poses a lower risk for infertility couples than IVF-D, and patients should undergo three AI-D cycles to obtain the highest success rate.Purpose: To evaluate the effectiveness of donor in vitro fertilization (IVF-D) and donor artificial insemination (AI-D) in clinical outcomes, risks, and costs. Methods: This study analyzed the cycle changes and clinical outcomes in 20,910 IVF-D and 16,850 AI-D cycles between 2013 and 2021 in the Reproductive and Genetic Hospital of CITIC-Xiangya. A cost-effectiveness analysis was performed to evaluate the costs per couple and per live birth cycle in the two treatment groups. Results: IVF-D had higher pregnancy and live birth rates than AI-D ( It was reported that the incidence of infertility in China has risen from 12 to 18% between 2007 and 2020 , and live birth rate . AI-D and IVF-D had similar total miscarriage rates. The detailed clinical outcomes of IVF-D and AI-D are summarized in p < 0.005). The cumulative pregnancy and live birth rates for three AI-D cycles were 41.0 and 32.4%, respectively. Similar pregnancy and live birth rates following AI-D were noted when more than three cycles were used. Interestingly, the miscarriage rate following AI-D did not change with the increase in cycle number.Compared to AI-D, IVF-D had a higher pregnancy rate  and birth defect rate . The details are shown in In this study, the risk index of IVF-D and AI-D was mainly multiple birth and birth defect rate. Compared to AI-D, IVF-D resulted in significantly higher multiple birth rate [24.7 vs. 1.9%; p < 0.001), with a mean cost difference of ¥ 21,513 . The respective mean costs of IVF-D and AI-D were CNY42,295 and CNY25,743 per pregnancy and CNY49,411 and CNY31,246 per live birth  is the first human sperm bank established in China. It has provided sperm donation services to over 80 reproductive centers in 23 provinces, municipalities, and autonomous regions across the country . This stFor patients, the choice of ART depends mainly on the clinical outcomes and cost-effectiveness of the various methods. This research found that the clinical pregnancy and the live birth rates following IVF-D were higher than following AI-D, with respective ratios of 2.92:1 and 3.08:1. The difference in the live birth rate was larger than the previously reported 2.35:1 ,12,13. Fwww.nice.org.uk/guidance/cg15, accessed on 13 October 2022). In China, 3–4 IUI cycles are recommended for women with unexplained infertility aged <40 years, and IVF is considered if unsuccessful [Although the pregnancy rate following IVF-D was higher than following AI-D in this study, some researchers suggested that IVF and IUI had similar clinical outcomes. A recent randomized controlled trial (RCT) comparing the pregnancy outcomes of IVF with a single embryo transfer and IUI with ovarian stimulation in couples diagnosed with unexplained or mild male subfertility found similar live birth and clinical pregnancy rates in both treatment groups . Anotherccessful ,19. FurtIVF is more invasive than IUI, causing a higher patient burden. According to our findings, IVF-D resulted in higher multiple birth and birth defect rates than AI-D, although the small difference in birth defect rates might not be clinically significant. These results are presumably because more than one embryo is normally transferred during IVF cycles . A retroWhen evaluating treatment effectiveness, we need to focus not only on the clinical outcomes but also on the costs. The mean costs per couple  and per live birth cycle  for IVF-D were significantly higher than for AI-D. AI-D was more cost-effective than IVF-D. Similarly, many studies have shown that IUI was more cost-effective than IVF [http://www.nhc.gov.cn/, accessed on 14 October 2022), resulting in a decrease in the semen supply traffic. Second, the increase in the application of the testicular sperm aspiration and extraction techniques in patients with nonobstructive azoospermia could deliver testicular sperm for ART, avoiding the need for donor sperm.Interestingly, our study found that the total number of IVF-D and AI-D cycles has significantly declined over the years, while the total ART cycles have increased at the Reproductive and Genetic Hospital of CITIC-Xiangya . We thinThe current study had some limitations. First, as a retrospective study, we could not compare the cost-effectiveness of three AI-D cycles and one IVF-D cycle. Second, the data on birth defects were provided by reproductive centers, following the dictation of the donor semen recipient, possibly affecting the results. Finally, our findings are not based on the general male population; sperm donors were selected for their better sperm quality, and further studies of this type are needed. On the other hand, we did not calculate the cost of fresh and frozen embryos for IVF-D, because the cost of frozen embryo cycles was only a small part of the total cost of IVF-D; it did not affect the conclusion of the study. Furthermore, due to the principle of double blindness between sperm donors and recipients in China, we cannot collect more information about patients.To our knowledge, this was the first study to compare the clinical outcomes and cost-effectiveness of IVF-D and AI-D. Furthermore, our retrospective analysis was based on the feedback data of over 80 reproductive centers across 23 provinces in China, which make our findings highly reliable.In conclusion, although the pregnancy rate following IVF-D was higher than that following AI-D, AI-D had a lower multiple birth rate and lower costs per couple and live birth. Therefore, AI-D is more cost-effective and poses a lower risk for couples with infertility than IVF-D. Patients with infertility should undergo three AI-D cycles to obtain the highest success rate.


