To evaluate the capacity of fetal Doppler, maternal, and obstetriccharacteristics for the prediction of cesarean section due to intrapartumfetal compromise (IFC), a 5-min Apgar score < 7, and an adverse perinataloutcome (APO), in a high-risk population.This was a prospective cohort study involving 613 singleton pregnant women,admitted for labor induction or at the beginning of spontaneous labor, whounderwent Doppler ultrasound within the last 72 h before delivery. Theoutcome measures were cesarean section due to IFC, a 5-min Apgar score <7, and any APO.p = 0.03 andp < 0.0001, respectively). A UA RI > the 95thpercentile and a cerebroplacental ratio (CPR) < 0.98 were also found tobe predictors of cesarean section due to IFC. Gestational age and a UA RI> 0.84 were found to be predictors of a 5-min Apgar score < 7 fornewborns at < 29 and ≥ 29 weeks, respectively. The UA RI and CPRpresented moderate accuracy in predicting an APO, with areas under the ROCcurve of 0.76 and 0.72, respectively.We found that maternal characteristics were neither associated with norpredictors of an APO. Abnormal umbilical artery (UA) resistance index (RI)and the need for intrauterine resuscitation were found to be significantrisk factors for cesarean section due to IFC (A high UA RI appears to be a significant predictor of an APO. The CPR seemsto be predictive of cesarean section due to IFC and of an APO in latepreterm and term newborns. In most cases, IFC occurs in low-risk pregnancies, makingadverse perinatal outcomes (APOs) difficult to predict.Acute fetal compromise is one of the leading causes of perinatal morbidity andmortality worldwide. As well as being a major cause of fetal death, a reduction inthe oxygen supply for the conceptus can lead to relevant neonatalcomplications,5. Technologiescomplementary to CTG were developed to reduce false-positive rates and avoidunnecessary interventions in cases of suspected fetal compromise, although there arestill many uncertainties regarding the benefits of such technologies and technicaldifficulties related to their use, which hinder their introduction into clinicalpractice-10. When acute fetal compromise becomes established,various physiological changes, including the redistribution of the fetoplacentalblood flow, occur and behave as defense mechanisms; that is, attempts to maintainadequate oxygen levels in vital organs for fetal survival (the “brain sparing”effect). This phenomenon can be evidenced by cerebral blood flow Doppler,12, which can show a reduction in the resistance index (RI)of the fetal middle cerebral artery (MCA).Although electronic monitoring of the fetal heart rate (FHR), known ascardiotocography (CTG), is widely used in screening for IFC, its use has not reducedthe incidence of hypoxic-ischemic encephalopathy, probably due to its low positivepredictive value in diagnosing fetal hypoxia-16. Studies have shown that, in cases of in late-onset fetalgrowth restriction (FGR), there is an association between the brain sparing effectand the occurrence of an APO-19. However, this phenomenon is alate manifestation of fetal compromise, and, given its potentially harmfulconsequences, there is a need for methods that can detect signs of fetal blood flowredistribution earlier.Despite the seemingly beneficial role of the fetal brain sparing effect, some recentstudies have produced results that call into question its protective effect, whichcan be greater or lesser depending on the gestational age (GA) at which it occursand whether other hemodynamic parameters are normal or abnormal-25. Because it represents the ratiobetween the RI of the MCA and that of the umbilical artery (UA), the CPR can beabnormal even before the brain sparing effect has been identified. Nevertheless, studies evaluatingthe CPR and its association with the occurrence of an APO vary widely in terms ofmethodology and outcome measures. There is therefore insufficient evidence torecommend its introduction into clinical practice as a predictor of poor obstetricoutcomes and neonatal complications.For normal and FGR fetuses, the cerebroplacental ratio (CPR) has emerged as predictorof cesarean section due to IFC, an APO, and long-term neurologicalimpairmentThe objective of this study was to evaluate the capacity of fetal Doppler, as well asof maternal and obstetric characteristics, to predict, in a high-risk population,cesarean section due to IFC, a 5-min Apgar score < 7, and the occurrence of anAPO.This was a prospective cohort study that included high-risk pregnant women admittedfor labor induction due to maternal conditions or pregnant women admitted at thebeginning of spontaneous labor . All patients wererecruited from the University Hospital of the Ribeirão Preto Medical Schoolof University of São Paulo (FMRP-USP), in the city of Ribeirão Preto,Brazil, in 2018. The facility serves approximately 1,800 high-risk pregnant womenevery year. The inclusion criteria were GA > 26 weeks at delivery; singletonpregnancy; fetus without congenital anomalies; and obstetric ultrasound within thelast 72 h before delivery. The following exclusion criteria were applied: structuralor chromosomal anomalies diagnosed in the newborn; transfer of the newborn toanother hospital; and failure to acquire data from the medical records. The studywas approved by the FMRP-USP Research Ethics Committee (Reference no. 14366/2009).All participating patients gave written informed consent.Of 1,167 eligible pregnant women, 554 did not meet the study criteria and wereexcluded, leaving 613 for analysis. The GA was determined on the basis of the lastmenstrual period and confirmed by a first trimester scan using the crown-rumplength, or by the head circumference measured in a second trimester scan, performedbetween weeks 14 and 20 of pregnancy.; single deepest vertical pocket (SDVP) of amnioticfluid; and the RIs ofthe UA and MCA on Doppler ultrasound. The UA was assessed at the level of umbilicalcord insertion into the placenta, and the RI was considered abnormal if the valuewas above the 95th percentile.The RI of the fetal MCA was assessed in a cross-sectional view of the fetal head atthe level of the origin of the MCA from the circle of Willis and was consideredabnormal if the value was below the 5th percentile. Flow velocity waveforms were obtained withoututerine contractions, fetal body movements, or maternal respiratory movements, whenthe FHR was normal. The UA and MCA were evaluated with color Doppler. The pulsedDoppler sample volume was < 3.0 mm, the insonation angle was < 30°, and thefilter was set at < 50 Hz. The CPR was calculated by dividing the RI of the MCAby that of the UA, and the resulting value was considered abnormal if <1.0.All ultrasound examinations performed before admission were conductedtransabdominally with a 4-8 MHz probe  by consultants with considerable experience in fetal medicine.The following parameters were measured: fetal biometry and estimated fetal weight(EFW), as described previously and the American College ofObstetricians and Gynecologists (ACOG) guidelines. If IFC was suspected, the pregnancies weremanaged in accordance with the ACOG guidelines. Indeterminate (category II) or abnormal (category III) FHRtracings, even after 10-15 min of intrauterine resuscitation, corresponded toIFC.Intrapartum electronic FHR analysis was carried out in accordance with the NationalInstitute of Child Health and Human Development guidelines. It is noteworthy that patients with absent or reversedend-diastolic velocity in the fetal UA or increased fetal ductus venosus pulsatilityindex undergo cesarean section at our institution. In addition, IFC was defined,according to International Federation of Gynecology and Obstetricscriteria, as a fetalbiophysical profile score ≤ 4 before delivery or a CTG result classified aspathological after delivery. However, the following were not considered indicationsfor preterm delivery or cesarean section: a CPR or MCA RI < the 5th percentile; aUA RI > the 95th percentile with positive end-diastolic velocity; the fetus beingcategorized as small for gestational age (SGA), with an EFW < the 3rd percentileor < the 10th percentile plus abnormal Doppler findings; and GA < 37weeks.Obstetric care was provided in accordance with the local guidelines, which are basedon the best available evidence.Variables of interest related to maternal characteristics, maternal history,ultrasound findings, intrapartum interventions, and newborn characteristics wereobtained from each pregnant woman at enrollment in the study and from medicalrecords. The following outcomes were considered: cesarean section due to IFC; a5-min Apgar score < 7; and any APO. The occurrence of an APO was defined as oneor more of the following: intraventricular hemorrhage; periventricular leukomalacia;hypoxic-ischemic encephalopathy; necrotizing enterocolitis; bronchopulmonarydysplasia; sepsis; admission of the newborn to the neonatal intensive care unit; andneonatal death. The local neonatology unit is a member of the Vermont Oxford Networkand therefore applies the diagnostic criteria established by the network for eachneonatal complicationp < 0.05 were considered statistically significant.The sample calculation was performed using Proc Power procedure in theStatistical Analysis System, version 9.3 .Continuous variables are presented as mean and standard deviation, whereascategorical variables are expressed as absolute and relative frequencies. Thechi-square test was employed to detect associations between qualitativevariables and outcomes. A binomial log regression model  was used in order to estimatethe crude and adjusted relative risks (RRs) for each variable in relation to theoutcomes. A conditional inference tree model was employed to determine the mostsignificant predictors for the outcomes, which allowed the use of quantitativeand qualitative variables, with R software, version 3.6.1. . Receiver operating characteristic (ROC)curves were constructed to evaluate the individual accuracy of each parameterfor predicting outcomes by calculating the area