Effect Of Gestational Weeks Of Delivery On Perinatal Outcomes In Low-risk Singletons At Term-A Retrospective Case Cohort Study

BackgroundTerm pregnancy refers to the pregnancy of a pregnant woman between 37⁺⁰weeks and 41⁺⁶weeks,during which the person who gives birth is called term birth.Previous studies have shown that the maternal and infant outcomes of different weeks of delivery during term pregnancy are consistent and good compared with premature delivery and late delivery.However,more and more studies have found that the incidence of maternal and neonatal adverse outcomes is not the same at different gestational weeks during term pregnancy.To further study the effect of weeks of delivery on maternal and infant outcomes,the American College of Obstetricians recommends that term be classified into early term(37⁺⁰weeks to 38⁺⁶weeks),term(39⁺⁰weeks to 40⁺⁶weeks),and late term(41⁺⁰weeks to 41⁺⁶weeks).Some studies suggest that the incidence of severe complications（especially respiratory diseases）and death in early term delivery is similar to that of late preterm delivery(34⁺⁰weeks to 36⁺⁶weeks),and that perinatal outcomes at 37and 38 weeks are not the same.At late term delivery,not only the complications and mortality rate of the newborn,but also the obstetrical complications such as vaginal operation midwifery rate,endometritis,injury of the birth canal,prolonged labor course and caesarean section rate all increased with the prolongation of gestational weeks,which seriously affected the prognosis of the mother and infant.Some studies have analyzed the perinatal outcomes of mothers and infants in different weeks of delivery.The results show that the distribution of incidence rate and mortality rate and the odds ratio of mothers and mothers is U,and the lowest point is 39⁺⁰⁶weeks.The author suggests that the risk of maternal and infant complications is lower in this period,but there are some who doubt the rule because of the inconsistency of the results.These studies often lack a distinction between low-risk and high-risk pregnancies,and do not compare in detail whether the effects of each gestational week after term on pregnancy outcomes are different,leaving the independent impact of the gestational weeks on low-risk single pregnancies unclear.In recent years,there are often some undefined medical indications in clinical work,but due to various medical needs or individual requests for planned delivery of low-risk full-term pregnancy cases,unindicated planned delivery gradually increases.Therefore,it is necessary to further study whether there is a"optimal gestational week"to minimize the combined risk of maternal and infant complications and to guide clinical decision making of planned delivery for low-risk pregnant population.ObjectiveThrough collecting the clinical data of perinatal period of full-term mothers and infants,a retrospective study was conducted to explore the occurrence of adverse outcomes of mothers and infants in different gestational weeks,and to analyze the relationship between gestational weeks and maternal and infant adverse outcomes,so as to provide clinical basis for answering"the best gestational week for delivery"and guide clinicians to make decisions.MethodA retrospective study was conducted to select 500 pregnant and lying-in women who delivered at term in the Henan Provincial People’s Hospital from 2018 to 2021.According to the gestational week at delivery,there were 77 cases in 37⁺⁰⁶weeks group,113 cases in 38⁺⁰⁶weeks group,129 cases in 39⁺⁰⁶weeks group,112 cases in 40⁺⁰⁶weeks group and 69 cases in 41⁺⁰⁶week group.Obstetric medical records were used to record the basic situation of pregnant women and birth information of newborns,including age,number of pregnancies,weight gain during pregnancy,delivery mode,weight of newborn and hospitalization days of pregnant women.The incidence of perinatal death,hospital stay≥5,meconium stained amniotic fluid,macrosomia,Apgar score<7 at 5 min,neonatal admission rate in NICU,dystocia,conversion to operation due to abnormal fetal heart rate or abnormal fetal position during trial delivery,postpartum hemorrhage were recorded