Via physicochemical and electrochemical characterizations, we demonstrate that this peculiar electrolyte formulation weakens the electric double layer repulsive force, thus, favouring dense metallic zinc deposits and regulating the charge distribution at the zinc metal|electrolyte interface. When tested in Zn||VS2 full coin cell configuration (with cathode mass loading of 16 mg cm−2), the electrolyte solution containing the lanthanum ions enables almost 1000 cycles at 1 A g−1 (after 5 activation cycles at 0.05 A g−1) with a stable discharge capacity of about 90 mAh g−1 and an average cell discharge voltage of ∼0.54 V.Aqueous zinc batteries are appealing devices for cost-effective and environmentally sustainable energy storage. However, the zinc metal deposition at the anode strongly influences the battery cycle life and performance. To circumvent this issue, here we propose the use of lanthanum nitrate (La(NO Zinc metal is a promising anode material for aqueous secondary batteries. However, the unfavourable morphologies formed on the electrode surface during cycling limit its application. Here, the authors report the tailoring of the surface morphology using a lanthanum nitrate aqueous electrolyte additive. In aqueous electrolytes, the electrodeposition of hexagonal close-packed Zn metal has a strong propensity to form hexagonal platelets, which generates porous Zn depositions with irregular morphologies7. Such a porous structure is bound to exacerbate the chemical corrosion during the repeated plating and stripping of the Zn-metal phase due to the increased exposure of Zn electrodes to the electrolytes. The loose Zn particles with irregular morphology also cause the loss of electrical contact between the deposits and substrates and further deteriorates the reversibility of Zn electrodes4. What is worse, the dendritic Zn particles with irregular morphology may easily pierce the separator and lead to short circuits of batteries8.Despite the advantages of aqueous Zn-based batteries  using substrates with a low lattice mismatch and low affinity to lock the crystal orientation for the uniform Zn electrodeposition12; (3) increasing the driving force for the nucleation of Zn deposits to induce the uniform distribution of Zn-metal nuclei13. However, most of the above approaches rely on the modification of the Zn electrodes or current collectors, which decrease the overall energy density of the cells16. Besides, the long-term cycling of Zn electrodes under conditions of high depth of discharge (DOD) and/or high areal capacity of Zn remains challenging4. It is highly desired to explore new solutions to enable high effective Zn deposition without sacrificing the energy density.To induce uniform Zn deposition, several strategies have been proposed: (1) constructing artificial interface layers to restrict the Zn crystal growth and protect the Zn metal electrode from detrimental reactions with the aqueous electrolyte19. It is acknowledged that the morphology of the deposited Zn is related to multiple factors, including the intrinsic crystal anisotropy, electrolytes, substrate chemistry and geometry22 The process of Zn electrodeposition includes the desolvation and reduction of the Zn2+ ions, and the following formation and growth of the nucleus on conductive substrates. The final morphology of deposited metal is related to both the structure of as-formed grain crystals, which are observed as irregular hexagonal flakes for Zn, and the interactions between them23. Based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the interactions between Zn deposits in aqueous electrolytes are mainly related to the van der Waals (VDW) attractive force and the electrostatic repulsion due to the electric double layer (EDL) of counterions 27. Theoretically, by reducing the Debye length, the EDL repulsion force between two charged particles could be reduced. Here, we introduce La3+ ions, which serve as high-valence competitive ions to decrease the Debye length33, to the aqueous ZnSO4 electrolytes. The electrochemical and morphology characterizations confirmed the presence of the insert La3+ ions weakens EDL repulsive force between the Zn deposits, changes the preferred orientation of Zn deposits, and results in dense and compact Zn coherent electrodeposition. With La3+-modified electrolyte, the