under the curve (AUC). Values ofThe final study sample comprised 613 singleton pregnant women: 542 (88.4%) admittedfor labor induction; and 71 (11.6%) admitted at the beginning of labor. The meanmaternal age was 28.4 ± 6.97 years , 319 (54.3%) of thepregnant women were obese, and the mean maternal weight was 90.3 ± 22.2 kg. The mean GA at delivery was 38 ± 3.2 weeks , the mean birth weight was 2,914 ± 813 g , and 179(29.2%) of the newborns were classified as SGA. The mean RI for the UA and the MCAwas 0.58 ± 0.10  and 0.73 ± 0.07 ,respectively. The mean CPR was 1.27 ± 0.27 , and the meanSDVP was 3.91 ± 1.81 cm .p = 0.004). During the study period, the overall rate ofcesarean section in our high-risk neonatology unit was 42.0%.p = 0.03; and RR = 3.77, 95%CI: 2.53-5.62, p < 0.0001, respectively). For a 5-min Apgarscore < 7, the risk factors were oligohydramnios  and prematurity . The variables considered significant risk factorsfor an APO were oligohydramnios , prematurity ,and cesarean section . TheEFW was not found to affect those results.In the multivariate analysis, an abnormal UA RI and the need for intrauterineresuscitation retained their significance as risk factors for cesarean section dueto IFC . For a 5-min Apgarscore < 7, the most relevant predictor was low GA at delivery. A 5-min Apgarscore < 7 was seen in 45% of the newborns at a GA < 29 weeks. It is essentialto highlight that in that group (n = 26), the pregnancies ended in labor inductionin four cases, spontaneous labor in four, and elective cesarean section due tochronic maternal disease in 19. However, for newborns at a GA ≥ 29 weeks, themost significant predictor of a 5-min Apgar score < 7 was a UA RI > 0.84. Inthe group with a fetal UA RI < 0.84 before delivery, the prevalence of thatoutcome was near zero.The conditional inference tree model showed that a GA < 34 weeks at delivery wasthe most significant predictor of an APO, which occurred in 85% of the newborns at aGA < 34 weeks, compared with 30% of those born at a GA of 34-36 weeks and 5% ofthose born at a GA > 36 weeks. The prevalence of an APO was 25% among thenewborns at a GA > 34 weeks with an abnormal CPR. Among the newborns with anormal CPR, oligohydramnios was a relevant predictor of an APO, which occurred in12% of those with oligohydramnios, compared with 2% of those with normal amnioticfluid volume. Among the newborns at a GA > 37 weeks, the prevalence of an APO wasnear zero. Two other factors were significant predictors of an APO among thenewborns at a GA < 37 weeks: an MCA RI < the 5th percentile; and cesareansection due to IFC. Among the preterm newborns with the brain sparing effect, theprevalence of an APO was 75% for those delivered by cesarean section, compared withonly 25% for those delivered vaginally. Among the preterm newborns without the brainsparing effect, the prevalence of an APO was 30% regardless of the mode ofdelivery.In the ROC curve analysis, all of the ultrasound variables presented poor performancein the prediction of cesarean section due to IFC and of a 5-min Apgar score < 7.However, an abnormal UA RI and an abnormal CPR presented moderate accuracy inpredicting an APO, with AUCs of 0.76 (95% CI: 0.69-0.81) and 0.72 (95% CI:0.65-0.77), respectively, whereas the other ultrasound variables all performedpoorly in the prediction of an APO.-23,36,37. In the presentstudy, a CPR ≤ 0.98 proved to be a significant predictor of cesarean sectiondue to IFC, regardless of the GA at delivery, and a CPR < 1.0 proved to be asignificant predictor of APO in newborns at > 34 weeks. Our results also showthat maternal characteristics were not predictors of any APO. In a prospective studyof women who gave birth to full-term fetuses, Fiolna et al. demonstrated that combiningmaternal characteristics with GA increased the accuracy of the prediction ofcesarean section due to IFC. However, the addition of the CPR did not improve thataccuracy. However, the features of our sample and the GAs at delivery are verydifferent from those of the Fiolna et al. sample.Our study was motivated by recent publications that showed an association between anabnormally reduced CPR and the occurrence of APOs, Valiño et al., and Stumpfe et al. in samples of FGR fetuses.However, it differs from those of Vollgraff Heidweiller-Schreurs et al., who demonstrated the superiorityof the CPR over UA Doppler in predicting cesarean section due to IFC. However, aspreviously mentioned, a CPR < 0.98 might also be a relevant predictor of thatoutcome, as demonstrated by other authors,24,42. Nevertheless, it is crucial to highlight thedifferences among the studies. In addition, our study has a major limitation, whichis the absence of pH results confirming neonatal acidosis. Furthermore, in theconditional inference tree model in which abnormal UA was shown to be a betterpredictor than the CPR, the ultrasound parameters were qualitative. Therefore, theuse of a CPR cutoff of 0.98 could have influenced the findings.Despite the potential associations of ultrasound variables with cesarean section dueto IFC, only an abnormal UA RI remained a significant risk factor in themultivariate analysis, cesarean section due to IFC having occurred in 55% of thecases in which the UA RI was abnormal, compared with only 10% of those in which itwas normal. That is in agreement with the findings of DeVore,43. However, this finding underscores the importance of the CPRas a predictor of the outcome, given that many of the pregnant women in whom IFC wassuspected had previously been pregnant with a fetus with an abnormal CPR.Although the fact that the need for intrauterine resuscitation was an importantpredictor of cesarean section due to IFC seems like an obvious finding, only 55% ofthe cases in which intrauterine resuscitation was performed ended in cesareansection because the FHR pattern of IFC persisted thereafter,44. Oligohydramnios was a risk factor for a 5-min Apgar score< 7 but was not found to be a significant predictor of that outcome in theconditional inference tree model. The comparison of these findings with those ofother studies was limited, because many authors have evaluated the associationbetween the amniotic fluid index and APOs considering only term or post-termpregnancies.There were difficulties in comparing our findings related to a 5-min Apgar score <7 with those of other studies because, in many of those studies, that outcome wasincluded as composite neonatal morbidity, APO, or a similar term. In addition, oursample of pregnant women was quite diverse, with fetuses of various GAs and growthpatterns. The variables considered risk factors for a 5-min Apgar score < 7 wereoligohydramnios and a GA < 37 weeks at delivery. The latter was a relevantpredictor of that outcome, which occurred in 45% of the newborns at a GA < 29weeks, regardless of the ultrasound findings. However, among the newborns at a GA≥ 29 weeks, the GA seemed to have a lesser effect and a UA RI > 0.84 was abetter predictor of a 5-min Apgar score < 7. Therefore, GA at delivery was thefactor that most influenced the neonatal outcome, especially when it was < 29weeks, as has also been shown in other high-quality studies,44, prematuritymight be predictive of an APO because of fetal organ immaturity. After week 34 ofgestation, the gain in survival and reduction in neonatal morbidity isminimal. Among allpreterm newborns (GA < 37 weeks) in the present study, the brain sparing effect(MCA RI < the 5th percentile) was a predictor of an APO and acquired greaterrelevance when the newborn was delivered by cesarean section. Although this findingseems inconsistent, it should be borne in mind that the brain sparing effect is,initially, a protective event in a fetus with hypoxemia. Fetuses with cerebral vasodilation are at lowerrisk of an APO in the early stages of hypoxia. In addition, our findings indicatethat, for fetuses with the brain sparing effect, the risks of performing a vaginaldelivery are outweighed by the benefits of that type of delivery in comparison withcesarean section.A GA < 37 weeks at delivery was confirmed as the most critical predictor of anAPO, especially for the newborns at a GA < 34 weeks, 85% of whom experienced anAPO, compared with 30% and 5% for those born at 34-36 and > 36 weeks,respectively. As previously discussed,41,47-49.However, there were major limitations to comparing our results with those of otherstudies of the topic. In many such studies, the reference values and CPR cutoffpoints were unclear, the GA limits were not stated, the features of the women andtheir pregnancies were not correctly presented, and the number of cases wasinsufficient to analyze the outcomes. One possible explanation for our finding is the fact that thebrains of late preterm and term fetuses are more sensitive to hypoxia than are thoseof preterm fetuses. In a studyof newborns at a GA of 35-37 weeks, Akolekar et al. found an association between the CPR and theoccurrence of an APO, although they showed that the CPR had low accuracy andrecommended caution in its use to predict that outcome.In our analysis of the newborns at a GA > 34 weeks, an abnormal CPR was associatedwith the occurrence of an APO, as demonstrated in previous studies.Finally, as shown in our ROC curve analysis of the predictive power of the ultrasoundvariables , the UA RI and CPR presented moderateaccuracy in predicting the occurrence of an APO. That is in contrast with thefindings that have been presented and discussed in other studiesIn summary, GA is still a relevant variable that should be considered when proposinga delivery modality. An abnormal UA RI is a significant predictor of APO, especiallyin third-trimester, high-risk pregnancies. The CPR has emerged as a possible toolfor predicting an APO, and, in our sample, it was found to be a predictor ofcesarean section due to IFC and of an APO in late preterm and term pregnancies.However, when evaluated separately, the CPR presented moderate accuracy inpredicting an APO. Therefore, its introduction into clinical practice should stillbe evaluated with caution.