and compared with delivery at 39⁺⁰⁶weeks.SPSS22.0 software was used for statistical processing.Normality test（Shapiro-Wilk test,α=0.10）was first performed for quantitative data,’?X±S for quantitative data conforming to normal distribution,and one-way ANOVA was used for comparison among groups;data not conforming to normal distribution was described with number[interquartile range（IQR）],and multiple sample rank sum test was adopted for comparison;categorical data was described as n（%）and compared with c2 test;if theoretical frequency was too small,Fisher exact probability method was adopted;P<0.05 was regarded as statistically significant difference.In comparison between groups,independent sample t-test was used for quantitative data conforming to normal distribution;non-parametric Wilcoxon test was used for quantitative data not conforming to normal distribution,with P<0.0125 as statistical significance;odds ratio of perinatal complications was calculated by binary logistic regression analysis with reference to delivery group of 39+0～6 weeks.Confounding factors commonly seen in the literature（age,parity,parity,weight gain during pregnancy）were selected as potential covariate adjustment factors.Results1.General information:There were significant differences in age,hospitalization days and neonatal weight among groups（P<0.05）.There was no significant difference in weight gain during pregnancy（P>0.05）.With the prolongation of gestational weeks,age decreased gradually and neonatal weight increased gradually.The median hospitalization days in 37⁺⁰⁶weeks group were 6 days,significantly higher than those in other groups.Compared with 39⁺⁰⁶weeks,the hospitalization days of early term group were significantly longer,the birth weight of newborn was lower,and the weight of late term group was higher（P<0.0125）.There was no significant difference in age between groups and 39⁺⁰⁶weeks.2.Complications:There were significant differences among the five groups in pregnancy>1,delivery>1,cesarean section,amniotic fluid staining,macrosomia,low Apgar score,conversion to NICU,hospitalization days≥5 days,labor dystocia,conversion to surgery and postpartum hemorrhage（P<0.05）.Compared with 39+0～6 weeks,there was no significant difference in the incidence of postpartum hemorrhage,lower neonatal score and postpartum hemorrhage among the groups（P>0.0125）.Cesarean section accounted for 70.1%and 370.8%in early term group,and 44.2%at 39 weeks,respectively（P<0.0125）.The fecal staining rate of amniotic fluid in early term group was 3.9%and 8.0%,respectively,which was lower than that at 39 weeks（20.2%）,while that at 41 weeks was 49.3%,higher than that at 39weeks P<0.0125.The NICU conversion rate of macrosomia,neonate and transoperative operation rate were 7.8%,9.3%,3.9%at 39 weeks and 20.3%,26.1%,15.9%at 41 weeks respectively,the difference was significant（P<0.0125）.The length of hospitalization was 74%,72.6%,and 53.5%at 39 weeks,respectively（P<0.0125）.The incidence of dystocia at 38 weeks was 3.5%,lower than 39 weeks（14.7%）,the difference was significant（P<0.0125）.3.Multivariate regression analysis showed that compared with 39⁺⁰⁶weeks delivery,the risk of meconium-stained amniotic fluid（OR=3.997,95%CI:2.087-7.654）,macrosomia（OR=3.61,95%CI:1.145～9.014）,low Apgar score（OR=5.867 95%CI:1.471-23.404）,neonatal transfer to NICU（OR=3.411,95%CI:1.517-7.669）,and trial transfer to surgery（OR=4.189,95%CI:1.378-12.734）were significantly increased in early term group（OR=2.953,2.231）.After the gestational week of delivery exceeded 39 weeks,the risk of meconium-stained amniotic fluid and transfer to surgery increased with the prolongation of gestational week（Ps<0.05）.Conclusions1.Early term delivery increases the probability of cesarean section and the hospitalization days of pregnant women.2.Over 39 weeks,the risk of macrosomia,meconium staining of amniotic fluid,low Apgar score,neonatal transfer to NICU,dystocia,etc.increased with prolonged gestational age,and the probability of postpartum hemorrhage also increased.3.The best time to terminate pregnancy is between 39 and 40 weeks in a population of low-risk singletons without comorbidities.