corrosion rate (the speed of corrosion loss) of Zn electrodes is significantly relieved with the corrosion current  decreased from 421.6 to 6.3 μA cm−2,34 enabling a high average Coulombic efficiency of > 99.9% for 2100 plating/stripping cycles. At a current density of 10 mA cm−2 and DODZn of 80%, the Zn||Zn cell with the modified electrolyte exhibited a stable Zn deposition for ~160 h. Benefitting from the stale Zn anodes, the Zn||VS2 cell in La3+-modified electrolyte with a limited Zn supply (11.6 mAh cm−2) and a high-loading VS2 cathode (16.0 mg cm−2) delivers a stable discharge capacity of about 90 mAh g−1 and an average cell discharge voltage of ~0.54 V. The as-proposed strategy demonstrates the importance of the thickness of EDL on the electrodeposition behaviors of Zn2+ ions and might also be applicable for other metal anodes.Based on the Poisson-Boltzmann (PB) model, the EDL repulsive force between the negatively-charged surfaces of Zn deposits is mainly influenced by the thickness of the EDL, which is known as the Debye length (1/3+-modified electrolyte (La3+-ZS) was prepared by dissolving La(NO3)3 into ZnSO4 solution (ZS), a common electrolyte for aqueous Zn-ion batteries. To verify the effects of La3+ on Zn deposition, we firstly compared the plating/stripping performance of Zn||Zn cells in ZS and La3+-ZS electrolytes with a current density of 1 mA cm−2 and an areal capacity of 1 mAh cm−2  and analyzed the morphology of the cycled Zn electrodes by a scanning electron microscopy (SEM). As the result shown in Fig. 5. In addition, this structure also leads to more side reactions between the Zn electrode and electrolyte due to the exposed surface, and thus more by-products accumulation. In comparison, after being cycled under a same test condition, the Zn electrode with La3+-ZS electrolyte displays a dense surface with the deposited Zn particles closely connected with each other 3 into the ZS electrolyte induces dense Zn electrodeposition and enhances the utilization of Zn foil.To figure out how the Laher Fig. . Figure eft Fig. . ConsideZn) significantly affects the cycling life and the overall specific energy of the full cell4. The plating/stripping performance of the symmetrical Zn||Zn cells under different DODZn was tested using thin Zn electrodes  with ZS and La3+-ZS electrolyte. Figure Zn = 80% . Under such a high DODZn, the control Zn||Zn cell with ZS electrolyte showed a sharp voltage increase at the end of the initial stripping/plating process and failed after 3 h of cycling 3 into ZS electrolyte.It is known that the Zn deposits in ZS electrolyte tend to exhibit a hexagonal-platelet morphology due to the lower thermodynamic free energy of the exposed (002) planem−2 Fig. . Here, tets Fig. , the dec3+-ZS electrolytes was further characterized by grazing incidence X-ray diffraction (GIXRD), a powerful tool to investigate the texturing and orientation anisotropy of thin film. As the result shown in Fig. 3+-ZS electrolyte display a relatively weaker (002) peak. Quantitatively, the relative intensity ratio of peak (002) (I(002)) to that of peak (100) (I(100)) decreases from 1.4 to 0.92, indicating that the reduced (002) planes for the Zn deposits in La3+-ZS electrolyte. Considering the hcp structure of Zn 3 additive, we prepared another control electrolyte (marked as NO3−-ZS), which has the same NO3− concentration as that of the La3+-ZS electrolyte (0.0255 m), by adding Zn(NO3)2 to the ZS electrolyte. The cycling stability of the Zn||Zn cells with ZS, La3+-ZS, and NO3−-ZS electrolytes was compared with a current density of 1 mA cm−2 and an areal capacity of 1 mAh cm−2 . Such results imply that the improved cycling stability of the Zn electrodes in La3+-ZS electrolyte is mainly attributed to the La3+ ions. To determine how the La3+ ions affect the Zn plating/stripping behaviors, we further investigated the cycled Zn electrodes in ZS and La3+-ZS electrolytes with energy-dispersive X-ray spectroscopy (EDS). The corresponding SEM images are shown in Supplementary Fig. 3+-ZS electrolytes. As the results shown in Fig. 3+-ZS electrolyte suggests that the La3+ ions in La3+-ZS electrolyte are not reduced or involved in the formation of the by-products. The inert nature of La3+ ions guarantees the durability of the La3+-ZS electrolyte during long-term