Coronary artery bypass graft (CABG) pseudoaneurysms are a rare but often unrecognized clinical entity. They are prone to rupture and hemodynamic compromise and should therefore be on the differential in the appropriate patient. We present a case of a gentleman with a recent CABG surgery who presented with acute onset dyspnea and a large pleural effusion. Imaging revealed a saphenous vein graft pseudoaneurysm embedded in a mediastinal hematoma. Four weeks later, prior to planned stenting, the pseudoaneurysm had spontaneously closed. This case highlights an unusual acute presentation of a CABG pseudoaneurysm and a multidisciplinary approach to its management. Pseudoaneurysms of coronary artery bypass graft (CABG) vessels are rare, estimated to develop in <0.1% of grafts . Because1). This led to consultation with our cardiology and cardiothoracic surgery colleagues. The most likely explanation for the patient's presentation was a disruption in the SV graft pseudoaneurysm leading to a mediastinal hematoma and hemothorax. The patient was not a good surgical candidate given relatively recent CABG and his multiple medical co-morbidities. Ultimately, we decided to proceed with placement of an off-label covered stent across the site of the pseudoaneurysm. However, placement of an off-label covered stent required Institutional Review Board approval for emergent use. Although there was concern the pseudoaneurysm could further expand, the halted output from the chest tube as well as the patient's hemodynamic stability suggested that the pseudoaneurysm was contained. Because of this and the time required for approval of the stent, the patient was discharged with strict return precautions with plan for direct admission in three weeks for repeat left heart catheterization and placement of a covered stent across the pseudoaneurysm. The only medication change made on discharge was continuing to hold his apixaban for his atrial fibrillation given the risk of further expansion of his mediastinal hematoma. Repeat left heart catheterization three weeks after discharge showed a patent SV aorta-rPDA with spontaneous resolution of the pseudoaneurysm (2), thus precluding use of the stent. Intravascular ultrasound confirmed closure of the pseudoaneurysm, although a minimal remnant pseudoaneurysm could be seen. The patient was doing well at cardiology follow-up approximately two months later. Cardiac CT with three-dimensional angiography approximately three and a half months after initial presentation showed persistent resolution of the pseudoaneurysm, with a hematoma that had decreased in both size and density , diabetes mellitus, atrial fibrillation (on apixaban), chronic obstructive pulmonary disease, and three vessel CABG  approximately six months prior to presentation, presented with the acute onset of dyspnea while walking up a ramp at his home. The dyspnea continued for two days until his presentation to the emergency department. On admission physical examination, he had increased work of breathing and decreased breath sounds over the left lung base. Labs were significant for anemia (hemoglobin 8.5 g/dL) and undetectable serial troponins. Initial chest X-ray showed bibasilar opacities. Subsequent computed tomography (CT) chest without contrast showed a soft tissue density within the anterior mediastinum and pericardial cavity as well as a loculated left-sided pleural effusion. A thoracostomy tube was inserted, and pleural studies were consistent with an exudative effusion with over 2.5 million red blood cells but no malignant cells or infectious process. The chest tube output totaled approximately 3 L of bloody fluid over the next 5 days before the output stopped, and the chest tube was able to be removed. CT chest with contrast was then obtained, which showed a 1.5 cm blush of contrast at the level of the SV aorta-rPDA graft that was embedded in the same mediastinal mass seen on prior CT Figures . This suaneurysm ; Video 2 density .Treatment approaches for CABG pseudoaneurysms include open surgical repair, endovascular interventions such as placement of covered stents, or observation . There i


E. coli, C. perfringens and Tyzzerella was higher in LBW feces, but they catch back with the other groups afterwards. HBW puppies showed higher abundances of Faecalibacterium and Bacteroides during the neonatal period, suggesting an earlier maturation of their microbiota. The results of this study suggest that birth weight impact the initial establishment of the gut microbiota in puppies. Innovative strategies would be desired to deal with altered gut microbiota in low birth weight puppies aiming to improve their survival and long term health.Low birth weight puppies present an increased risk of neonatal mortality, morbidity, and some long-term health issues. Yet it has not been investigated if those alterations could be linked to the gut microbiota composition and evolution. 57 puppies were weighed at birth and rectal swabs were performed at 5 time points from birth to 28 days of age. Puppies were grouped into three groups based on their birth weight: low birth weight (LBW), normal birth weight (NBW) and high birth weight (HBW). 16S rRNA gene sequencing was used to highlight differences in the fecal microbiota. During the first three weeks, the relative abundance of facultative anaerobic bacteria such as  One major mortality risk factor identified recently in puppies and studied in many other mammalian species is the birth weight of newborns. Specifically, low birth weight (LBW) puppies have an 8 times higher mortality risk attributed to lower energy reserves, thermoregulation and vitality compared to normal-birth weight (NBW) and high-birth weight (HBW) individuals4. Moreover, this lack of vitality, as evidenced by lower APGAR scores, makes the access to mammary glands for colostrum intake difficult for them, resulting in reduced passive immune transfer, and thus higher risk of infectious diseases5. High mortality in LBW represents important ethical and economic challenges for breeders and veterinarians, making the study of early risk factors a priority to improve the wellbeing of these vulnerable newborns. Besides, deficit of passive immune transfer and metabolic issues, gut microbial composition may impact newborn health.In the canine species, despite progress in veterinary medicine, neonatal mortality remains relatively high with around one out of ten puppies dying during the first three weeks of life7. Many studies suggest that the early development of the gut microbiota may impact the infant’s growth during the first months of life and his health until adulthood8. Thus, altered gut microbiota development can lead to a higher risk of neonatal mortality and diseases, like enterocolitis, and also long-term adverse effects such as the promotion of type-1 diabetes and increased adiposity11. In humans and piglets, numerous studies have demonstrated that gut microbiota of low birth weight newborns differed from the one with normal birth weight13, and that manipulating the gut microbiota could improve outcomes like oxidative stress biomarkers or lipid metabolism15.The gastrointestinal tract (GIT) of mammals harbors trillions of bacteria forming the gut microbiota and playing many different roles in the health of their host, promoting the maturation of the immune system, mucosal integrity, and metabolite productionDespite the importance of the gut microbiota development in general health and even survival of the individual, the relationship between the birth weight and the gut microbiota development during the first weeks of life have never been studied in the canine species.The aim of this study was thus to determine potential differences in the gut microbiota richness and composition depending on birth weight in puppies from birth up to 28 days of age. Our hypothesis was that the fecal microbiota of low birth weight puppies differs in diversity and in composition.p = 0.008 and mean = 8.8 ± 0.8; p = 0.001).Among the 57 puppies studied, 14 were LBW, 29 NBW and 14 HBW. Twenty-three puppies were Australien Shepherd, 17 were Golden Retriever, 12 were Labrador Retriever and 5 were White Swiss Shepherd. Birth weights ranged from 173 to 523 g with a mean value of 399 g ± 82 g  to 53% (D0)  and from 26% (D21) to 36% (D2)  of the total relative abundance . As results were identical, independently of the indices used, only Shannon was kept for graphical visualization. The bacterial richness and evenness significantly decreased from D0 to D2 (p < 0.001), remained stable between D2 and D21 before increasing from D21 up to D28, but still remaining lower than D0  based on the PERMANOVA results using Bray–Curtis distances  , but not HBW (p = 0.29).Among different time points from D0 up to D28, D2 was the only date when a significant difference in bacterial richness (Shannon index) was observed between birth weight quartile groups (01) Fig. . Tukey’sp = 0.006, R2 = 0.08 and p = 0.012, R2 = 0.07; Fig. p adjusted = 0.03), and between LBW and HBW at D21 (p adjusted = 0.04). No differences in the microbial community structure were noticed between quartile groups at D0, D7 or D28.At D2 but also at D21, there was a significant difference in beta diversity (Bray–Curtis index) in the overall bacterial composition depending on quartile groups .At D0, 2 families of strict aerobic bacteria, ies Fig. . No signEnterobacteriaceae (mostly comprised of E. coli), Clostridiaceae (mostly comprised of the Clostridium genus), and Tyzzerella, a genus from the Lachnospiraceae family  . Both Clostridiaceae and Phascolarctobacterium had a VIP score below 1.2, but were kept in the analysis due to their biological interest. The HBW puppies had a significantly higher relative abundance of Faecalibacterium compared to the other two groups (p < 0.001) and a significantly lower relative abundance of Megamonas (p = 0.012). Finally, NBW puppies had a significantly higher relative abundance of Fusobacteriaceae (p = 0.007).As observed in Table 15) Fig. . They alEnterobacteriaceae (mainly E. coli) in LBW puppies compared to NBW (p = 0.043), but the sum VIP of this taxa was below 1.2 .At D7, the linear mixed model highlighted a significantly higher relative abundance of 1.2 Fig. . The CloEnterobacteriaceae (mostly comprised of E. coli) and Lachnospiraceae with a significant difference compared to both NBW (respectively p < 0.001 and p = 0.038) and HBW (respectively p = 0.035 and p = 0.033) . HBW in the other hand had a significantly higher relative abundance of Bacteroidaceae, of which mostly Bacteroides (p = 0.049).At D21, LBW puppies showed a significantly higher abundance of 33) Fig. . Once agMucispirillum and Veillonellaceaeobserved (p = 0.011 and p = 0.04).At D28, , only a few differences were noted in the microbiota composition between the three groups according to puppies’ birthweight Fig. . Those dStacked bar plots per individual for each time points were created to observe the inter-individual variability between puppies. These plots are available in Supplementary file The present study evidenced that gut microbiota varies according to birth weight of puppies. These results suggest that, not only metabolic disturbances, but also intestinal dysbiosis may contribute to the higher neonatal morbidity and mortality of low-birth weight (LBW) puppies. To the authors’ knowledge, this is the first study highlighting such findings.18. Thus, our study added insights on the microbiota development, being the first to give a clear picture of the microbiota development on the first days after birth . Similar results were observed in humans and piglet where the composition of the microbiota shows important shifts in its communities between the first days and the following weeks20.Firstly, significant changes in the gut microbial communities with age were observed in our study. Bacterial richness significantly decreased between D0 and D2 then increased from D2 to D28, with the most significant increase occuring between D21 and D28. Moreover, the important shifts in the microbial composition were noticed mostly during the first days after birth. As one of the main factor shaping the gut microbiota composition and diversity, puppies’ age has already been reported in the literature, but samples were either not collected at birth or during the first week of life (D7)Moraxellaceae, Clostridiaceae, Aerococcaceae, Enterobacteriaceae). The second profile corresponded to a more mature and anaerobic gastrointestinal tract (GIT) with samples from D21 and D28, mainly populated by bacteria such as Bacteroidaceae, Selenomonadaceae and Succinivibrionaceae. The dissimilarity between those two clusters could be drafted by nutritional shifts taking place in puppies during the first weeks of life. In our study, puppies were fed milk exclusively until 14 days of life, whereas older puppies had access to solid food (kibbles). Previous studies demonstrated that the transition from milk to a solid diet is usually followed by an increase in bacterial diversity22. Moreover, dogs fed a high carbohydrate diet (kibbles) present a high Bacteroidetes/Firmicutes ratio24, also observed in our study after D21. An increase of the Bacteroidetes phylum, and particularly Prevotella and Bacteroides genera, as noted in our population on day 21, is known to produce important short-chain