cycling. Here, the similar CPS amounts  in a three-electrode cell set-up, where the working electrode and the counter electrode both are Zn foils, and the reference electrode is an Ag/AgCl electrode  soon after the overpotential was applied, implying the activation of all the nucleation sites. In contrast, the current density for the cell with La3+-ZS electrolyte is characterized by prolonged activation time, indicating that the number of nuclei increases gradually with time and the progressive nucleation is governing during Zn deposition in La3+-ZS electrolyte42. It is also noticed that the steady current density in ZS electrolyte (~−26 mA cm−2) is higher than that in La3+-ZS electrolyte (~−22 mA cm−2). The differences in the nucleation mechanisms and steady current densities could be ascribed to the adsorption of the La3+ ions on the surface of the Zn electrodes, which decrease the number of the active nucleation sites and slow down the formation of the nuclei in La3+-ZS electrolyte.The Zn deposits growth mechanism in ZS and La48. According to the Langmuir isotherm, the relationship between the equilibrium coverage (θ) and the concentration (c) of the adsorbents in the bulk solution follows Eq. 3 in La3+-ZS electrolyte is only 0.0085 m, much less than that of ZnSO4 (2 m), the equilibrium adsorbent coverage θ could be regarded as the same for the Zn electrodes in ZS and La3+-ZS electrolytes, which means the current density (j) of the CA curves is proportional to the number of the adsorbed Zn2+ ions. In other words, the lower current density signifies less Zn2+ ions are adsorbed on the electrode in La3+-ZS electrolyte, which is the result of the completive adsorption of inert La3+ ions. Besides, the Zn nucleation in La3+-ZS electrolyte shows larger polarization voltage than that in ZS electrolyte  plane 34, implying a lower tendency of corrosion of Zn electrodes. In addition, the corrosion current (Icorr) of Zn electrodes is reduced from 421.6 μA cm−2 in ZS electrolyte to 6.3 μA cm−2 in La3+-ZS electrolyte, implying that the corrosion was inhibited by 98% with the addition of La3+ based on the Eq.  plane  and a high-loading cathode (8.0 mg cm−2) at a specific current of 0.1 A g−1 after 5 activation cycles at 0.05 A g−1. As the results displayed in Fig. 2 cell with ZS electrolyte shows a rapid capacity decay and failed after 30 cycles. Whereas the cell with La3+-ZS electrolyte remains a discharge capacity of 108 mAh g−1 after 100 cycles. The normalized discharge/charge profiles of the Zn||VS2 cell at the 20th cycle were compared in Fig. 3+-ZS electrolyte. In addition, the voltage hysteresis of the cells in La3+-ZS electrolyte decreases slightly from 118 mV in the 6th cycle to 101 mV in the 24th cycle, whereas the ones in ZS electrolyte increases gradually with cycles  with a high average CE of 99.89%. In comparison, the Zn||VS2 cell with ZS electrolyte faded quickly and failed in less than 400 cycles. Furthermore, compared with that of the one using ZS electrolyte, the cycling performance of the Zn||VS2 cell with a limited Zn supply (11.6 mAh cm−2) and a high-loading VS2 cathode (16.0 mg cm−2) using La3+-ZS electrolyte showed significantly improved cycling stability and higher average discharge voltage (the voltages of cells at medium discharge capacity) 0.54 V vs. 0.49 V at a high areal current density of 16.0 mA cm−2 during the long-term cycling , and stable Zn||VS2 coin cell performance were realized.In summary, by introducing high-valence La4) was prepared by dissolving 17.25 g of ZnSO4  into 30 ml of deionized (DI) water. The La3+-ZS electrolyte (2 m ZnSO4 and 0.0085 m La(NO3)3) was prepared by adding 110.4 mg of La(NO3)3  into 30 mL of ZS solution. To inquire the role of NO3−, NO3−-ZS electrolyte with a same concentration of NO3− as La3+-ZS was prepared by adding 113.8 mg of Zn(NO3)2  into 30 mL of ZS solution.The ZS electrolyte  was added to a 45 ml of 3 mmol NH4VO3 solution one by one with an interval time of 1 h under stirring. After being stirred for another hour, the as-received brown mixture was transferred into a 50 ml Teflon-lined autoclave and maintained at 180 °C for 20 h. After the reaction, the solid product was collected by centrifuging and washing with DI water and ethanol thoroughly and dried in a vacuum oven at 50 °C overnight. Finally, the