fatty acids from carbohydrates and glycans26. Short-chain fatty acids play a major role in the maintenance of gut and immune homeostasis, which could also explain the second cluster at D21.When looking at beta diversity, two main microbial profiles were observed. The first one corresponded to the microbiota profile at a very young age, around the first week of life, when it is highly dynamic and unstable, with the largest inter‐individual composition observed. At that time, environmental conditions are favourable for aerobes and facultative anaerobes  to settle30. As those bacteria and the colonocytes consume oxygen, strict aerobic bacteria are quickly replaced with opportunistic aerobic facultative bacteria which become the dominant taxa on just a few days of age29, as observed in puppies since D2 and until D21 in this study. Those phenomena result in the reduction of the redox potential of the gut, and of better physicochemical conditions for the establishment and growth of obligate anaerobic bacteria. This neocolonization of the gut explains the increase of bacterial richness over time, together with the enrichment of food sources. In our results, Moraxellaceae and Aerococcaceae, two aerobic strict families, represented around 25% of the relative abundance of puppies’ microbiota at birth. At D2, they already almost disappeared, while Enterobacteriaceae alone, mostly comprised of facultative anaerobic bacteria, such as E. coli, represented almost 30% of the relative abundance, inducing the observed decrease in bacterial richness. On later days, the abundance of obligate anaerobes increased, such as Succinivibrionaceae, Bacteroidaceae and Bifidobacteriaceae, while the abundance of facultative aerobes decreased, making our results consistent with the literature in other mammalian species  and of colonocyte metabolism, and in particular the beta-oxydation of fatty acidsies Fig. 30–32.FigAerococcaceae and Moraxellaceae at birth. The lack of those strict aerobic bacteria might have prevented an adequate consumption of oxygen in the GIT during the first days of life. The higher level of oxygen might have induced an earlier and increased colonization of facultative anaerobes, which strived in such an environment compared to the GIT of NBW puppies. The reduced consumption of oxygen also delayed the colonization by strict anaerobes bacteria and subsequently the proper setting of the immune system of newborns34. Indeed, this abnormal dominance of facultative anaerobic bacteria have been widely reported in preterm infants and is known to induce alteration of the intestinal barrier and immunological functions of the host36. Although, it is important to recall this just an assumption; and it would be interesting to monitor different physico-chemical parameters in an in vitro model or to perform metabolomics analyses (including SCFAs) to have a more accurate picture of the situation.Based on this literature, it is possible to develop a hypothesis of what happened between LBW and normal birth weight (NBW) puppies at birth Despite no significant differences, we observed that LBW puppies had lower abundances of Enterobacteriaceae, Clostridiaceae and Lachnospiraceae observed in our study at higher abundance at day 2 and 21 in LBW compared with other groups, are known to be opportunistic bacteria leading to favourable conditions for diseases and specifically inflammatory bowel diseases in the canine species39. Among those families, we found higher abundances of E. coli, Clostridium perfringens and Tyzzerela in LBW puppies. E. coli is demonstrated to be involved in intestinal diseases and systemic infections in newborn puppies40, even though this commensal species remains present in high quantities in healthy puppies compared to adult dogs41. In many animal species, Tyzzerela bacteria are causative agents of Tyzzer’s disease, a usually fatal infectious disease characterized by diarrhea, abdominal distention and hepatic necrotic lesions43, already described in puppies45. As C. perfringens, this species has also been observed in higher abundances in preterm infants and piglets as well, linked to higher risk of necrotizing enterocolitis46.47. This could explain the initial differences of bacterial composition during the first days of life between LBW and NBW. It remains delicate to determine if the composition of the microbiota induces the weakness of the LBW puppies or the opposite, but those results bring new crucial information on the understanding of the higher risk of mortality of LBW puppies48.These findings suggest that LBW puppies develop altered gut microbiota during the first days of life, being most probably associated with their higher risk of death. As observed through their significantly lower APGAR score, LBW puppies are weaker than NBW at birth, making them struggle to reach the mammary glands of their mother and consume colostrumPhascolarctobacterium, a strict anaerobe which uses succinate to produce acetate and propionate. This genus has been associated with energy metabolism regulation in dogs and humans51. A recent study highlighted that LBW puppies were at higher risk of getting overweight once adult52, thus, the lower abundance of Phascolarctobacterium in LBW puppies could be an interesting biomarker to follow. Lower presence of Fusobacteriaceae is also of importance, as those bacteria are reported to be related to a “healthy” canine microbiota when compared to the microbiota of dogs suffering from enterocolitis38. Those bacteria are anaerobes bacteria with a proteolytic activity and are able to produce SCFAs from protein53. Although observed in lower relative abundance, the decrease in Faecalibacterium, a butyrate producing bacteria LBW versus NBW is interesting. Indeed, based on these results, it could speculate that there is a modulation in the development of SCFA-producing bacteria, which fermentation products play a crucial role in colonocytes’ metabolism. Also, this genus is highly O2 and pH sensitive, giving credit to the hypothesis of higher level of oxygen in LBW puppies mentioned previously54.Another relevant genus of interest observed in lower abundances in LBW puppies in the present study was 48.Finally, no differences in the microbiota composition between LBW and NBW puppies was observed at D28. All 57 puppies studied remained healthy during the entire studied period. This suggests that the LBW puppies surviving the neonatal period are strong enough to deal with the delayed microbiota development and are able to catch up with other puppies and harbour a “normal” microbiota after a month. As most neonatal deaths occurred during the first weeks of life, with very-low-birth weight ones being at higher risk of death than NBW ones, further studies are needed to explore the development of gut microbiota in dying versus surviving newborn puppies56.The results of the present study suggest potential preventive strategies to reduce the mortality of LBW puppies. For example, specific pro and prebiotic strains could be given to LBW puppies as soon as possible to stabilize their microbiota and limit potential dysbiosis. Also, avoiding artificial milk and antibiotic as much as possible is highly recommended, as colostrum is a good source of bacteria for the establishment of the microbiota and antibiotic are known to induce dysbiosis, with in particular the proliferation of facultative anaerobic bacteriaFaecalibacterium and Bacteroides respectively. The role of the butyrate-producing Faecalibacterium in gut health has been widely studied recently, to the point it became a bioindicator of inflammatory bowel diseases when its abundance decreases, both in humans and dogs58. Interestingly, this genus seems to be in lower abundance in young puppies compared to adult dogs, so an increase in the abundance of this genus can be linked to the maturity of the puppy41. Another genus observed with higher abundance in HBW puppies in this study, Bacteroides, is shown to be present in lower abundance in preterm infants34. This genus also uses glycans to produce butyrate, reinforces the protection from pathogens in the gut, and as obligate anaerobe, is synonym of the proper maturation of the GIT of the host60. Thus, the higher abundances of Faecalibacterium and Bacteroides in HBW puppies during the neonatal period could suggest the maturation of their microbiota happened earlier than in the other puppies. At birth, the HBW puppies might be able to reach the mammary gland with more ease compared to their brethren, allowing them to get more colostrum and potentially, acquiring a more complete microbiota from it61. At three weeks old, when the first dry diets were presented to puppies, it might be suggested that HBW ingested more food to support the higher needs of their body weight, inducing the increased abundance of Bacteroides linked to dry food consumption23. Those results would suggest that the early maturation of the GIT microbiota of HBW puppies would give them a better protection against sepsis and other gastrointestinal diseases during the first weeks of life62. Since HBW puppies are not specifically studied but usually considered among NBW, it remains difficult to compare those results with literature63. If this hypothesis of an early maturation proved to be true, then fecal microbiota transplantation from HBW puppies to LBW puppies could prove to be another effective strategy to stabilize and improve the microbiota stability of LBW puppies using the more mature one of the HBW.Very few and limited differences between high-birth weight (HBW) and NBW were observed and not recurring from one day to another. The most notable differences were observed at D2 and D21 with higher relative abundances of 64, individual variability of the microbiota composition is a major challenge. On top of it, the LBW studied were in good health and survived the first 2 months of life, meaning their microbiota might not be representative of LBW puppies dying during the neonatal period. All 57 puppies were from the same kennel, which allowed to reduce variability between individuals , but limit the extrapolation to the whole canine species. Also, previous results highlighted that brethren pups have a closer microbiota composition compared to unrelated ones, meaning the litter effect might have an impact on the results65. However, since puppies from a same litter ended up in different quartiles, it allowed to reduce the impact of individual variability of the microbiota composition and confirmed the differences highlighted were most likely a consequence of the birth weight66.Some limits have to be considered when looking at the results of the present study. First, only 57 puppies were involved, of which 14 were considered LBW and 14 were HBW. While this remains higher than similar studies conducted on other species52, this study is the first one to date to describe differences in the fecal microbial populations based on the birth weight of puppies. Further studies, comparing the microbial profile in LWB puppies dying during the first weeks of life with the surviving ones would be desired to identify bacteria responsible for neonatal mortality in the canine species. Another interesting use of these data would be to develop early life microbial biomarkers per birth weight category to predict the risk of diseases later in life, and to propose therapeutical or nutraceutical strategies to orientate the microbial trajectory.Nevertheless, while the impact of LBW on puppies’ health had already been studiedThe animal study was reviewed and approved by the local ethical committee . All applicable guidelines for the care and use of animals were followed. Written informed consent was obtained from the owner of the kennel for the participation of his animals in this study.A total of 57 puppies, born from 11 dams of four different breeds , were recruited within one commercial breeding kennel in France and followed since birth until 2 months of age  and remained with their mothers during the entire experiment with the possibility to suckle freely.68. All puppies were weighed during the first 12 h after birth using a digital scale  and birth weights were recorded. Quartiles of birth weight for the four targeted breeds were determined based on a total of 2719 birth weights registered by the breeder during the last 7 years  was assessed for puppies born during daytime according to Veronessi et al.rs Table . QuartilRectal swabs were performed for all puppies  at birth (D0), 2 (D2), 7 (D7), 21 (D21) and 28 (D28) days after birth. Swabs were then stored at − 20 °C immediately after collection for a maximum of 1 month and then at − 80 °C for the rest of time and until further processing.69 and 806R (GGACTACNVGGGTWTCTAAT)70. PCR amplicons were purified with HighPrep PCR system  and used for library construction with the Illumina NEXTflex PCR-Free DNA sequencing kit . Amplicon libraries were sequenced on an Illumina MiSeq 2500 platform  at GeT-PlaGe INRAE Platform  for paired-end fragment sizes of 250 bp. All reagents used were molecular grade. Four samples gave abnormal results and were removed from the study: one at D0, two at D7 and one at D21.Metagenomic DNA was extracted from rectal swabs using Quick-DNA Fecal/Soil Microbe Miniprep Kit  following the manufacturer’s instructions. Quantification of extracted DNA was