as-collected black powders were annealed in N2 at 180 °C for 8 h to obtain the VS2 powders.VSα1 radiation (λ = 1.5406 Å) from 10° to 90°. Grazing incidence X-ray diffraction (GIXRD) patterns were collected from 35 to 47° on a Rigaku SmartLab X-ray diffractometer with a Cu-Kα1 radiation with a step size of 0.0001°. All the electrode samples were collected by disassembling the Zn||Zn cells after a certain number of cycles at different currents. After being rinsed in DI water and dried in the air, the sampled electrodes were transferred into the SEM and XRD equipment for the morphology analysis of Zn deposits.The morphologies and structures of the samples were characterized by field emission scanning electron microscopy  equipped with energy-dispersive X-ray spectroscopy (EDS). X-ray diffraction (XRD) patterns were recorded with a Bruker-AXS microdiffractometer (D-8 ADVANCE) using Cu-K2 electrodes were prepared by a blade-cast method. Briefly, the VS2 powders, acetylene black carbon, and polyvinylidene fluoride (PVDF) were mixed with a weight ratio of 7: 2: 1 in N-methyl-2-pyrrolidone (NMP) with an electric mixer . Then, the as-prepared slurry was blade-casted onto a Ti foil . After being dried in a vacuum oven at 50 °C overnight, VS2 electrodes were obtained by cutting the above Ti foil into circular sheets with a diameter of 8 mm. The CR-2032 coin cells were assembled using glass fiber  as separators, Zn plates or VS2 electrodes as the working electrodes, and Zn plates , Ti foils, or carbon papers  as the counter electrodes, 100 μl of electrolytes were added to each cells. For the electrochemical characterizations of the Zn||VS2 cells with a limited Zn supply , the areal mass loading of VS2 electrodes was ~8.0 mg cm−2, while the number is ~1.0 mg cm−2 for all other Zn||VS2 cells. The CE tests was measured with Zn||Ti (or Zn||C) cells with a Zn deposition of 1.0 mAh cm−2 (2 mA cm−2 for 0.5 h) and a charge cut-off voltage of 0.4 V. All the above tests were performed on a Neware Battery Tester. To test the corrosion rate of Zn foil, a three-electrode cell was constructed using Zn foil as the working electrode, Pt wire  as the counter electrode, and Ag/AgCl electrode as the reference electrode and tested on an electrochemical workstation . The efficiency of protection (η%) for Zn electrodes in a La3+-ZS electrolyte was calculated by using the values of the corrosion current Icorr shown as the Eq. All the electrochemical measurements are conducted in air, and the temperature is controlled at 25.0 ± 2.0 °C. The VS−1 were recorded electrochemical workstation . The Zeta potential was collected on a Zeta potential analyzer .The linear polarization curve, chronoamperometry (CA) , and cyclic voltammetry (CV) curves at a scan rate of 0.1 mV sSupplementary information


Low birth weight (LBW), defined as a birth weight <2,500 g, is a major public health concern worldwide. Globally, in 2015, 20.5 million infants with LBW were born, accounting for 14.6% of all births, according to data compiled by United Nations International Children's Emergency Fund . To manaIn 2019, 9.4% of babies born in Japan were LBW . For exaAlthough early gestational age  and multThe present study aimed to observe the 20 year trend between 2000 and 2019 in the prevalence of LBW in singleton, full-term births in Japan and conduct joinpoint regression to analyze trends in detail. It is hoped that this study will provide new insights that will prove useful for maternal and child health.This study was a retrospective, nationwide, population-based, observational study of vital statistics published by the Japanese government . Secondagestational age multiple pregnancies, ages of the father and mother, and place of birth. These data are electronically registered and systematized by the municipality as vital statistics data.The number of births and LBW newborns by gestational age and sex were obtained from annual vital statistics population data collected by the Ministry of Health, Labor and Welfare based on birth certificates. The dataset used in this study showed only the annual number of births according to gestational age, sex, and birth weight, and did not include information on individuals. In Japan, birth certificates are issued by obstetricians and midwives in hospitals and clinics at the time of delivery, and