checked using a fluorometric method with Quant-iT™ PicoGreen® dsDNA assay kit  measured via QuantStudio™3 Real Time PCR System . The V3–V4 region of the 16S rRNA gene was amplified by PCR using universal primers 341F (CCTACGGGAGGCAGCAG)71, in QIIME 2 (version 2020.2)72. This allowed the identification of amplicon sequence variants (ASVs), under default parameters excluding primers length. ASVs de novo alignment and phylogeny were done respectively with MAFFT and FastTree274. Rarefaction curves were checked for full community sampling depth. Taxonomy was assigned to the resulting 16S rRNA marker genes against Greengenes (gg-13-8-99-nb-classifier)/SILVA (v138) using sklearn classifier method according to Bokulich et al.75. Raw data were rarefied by removing ASVs present in less than 5 samples.A total of 505 raw fastq files were imported, demultiplexed, quality filtered and dereplicated through high resolution sample inference with DADA2p-values below 0.05 considered as statistically significant and box-plot and histogram figures drawn with RStudio (version 2022.02.3 Build 492).All statistical analyses were conducted in R version 4.1.0 , with resulting 76 indices was calculated using the Phyloseq package v1.38.077, and ANOVA coupled to Tukey’s tests were used to evaluate effect of the quartile group on the species richness. Multidimentional scaling (MDS) plots using the phyloseq package were performed to visualize beta diversities between the four quartile groups. To compare the difference in the gut microbiota structure between birth weight quartiles at different time-points, permutational multivariate analysis of variance (PERMANOVA) with 9999 permutations was performed based on Bray–Curtis distances with the Adonis function available in the “vegan” package v2.6–2 of R software. In order to study the differences of bacterial compositions among quartiles, low-abundances reads were first filtered so that ASV present in less than 5 samples were removed. This allowed to carry out sparse Partial Least Squared Discriminant Analysis (sPLSDA) for each bacterial rank at each date using the MixOmics package version 6.22.078. The number of components to keep for the sPLSDA was determined by carrying out predicting receiver operating characteristic (ROC) curves and observing the minimal number of components needed to obtain area under curve (AUC) values higher than 8.0. Variables important to projection (VIPs) were identified using the MixOmics package in R78 to better understand the contribution of the said variable in the bacterial composition variation among quartiles. In parallel, a linear mixed effect model with birth weight quartiles, breed, sex and size of litter  as fixed effects and the mother of the puppies as random effect, was performed to highlight ASV with significant differences between quartiles at each date, using the lme4 package version 1.1–31. Prior to the analysis, the Geometric Bayesian multiplicative (GBM) method was used to transform ASV with a raw abundance of zero into a value based on intra and inter obeservations between samples. All assumptions of linear regressions; linearity and homoscedasticity (scatter plots), independence of the puppies, normality  and lack of collinearity between covariates, were validated prior to the analysis. Newly obtained raw abundances data were then transformed using centered log-ratio transformed to better fit the model, using the “compositions” package80. Analyses were focused on genus and family ranks. In the end, ASVs with both significant differences between quartiles after the linear mixed effect model analysis and a VIP score above 1.2 were considered to describe differences in the bacterial composition81.ANOVA tests were carried out to evaluate differences in APGAR scores among quartile groups, coupled to a Tukey's post-hoc multiple comparison test to elucidate individual differences between groups when needed. Alpha diversity with Observed ASVs, Shannon and InvSimpsonE. coli, Klebsiella and Tyzzerella in LBW puppies, mainly at D2 and D21 after birth as well as a lower bacterial richness at D2. After the third week, no differences were evidenced in the microbiota composition between LBW and NBW puppies, suggesting LBW puppies managed to catch up with their littermates. One possible explanation of this initial difference might be the lack of colostrum intake and physical interactions in LBW puppies with their mother, leading to a weaker bacterial transfer. On the opposite, HBW puppies seem to exhibit an earlier maturation of their microbiota, as shown with higher abundances of Bacteroides and Faecalibacterium on the first weeks of life. Future studies should be considered to further understand the role of the microbiota composition on newborn dogs’ health, such as its impact on metabolic pathways or how the composition differ when comparing healthy puppies to ill ones. Studying the colostrum and maternal microbiotas may also prove to be useful to further understand the setting of the newborn microbiota.The present study is the first to present differences in the fecal microbiota based on the birth weight of puppies. The main findings report a higher abundance in opportunistic bacteria such as Supplementary Information.Supplementary Figure S1.Supplementary Table S1.


Preterm birth remains the leading cause of morbidity and mortality among nonanomalous neonates in the United States. Unfortunately, preterm birth rates remain high despite current medical interventions such as progestogen supplementation and cerclage placement. Case management, which encompasses coordinated care aimed at providing a more comprehensive and supportive environment, is a key component in improving health and reducing costs in other areas of medicine. However, it has not made its way into the general lexicon and practice of obstetrical care. Case management intended for decreasing prematurity or ameliorating its consequences may include specialty clinics, social services, coordination of specialty services such as nutrition counseling, home visits or frequent phone calls by specially trained personnel, and other elements described herein. It is not currently included in nor is it advocated for as a recommended prematurity prevention approach in the American College of Obstetricians and Gynecologists or Society for Maternal-Fetal Medicine guidelines for medically indicated or spontaneous preterm birth prevention. Our review of existing evidence finds consistent reductions or trends toward reductions in preterm birth with case management, particularly among individuals with high a priori risk of preterm birth across systematic reviews, metaanalyses, and randomized controlled studies. These findings suggest that case management has substantial potential to improve the environmental, behavioral, social, and psychological factors with patients at risk of preterm birth. Case management is an underrecognized, potentially important clinical tool in obstetrics. By enhancing patient support and addressing multifactorial prematurity—eassociated risk factors, this approach may improve obstetrical outcomes. Interventions such as progesterone  and cervical cerclage  are indicated for only a small percentage of patients at risk of preterm birth, and they do not guarantee a term delivery.6 Other interventions such as bed rest, omega-3 supplementation, prophylactic tocolytic drugs, progestogen supplementation for arrested preterm labor, home contraction monitoring, and others were initially promising but have since been shown to be ineffective.11It is hard to imagine that Nicholson Eastman, an obstetrician and gynecologist, would have envisioned a world in the 22nd year of the 21st century, where the rate of preterm birth in the United States has not decreased since he made his oft-quoted 1947 statement (>75 years ago), that “only when the factors causing prematurity are clearly understood can any intelligent attempt at prevention be made.”12 Similarly, the Agency for Healthcare Research and Quality defines care coordination as “the deliberate organization of patient care activities between two or more participants to achieve safer and more efficient care.”13 In our review, it was seen that the term “case management” was used more than twice as commonly as care coordination. However, the elements of the programs included considerable overlap and were virtually indistinguishable. Therefore, we shall use the term case management to include care coordination.“Care management” or “care coordination,” among other descriptive monikers, was initially introduced in obstetrics in the mid-1980s as a possible nonpharmacologic approach to improve perinatal outcomes by addressing many of the underlying socioeconomic factors that plague prematurity and other adverse pregnancy outcomes. The Commission for Case Manager Certification defines case management as “a collaborative process that assesses, plans, implements, coordinates, monitors, and evaluates the options and services required to meet the client’s health and human service needs. It is characterized by advocacy, communication, and resource management and promotes quality and cost-effective interventions and outcomes.”17Other fields of medicine, including oncology and cardiology, which, like obstetrics, involve multiple providers, medications, and clinic appointments, regularly employ case management programs. Specifically, within such programs, the use of designated “patient navigators”  and stress reduction programs are proven approaches to improve health outcomes. Research from these fields indicates that incorporation of case managers effectively expands access to health services, improves health outcomes, and increases patient support, particularly among vulnerable populations.18Case management has also shown great promise when incorporated into prematurity prevention programs. Despite this, case management has neither become integrated into the general lexicon for obstetricians nor has it been included as a component of prematurity prevention programs described in previous publications from the American College of Obstetricians and Gynecologists (ACOG) or from the Society for Maternal-Fetal Medicine (SMFM), including the SMFM Preterm Birth Tool Kit.19 This became the foundation for the first example of a program that, although not labeled as case management, incorporated several key elements of later case management programs as follows: identifying pregnancies at high risk of preterm birth, educating patients regarding self-detection of early signs of preterm labor, and providing weekly visits to specialized prematurity clinics.20 In the first year following the implementation of this program, there was a decreased incidence of preterm delivery. Subsequently, a multicenter randomized controlled trial of 5 centers using this system was conducted but found no difference in the rate of delivery earlier than 37 weeks.21The genesis of case management studies addressing the problem of preterm birth likely emanated from original studies by Creasy et al, who developed a risk scoring system for increased risk of preterm birth.27; it is rather to summarize their conclusions and describe the interventions used and various outcomes described in 29 individual studies55 that we also reviewed. To identify additional peer-reviewed studies of case management and preterm birth, we searched the literature for and included all articles with the following terms: case management, care management, care coordination (in association with prematurity), prematurity prevention clinics, prematurity clinics, and prematurity prevention programs. Articles focusing on multiple approaches aimed at prematurity prevention were included. Manuscripts focusing primarily on pharmacologic interventions without specific attention to nonpharmacologic interventions were excluded. We neither found case management studies aimed specifically at multiple gestations nor any reports with a substantial number of multiple gestations included in their analyses. Thus, we limited this discussion to studies focused on singleton gestations.The purpose of this Clinical Opinion is 2-fold: to increase awareness and to review the potential benefits of case management in the prevention of preterm birth. It is not the intent of this document to serve as a systematic review or metaanalysis of this subject, as at least 6 such publications exist currentlyThe elements of case management programs described in the included publications are listed in 56 Other elements that might contribute to the issue of avoidance or earlier detection of preterm delivery include the following: special prenatal clinics with more frequent visits and more specifically trained and focused providers and weekly phone calls and/or home visits. Additional components  increase the likelihood that patients will make it to their clinic visits and take prescribed medications regularly. Furthermore, programs such as smoking cessation and drug counseling address specific behaviors that are known to contribute to preterm birth. Psychology and social service counselors, also involved in a number of programs, have the potential for stress reduction and avoiding or decreasing the severity of other psychological disorders known to have a relationship with preterm birth.57 Given the diversity of the elements included in each program, it was not possible to distinguish which specific element(s) were the most beneficial.In general, case management programs address psychological, environmental, behavioral, and economic factors that are known or are thought to contribute to higher rates of preterm delivery. Programs commonly included a weekly phone call or regular home visits with the patient. However, we observed considerable variation among other program elements. For example, only 11 of the individual programs included smoking cessation programs despite consistent evidence of an association between cigarette smoking and preterm birth; at least 1 study reported a reduction in the rate of preterm birth after introduction of smoke-free legislation.32 or those receiving progesterone supplementation.48 In other cases, however, inclusion was broader and based on age ,47 specific geographic areas of residence,52 race ,35 or insurer . Still others used a telephonic or in-person survey screening tool for risk assessment and often did not define further how pregnancies were classified as high-risk for preterm birth.55In addition to variable program elements, the high-risk inclusion criteria for study enrollment varied among studies. This also likely impacted the ability to discern which individual elements conferred the greatest potential benefit . When coEvaluating whether case management programs are efficacious in preventing preterm birth was difficult owing to the heterogeneity among studies both with regard to program elements  and partOf the publications we reviewed, few involved randomized controlled studies; most were retrospective, observational cohort studies. Further, many studies included populations of patients before and after the intervention, whereas others used control groups that were similar geographically or consisted of patient populations sharing other common factors . However, the populations receiving care varied even within the same health system, and it is likely that unmeasurable confounding factors affected program participation, precluding use of seemingly similar individuals as adequate controls. Outcomes evaluated across studies ranged from prematurity endpoints  to neonatal outcomes  to cost-related outcomes .22 performed a review of randomized trials of specialized prematurity clinics for the Cochrane Database Systematic Reviews. This review was limited to singleton gestations and included 3 studies60 with a total of 3,400 pregnant patients. The authors concluded that these 3 studies contained insufficient data on “prespecified outcomes” and insufficient sample sizes to demonstrate benefit . Randomized studies included in the Cochrane Review are detailed as follows. In 1989, Main et al58 randomized 943 inner-city pregnant individuals at high risk of preterm birth to a program that included frequent prenatal visits and cervical exams, education regarding signs and symptoms of preterm labor, and a 24-hour hotline to ensure easy access to obstetrical care. The authors found no difference in prematurity-related outcomes among the higher-risk patients included (preterm birth incidence of 23.2% in the intervention arm vs 20.7% in the control arm). They speculated that the program’s lack of impact on prematurity may have resulted in part from reduced program adherence among subjects in the study population. In 1989, Iams and Johnson59 presented results from their randomized trial of 370 pregnant patients, wherein those who were randomized to the study group, as in the analysis by Main et al, received care in a specialized clinic with frequent cervical exams. They also received specific preterm labor symptom education. In contrast to Main et al, Iams and Johnson found that more patients randomized to the study group received tocolysis and subsequently delivered at term than did those who received standard care. The Whitworth et al analysis reported the preterm birth rate in the Iams et al study to be 13.2% (24/182) in the study group and 18.6% (35/188) in the control group . Hobel et al60 in 1994 published results of a randomized controlled trial of 1774 patients participating in specialized clinics, which included special education and increased frequency of prenatal visits. This study found a 19% reduction in the preterm birth rate; this did not reach statistical significance, but “when risk factors for preterm birth were taken into account,” the finding was statistically significant . The Cochrane Review concluded that there was no clear evidence of benefit in terms of reduction in preterm birth rates with case management among these 3 studies. However, this was a small and early metaanalysis in the evolution of case management study evaluation, and the point estimate lay in the direction of benefit without the power to test for significance.In 2011, Whitworth et al29 randomized 173 high-risk pregnant patients with well-described, common risk factors for preterm delivery. The control group received usual prenatal care for high-risk patients at an academic medical center, and the study group received home visits by trained nurses on alternate weeks in addition to the usual prenatal care for high-risk patients. Each trained nurse visit included psychological and nutritional counseling, referral to community resources, education of signs and symptoms of preterm labor, monitoring of clinic visits, and medication compliance and home environment assessment. Individuals randomized to the nurse home visit intervention group were less likely to be admitted for threatened preterm labor and had a lower rate of delivery before 37 weeks’ gestation . Based on our calculations using the data provided, this reduction did not achieve statistical significance (P=.15). However, a significant reduction in perinatal mortality was noted for those randomized to the intervention arm vs the control arm . The nurse home visit intervention group was also associated with overall savings of $2.8 million even when the costs of the visits were considered.We identified only 1 other randomized controlled trial not included in the Cochrane Review. In 2001, Brooten et al25 concluded that the results of individual trials varied, with overall fewer than half showing benefit or “promise”; the fourth26 concluded that there was ample evidence to suggest integration of case management into prematurity prevention strategies. The metaanalysis, conducted by Fernandez Turienzo in 2015,27 included 15 trials involving 22,347 pregnancies and concluded that individuals receiving “alternate care models” were less likely to experience preterm birth . Most of the systematic reviews and the metaanalysis reported challenges such as those we observed with study comparisons, again given the wide variation in program methodology, including referral criteria or criteria for inclusion, interventions offered, and outcomes compared.Among the 4 other systematic reviews and 1 metaanalysis identified, there were mixed conclusions. Three systematic reviewsThus, it is difficult to conclude definitive benefit of case management programs for prematurity prevention, primarily, we feel, because of the heterogeneity of the various programs, populations included, and outcomes selected. However, the combination of suggestive trends in the metaanalysis data and randomized trials (2 of 4 showing some benefit) suggest that case management programs have the potential to reduce preterm delivery, its consequences, and/or associated costs. It is important to note that several of the aforementioned “negative” studies are decades old. The programs described in these studies did not include elements of more comprehensive case management programs that were developed and described later; this point also was made in the Cochrane review. In addition, new interventions for specific risk factors such as short cervix on endovaginal ultrasound or previous preterm birth were not incorporated into the prematurity clinic algorithm; only a few of the more recent studies included patients on progesterone, and none included patients on low-dosage aspirin.62 Existing pharmacologic interventions are limited. The known benefit of progesterone for prematurity prevention is restricted to patients with previous preterm birth and those with ultrasound-identified short cervix, both of which taken together affect only a small minority of patients who ultimately deliver prematurely. One of the few practices that might have influenced the recent reduction in the rate of prematurity involved policies and campaigns championed by national organizations  to avoid elective delivery before 39 weeks’ gestation and the reduction of twin pregnancies through single-embryo transfers for individuals conceiving via in vitro fertilization and other artificial reproductive technologies.63 Recent attention has been paid to the contributions of patient stress, social support, and socioeconomic factors in the development of preterm birth and other adverse pregnancy outcomes.Several arguments support more wide-spread implementation of case management programs or specialty clinics for prematurity prevention. The rates of preterm birth continue to rise, though modestly, in a disturbing trend, and overall rates remain unacceptably high— approximately 10.1% after peaking at 12.8% in 2006.34 Cost effectiveness can be maximized by proper patient selection, as efficacy— and therefore cost savings—appears greatest in those with the highest a priori risk of preterm birth. As described above, case management programs have become commonplace in fields of medicine outside of obstetrics that require comprehensive patient care. Further, most large health insurance plans have implemented and provide coverage for such programs in these fields.64 Insurers have concluded that major cost savings can be achieved. More specifically, as it potentially relates to patients at high risk of preterm delivery, 83% of insurers use case management focused on their highest-cost patients.64Studies evaluating the cost effectiveness of case management have concluded that if improved outcomes are shown, programs are also cost-effective.67 may have the potential to improve outcomes in case management programs and enhance cost efficiency. Of the 29 original papers reviewed, 20 provided information regarding whether outcomes in the case management program were improved if the population was risk-stratified vs evaluation across the overall population. All but 153 of the 17 reports that included risk-stratified patients55 who were at a higher risk of preterm birth demonstrated reduced rates of preterm birth, low birthweight, and/or NICU admissions with case management. In addition, 2 reports that evaluated cost found overall reduced costs with case management.34 In contrast, in the 3 studies that included only patients with Medicaid or those with lower socioeconomic status but no other risk stratification, there was no reduction in preterm birth or low birthweight.49 These findings emphasize the importance of risk stratifying on multiple factors, including medical and socioeconomic factors but not socioeconomic factors alone.Previous case management programs reporting on older cohorts used variable ways to define those at “high-risk” of preterm birth. Together, these data have demonstrated that there not only is a need to use all “medical” tools available to address the critical problem of prematurity but there is also the possibility that now, more than ever, specialized prenatal care programs may provide critically needed social and emotional support to patients at the highest risk of preterm birth. In addition, case management programs are low-risk, as they do not involve costly, experimental, or understudied drug therapies.Because case management is low-risk and has the potential to reduce prematurity-related costs, it is reasonable to consider implementation of comprehensive programs—or some of their elements if limited resources are available—with the evidence presented here. However, as we have outlined, the current data are imperfect, and additional, high-quality evidence likely will be necessary before case management will be adopted widely as a recommended strategy for prematurity prevention. Unfortunately, there currently exists no optimal study design, as considerable variability appears in the selection of patients for inclusion and the interventions included in case management programs. Owing to the heterogeneity of preterm birth and its underlying etiologies, it is unlikely that a “one-size-fits-all” approach will be the most effective. Hence, our proposed program, as outlined in the Case management is a low-risk and underrecognized yet potentially beneficial element that can reasonably be considered as a component of prematurity prevention strategies in the United States. Tracking contemporaneous outcomes from ongoing prematurity prevention centers, especially those with broadly inclusive case management programs, should be considered. Further, evaluation of individual program elements from these centers will enable refinement of the optimal formula for case management program implementation at other institutions. In addition, multidisciplinary partnerships supported by grant funding, statistical support, and other means may help facilitate these analyses, including determination of cost efficacy.