these data are reported to the mayor of the municipality. The birth certificate contains information such as sex, birth weight, * 100.Outcome variables for this study were the prevalence of LBW in singleton, full-term births in Japan. We calculated the prevalence of presented variables as the percentage  We limited our analysis to singleton, full-term births to avoid bias from multiple births and gestational age as risk factors for LBW. Based on birth weight and gestational age, we defined LBW in full-term birth as a birth weight of <2,500 g at a gestational age of ≥37 weeks.years (as the independent variable) in which significant changes in prevalence rate occurred over the study period, and amount of change as the annual percentage change in rate per year. We allowed up to four joinpoints and identified any difference from no change in each segment, with values of p < 0.05 considered statistically significant. Stata for Mac version 15  was used for all other statistical analyses.Trends in the prevalence of LBW from 2000 to 2019 were analyzed using joinpoint regression analysis. This method connects several different line segments, thus allowing for succinct characterization of changes in a trend over time . The Joibased on the use of published, public-domain data.The Ethics Committee for Human Subjects Research at Shokei Gakuin University waived the requirement for ethical approval A total of 21,061,052 births were recorded during the study period, of which 1,976,911 (9.39%) were LBW. Among these, 1,066,959 (53.97%) were singleton, full-term births. To the best of our knowledge, the current study is the first to quantify upward and downward trends in the prevalence of singleton, full-term LBW in Japan. Joinpoint regression analysis was performed in a large, long-term, national dataset covering almost all births for the period from 2000 to 2019. The first 10 years showed an upward trend, and the second 10 years showed a downward trend, with peak prevalence occurring in 2010 for both males (4.46%) and females 6.89%). Joinpoint analysis also revealed the statistical significance of change points for the start points of decreases in the prevalence of LBW in singleton, full-term births . Takemoto et al. studied singleton births between 1979 and 2010 using vital statistics data and reported a greater increase in the prevalence of LBW among full-term births in the studied period, from 2.7% in 1979 to 5.3% in 2010 9%. Joinp, 13. Howhospitals per million inhabitants, and ratios of healthcare workers, midwives per 1,000 inhabitants , dietary, and socioeconomic factors are likely to have affected these trends. An ecological study by Erasan et al. reported that factors influencing increasing LBW prevalence in OECD countries between 2000 and 2015 were healthcare coverage, public health system coverage, such as abitants . Erasan abitants , 15. In The present study showed several limitations that need to be considered when interpreting the results. First, as we used governmental reports that provided only annual aggregated statistics for sex, gestational age, and birth weight, there was no source of individual-level data. In addition, in contrast to similar previous studies, we could report only crude data regarding the prevalence of LBW, without adjusting for maternal age , pre-preThis study used joinpoint analysis to demonstrated that the trend in the prevalence of Japanese LBW among the population limited to singleton, full-term births has been decreasing since around 2010. This findings runs counter to existing evidence based on all births, including preterm and multiple births, that the prevalence of LBW has been consistently increasing. Further studies are needed to confirm factors affecting changing trends in the prevalence of LBW.https://figshare.com/s/444100c4a0f23b01aac3.Publicly available datasets were analyzed in this study. This data can be found here: Material preparation, data collection, and analysis were performed by TM. The first draft of the manuscript was written by TM. All authors contributed to the study conception and design, commented on previous versions of the manuscript, and have read and approved the final version of the manuscript.This work was supported by a JSPS KAKENHI grant (No. 19K19440) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.