Abnormal microbial colonization in the gut at an early stage of life affects growth, development, and health, resulting in short- and long-term adverse effects. Microbial colonization patterns of preterm infants differ from those of full-term infants in that preterm babies and their mothers have more complicated prenatal and postnatal medical conditions. Maternal complications, antibiotic exposure, delivery mode, feeding type, and the use of probiotics may significantly shape the gut microbiota of preterm infants at an early stage of life; however, these influences subside with age. Although some factors and processes are difficult to intervene in or avoid, understanding the potential factors and determinants will help in developing timely strategies for a healthy gut microbiota in preterm infants. This review discusses potential determinants of gut microbial colonization in preterm infants and their underlying mechanisms. According to the World Health Organization (WHO), preterm infants (PTIs) are those born at < 37 weeks of gestation. Every year, 15 million PTIs are delivered worldwide, which accounts for more than 10% of all deliveries (Harrison and Goldenberg The gut microbiota (GM), which includes trillions of microorganisms inhabiting the digestive system, is complex and dynamic Brody . StartinGM colonization starts from, if not earlier than, the initiation of labor. The early period after birth plays a vital role in the establishment of the GM. Patterns of microbial colonization in PTIs differ from those in full-term infants (FTIs) owing to prenatal factors, birth mode, feeding type, and antibiotic use are weaned  than that of non-exposed PTIs, irrespective of postnatal antibiotics  or preeclampsia, exhibited a different GM from that of healthy controls , and demonstrated the cross-generational transfer of donor fecal bacteria to her late-born infant. Intervention with the maternal GM before labor may be a novel strategy for modulating the infant GM, especially when the mother is experiencing gut dysbiosis.The maternal GM is relevant to immune development in infants, neurodevelopment in children, and the development of asthma  from the environment , 294,657 (21.9%) were exposed to prenatal antibiotics  are frequently administered during emergency C-section. This may result in a decrease in the alpha diversity and abundance of Comamonadaceae, Staphylococcaceae, and unclassified bacilli, as well as a lower relative abundance (P < 0.05) of Enterobacteriaceae were observed in PTIs from IAP-exposed mothers than in those from non-IAP-exposed mothers. Most of these differences, however, disappeared at 90 days of age  are not dominant in the preterm gut  and Bifidobacterium  are the most frequently used probiotic bacteria in humans to manage dysbiosis, followed by Streptococcus, Enterococcus, Lactococcus, Pediococcus, Bacillus, Escherichia, and certain Saccharomyces yeast strains   or left untreated as controls (n = 10). No significant difference was observed in alpha diversity between gorups  were either administered B. lactis), or non-probiotic formula   than that of the BM (19.57%) and PF (9.57%) groups. Bifidobacterium was gradually enriched in all infants, with a larger proportion in the PF group than in the other two groups. The GM values of the three groups tended to be similar by week 12. Therefore, probiotic supplementation may affect GM colonization and reduce the number of some potential pathogens.In a previous cohort study by Chi et al. , 138 PTIB. infantis EVC001 reduced enteric inflammation. A higher abundance of Bifidobacteriaceae, with rapid development and significantly lower levels of key pro-inflammatory biomarkers, were detected in the B. longum subsp. infantis EVC001-treated group (n = 31) than in the control group (n = 46). Furthermore, B. longum subsp. Infantis EVC001 improved the functional capacity of the GM of PTIs for HMO utilization. In the ProPrems trial of very premature infants (n = 1099), supplementation with B. longum subsp. infantis BB-02, Streptococcus thermophilus TH-4, and B. animalis subsp. lactis BB-12 was associated with an increased abundance of Bifidobacterium soon after birth, resulting in a reduced NEC risk  who received Bifidobacterium (15.1%) and Lactobacillus (4.2%) abundances were observed in groups supplemented with L. acidophilus NCIMB701748 and B. bifidum ATCC15696 than observed in the control group (Bifidobacterium 4.0% and Lactobacillus 0%). Bifidobacterium abundance remained high after hospital discharge, suggesting successful long-term colonization, whereas that of Lactobacillus was reduced (Abdulkadir et al. L. acidophilus and B. longum subsp. infantis had a higher relative abundance of Bifidobacterium and Lactobacillus than that of FTI controls. The FTIs had a higher abundance of Streptococcus, Veillonella, and Haemophilus. At 4 weeks and 4 months, the overall microbial diversity and resistome of the probiotic-supplemented infants were similar to those of the more mature infants. This indicates that probiotics may induce colonization resistance and alleviate the harmful effects of antibiotics on the GM and antibiotic resistome (Esaiassen et al. Greater Initiating probiotics shortly after birth has been recommended in several studies because of its benefits to the GM (Plummer et al. The GM is strongly associated with the health status of PTIs. Although it is generally believed that GM colonization begins as the neonate leaves its mother, prenatal maternal status can pre-dispose the infant to dysbiosis before delivery. PTIs born via C-section or vaginally are initially colonized by different microbiota and exhibit different microbial distributions. Breastfed PTIs, or those supplemented with HMOs, may exhibit a more “normal” GM resembling that of FTIs. Antibiotic and probiotic administration may significantly influence the GM composition. The influence of all of the aforementioned factors subsides with age.


The progression of global warming and increase in instances of extreme weather have received considerable attention. We conducted a cohort study on women of childbearing age in Yunnan Province, examined the association between ambient temperature and humidity on preterm birth and evaluated the effects of extreme weather during early pregnancy and before parturition on preterm birth.We conducted a population-based cohort study on women of childbearing age 18–49 years who participated in National Free Preconception Health Examination Project (NFPHEP) in Yunnan Province from January 1, 2010, to December 31, 2018. Meteorological data, namely daily average temperature (°C) and daily average relative humidity (%), were obtained from China National Meteorological Information Center. Four exposure windows were explored: 1 week of pregnancy, 4 weeks of pregnancy, 4 weeks before delivery, and 1 week before delivery. We used a Cox proportional hazards model and adjusted the potential risk factors for preterm birth to obtain the effects of exposure to temperature and humidity on preterm birth among the stages of pregnancy.At 1 week of pregnancy and at 4 weeks of pregnancy, the association between temperature and preterm birth was U-shaped. The correlation between relative humidity and the risk of preterm birth was n-type at 1 week of pregnancy. The correlation between preterm birth and temperature and relative humidity at 4 weeks before delivery and at 1 week before delivery is J-shaped. Low temperature and low humidity were protective factors against preterm birth, whereas high temperature and high humidity were risk factors for preterm birth.The effects of high temperature and extremely high temperature were the strongest at 4 weeks before delivery, with HRs of 1.417 (95% CI: 1.362–1.474) and 1.627 (95% CI: 1.537–1.722), respectively. The effects of extremely low humidity and low humidity were strongest at 1 week before delivery, with HRs of 0.681 (95% CI: 0.609–0.761) and 0.696 (95% CI: 0.627–0.771), respectively.Temperature and relative humidity affect preterm birth differently for each pregnancy stage. The effects of meteorological factors on pregnancy outcomes such as premature birth should not be ignored. SeasonaGlobally, preterm birth complications are the second leading cause of death among children under 5 years of age, after pneumonia . ApproxiChina possesses a large territory comprising a variety of natural environments. Therefore, the association between premature birth and temperature and humidity may differ by region. Most national studies have analyzed meteorological factors by province, and the results have been inaccurate because of the high granularity. Our study focused on Yunnan Province, China, which includes 16 cities , and we analyzed the basic characteristics of temperature and humidity by city. The low granularity ensured that the association between preterm birth and temperature and humidity was accurate.Yunnan is at a subtropical northern latitude and has a climate typical of such a region. The average annual temperature is above 15°C, and the average annual precipitation is 750–1750 mm. Precipitation is unevenly distributed throughout the year, with distinct dry and rainy seasons. In addition, Yunnan has the most ethnic groups in China but is less economically developed than the rest of the country; the province exhibits regional economic disparity, and medical and health resources are also unevenly distributed. Therefore, targeted assistance and interventions must be implemented to improve its health services and poverty relief initiatives .Studies have indicated that high temperatures were associated with a high risk of preterm birth , 12. How2.We conducted a population-based cohort study on women who attempted to become pregnant and participated in the National Free Preconception Health Examination Project (NFPHEP) from January 1, 2010, to December 31, 2018, in 16 cities in Yunnan Province. The NFPHEP was launched by the Chinese National Health and Family Planning Commission in 2010 to provide free health examinations and other services before conception for couples who plan to become pregnant within 6 months as well as follow-up during the first trimester of pregnancy and after delivery. This study was approved by the Institutional Review Board of the Chinese Association of Maternal and Child Health Studies (AMCHS-2014-6). All participants provided written informed consent before enrollment .Trained and qualified local health workers used a standardized questionnaire to collect baseline information from the women who participated in the NFPHEP, namely age, education level, history of childbirth, and adverse pregnancy outcomes. The health workers measured the participants’ height, weight, and concentration of hemoglobin and calculated their body mass index (BMI). For the diagnostic criteria for anemia, this study referenced the diagnostic threshold recommended by the World Health Organization [lower than 120 g/L for nonpregnant women ]. Matern2.1.Gestational age was the first day of the last menstruation until the end of the process, approximately 280 days (40 weeks). The primary outcome was preterm birth, which was defined as a delivery from 28 weeks to less than 37 weeks of gestation . The pre2.2.Meteorological data from 16 cities in Yunnan Province, namely daily average temperature (°C) and daily average relative humidity (%) between 2010 to 2018, were obtained from China National Meteorological Information Center. Because the etiological threshold for the effects of temperature and relative humidity exposure on risk of preterm birth is unclear, several exposure windows were explored.The windows of exposure were 1 week of pregnancy, 4 weeks of pregnancy, 4 weeks before delivery, and 1 week before delivery. Term births were censored at the end of the 36th week of gestation because the risk of preterm birth was eliminated . For fulThe daily exposure temperature and relative humidity were matched to each pregnant woman according to the date of conception, and the average exposure in each window was calculated to identify the association between premature delivery and temperature and humidity. Extremely low temperature and humidity were the first percentile of temperature and humidity distribution. Low temperature and humidity were the fifth percentile of the temperature and humidity distribution. High temperature and humidity were the 95th percentile of the temperature and humidity distribution. Extremely high temperature and humidity were the 99th percentile of the temperature and humidity distribution .2.3.2), anemia (yes or no), habit of smoking during pregnancy (yes or no), habit of drinking alcohol during pregnancy (yes or no), and fetal sex , were adjusted.Covariates related to preterm birth, namely age , education , history of delivery (yes or no), history of adverse pregnancy outcomes (yes or no), BMI  to create a nonlinear relationship with preterm birth and then incorporated the basis function into the Cox proportional hazards model to form the basic model . We thenGA is the time variable, gestational age, PTB is whether the child was born prematurely, cb represents the basis function, MMi represents the average value of the meteorological variables in the ith window of exposure, df is the degree of freedom, β is a coefficient, MAG is the age of the mother, CL is the maternal education level, PD is the history of delivery, AP is the history of adverse pregnancy outcomes, BMI is the body mass index, AN is anemia, AL is a habit of smoking during pregnancy, SK is a habit of drinking during pregnancy, and GD is the fetal sex.where Based on the results of the Cox model, we plotted the risk exposure–response curves for temperature and relative humidity during pregnancy with respect to preterm birth to represent the temperature and relative humidity distribution. In addition, we calculated specific hazard ratios (HRs) and 95% confidence intervals (CIs) relative to the median temperature for extreme temperature and humidity. All statistical analyzes were performed using R (version 4.0.2). The “survival” and “smoothHR” packages were used to create a Cox proportional risk regression model with a significance level of 0.05 on both sides.3.This study recruited 214,695 participants, of whom 2,684 had missing delivery time or address data, 6 were younger than 13 years of age or older than 50 years of age, 1,132 had multiple births, 589 had stillbirths, 3,329 had a gestational age of less than 20 weeks or more than 44 weeks, and 1,184 had an abortion or induced labor—these participants were excluded, and 205,771 participants remained . Supplem3.1.The lowest mean temperature was observed in Diqing Tibetan Autonomous Prefecture (5.87–6.98°C), and the highest was observed in Xishuangbanna Dai Autonomous Prefecture (21.6–22.3°C). The lowest average relative humidity was observed in Lijiang (58.8–61.6%), and the highest was observed in Xishuangbanna Dai Autonomous Prefecture (82.4–83.1%). Of the 205,771 participants, 18,014 had preterm births, accounting for 8.75% of the participants. Qujing had the lowest preterm birth rate: 4.63%. Diqing Tibetan Autonomous Prefecture had the highest preterm birth rate: 19.08% .3.2.p < 0.05).3.3.4.4.1.Our study found that an increased risk of preterm birth was significantly associated with high temperatures during pregnancy. Temperature during the early stage of pregnancy (1 and 4 weeks of pregnancy) was found to be associated with preterm birth in a U-shaped curve. The association between temperature and preterm birth was J-shaped during the preterm period (1 and 4 weeks before delivery). High temperatures (P95) and extremely high temperatures (P99) were both risk factors for preterm labor during all four exposure windows. Extremely low temperatures (P1) and low temperatures (P5) at 1 and 4 weeks of pregnancy were both risk factors for preterm birth and that extremely low temperatures (P1) and low temperatures (P5) at 1 and 4 weeks before delivery were protective factors for preterm birth. Low humidity was a protective factor for preterm birth, whereas high humidity was a risk factor for preterm birth. The correlation between relative humidity and risk of preterm birth was n-type at 1 week of pregnancy and the correlation between relative humidity and preterm birth at 1 and 4 weeks before delivery was J-shaped.4.2.Our study has several advantages. First, our study is the first study to explore the effects of both temperature and relative humidity during the early stage of pregnancy and before parturition on preterm birth in women of childbearing age. Second, our study is a long-term, population-based, large-sample cohort study on all women of childbearing age who participated in the NFPHEP and gave birth in Yunnan Province, resulting in high representativeness. In addition, we considered the effect of extreme weather, namely high temperatures, high humidity, low temperatures, and low humidity, on preterm birth to accurately describe the effects of meteorological factors on preterm birth.Our study also has some limitations. The NFPHEP does not collect information regarding pregnancy complications such as gestational hypertension, gestational diabetes, and other factors affecting preterm birth (such as infection); this may have affected the results to a certain extent. Numerous studies have reported that air pollution is associated with premature birth, but we did not collect data on air pollution in Yunnan Province from 2010 to 2018. Subsequent studies should investigate air pollution and preventative measures in their analyzes.4.3.Preterm birth is a global public health. The increases in global warming and extreme weather have received much attention in recent years, and many studies have been conducted on preterm birth that may be related to environmental factors. From a biological perspective, the early stage of pregnancy, specifically the weeks around conception when gametes mature, fertilization occurs, and the developing embryo forms, is a critical period . This stNumerous studies have investigated the effect of temperature on preterm birth. An Australian study using Cox proportional hazards models and discovered that between July 1994 and December 2013, the relationship between temperature  and risk of preterm birth formed a U-shaped curve. The HRs of preterm birth increased with temperature during the first two trimesters but nonsignificantly . A 2019 Few studies have investigated the effect of humidity on preterm birth. A Romanian study with a small sample analyzed the effects of atmospheric conditions on premature birth and discovered no significant correlation between humidity and preterm birth . A studyExtreme weather has been documented to cause numerous health problems , 29, 30.The exact mechanisms by which ambient temperatures cause preterm birth is unclear, but studies have proposed several hypotheses. First, dehydration and reduced blood flow caused by exposure to high temperatures may cause uterine contraction , 32. Sec5.This study demonstrated that temperature and relative humidity during pregnancy were nonlinearly associated with risk of preterm birth. Temperature and relative humidity affect preterm birth differently for each pregnancy stage. High and low temperatures increase the risk of preterm birth during the early stage of pregnancy. High temperatures and high humidity increase the risk of preterm birth during the late stage of pregnancy. The meteorological factors on pregnancy outcomes such as premature birth should not be ignored.The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.The studies involving human participants were reviewed and approved by Institutional Review Board of the Chinese Association of Maternal and Child Health Studies (AMCHS-2014-6). The patients/participants provided their written informed consent to participate in this study.YW: writing–original draft, methodology, software, and data curation. JY: writing–original draft, methodology, and software. YY and CK: data curation and investigation. WJ and JL: writing–review and editing, supervision, and methodology. HY: data curation, investigation, project administration, and supervision. ML: conceptualization, funding acquisition, project administration, and supervision. All authors contributed to the article and approved the submitted version.This study was supported by the grant from National Natural Science Foundation of China (No. 71874003).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.The handling editor LP declared a shared affiliation with the authors at the time of review.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.