Association Of Maternal Gestational Weight With Birth Outcomes And Infants' Physical Development:A Population Based Cohort Study

Objective:Maternal gestational weight,an important indicator to evaluate the fetal intrauterine nutrition status,is the accumulation of pre-pregnancy weight and gestational weight gain.Previous studies have demonstrated that maternal pre-pregnancy BMI and gestational weight gain are closely related to fetal health,and may influence the birth outcomes and infants' health status after birth.However,there is lack of evidence from large scale population based cohort study.Besides,there is no optimal recommendation of gestational weight gain for Chinese women at present.Therefore,the main purposes of this study were follows:1.This population based cohort study was designed to investigate the associations between pre-pregnancy BMI,gestational weight gain(GWG)/BMI gain with neonatal birth weight and Apgar score,and to explore the independent as well as joint associations of pre-pregnancy BMI,GWG/BMI gain with 7 birth outcomes:SGA,LGA,LBW,macrosomia,PTB,birth asphyxia and cesarean section.2.To investigate the influence of maternal pre-pregnancy BMI,GWG/BMI gain on offspring's physical development and risk of overweight/obese during 0-2years.3.To explore the optimal recommendation of pre-pregnancy BMI and gestational weight gain(GWG)/BMI gain for the Chinese women,thus to provide evidence for pre-pregnancy and prenatal health care improvement.Methods:1.Part One:Based on the Maternal and Children Healthcare Information Tracking System of Wuhan,84,079 women who lived in the urban areas of Wuhan and delivered during June,2011 and June,2013 were selected in our study.Pre-pregnancy BMI was categorized into four groups:underweight(<18.5 kg/m2),normal weight(18.5-23.9 kg/m2),overweight(24-27.9 kg/m2),and obese(?28 kg/m2).GWG was categorized as below,within and above the recommendations,according to the recommendations of the Institute of Medicine(IOM)(2009).Gestational BMI gain was then divided into three groups:<5 kg/m2,5-10 kg/m2 and ?10 kg/m.Analysis of variance,Pearson correlation analysis,unconditional logistic regression and Wald test,etc.were used to analyze the impact of pre-pregnancy BMI,GWG/BMI gain to the neonatal birth weight,Ponderal Index(PI)and Apgar score,as well as the associations of pre-pregnancy BMI,GWG/BMI gain with the risk of LBW,macrosomia,SGA,LGA,PTB,birth asphyxia and cesarean section.The associations of GWG/BMI gain with different birth outcomes were also evaluated by stratifying pre-pregnancy BMI.2.Part Two:Infants from the cohort of Part One were followed up at 1 month,6 months,12 months and 24 months,their height,weight and head circumference were measured respectively,and the feeding patterns were recorded.According to 2006 WHO standard,WAZ,LAZ,BAZ and HCZ were calculated and the nutrition status was evaluated.Utilizing Pearson correlation analysis,generalized linear regression and unconditional logistic regression,etc.to analyze the associations of pre-pregnancy BMI,GWG/BMI gain with each physical development index of the infants and the risk of overweight/obese at each stage.The associations were also evaluated by stratifying pre-pregnancy BMI.3.Part Three:Women with good pregnancy outcomes from the cohort of Part One were took as reference population and the percentile method was used to determine the recommended range of pre-pregnancy BMI,GWG and BMI gain.Restricted Cubic Spline(RCS)was conducted to evaluate the continuous change of odds ratio for LBW,macrosomia,preterm birth as pre-pregnancy BMI increased.The recommendations of GWG and BMI gain in our study were compared with IOM recommendations,and the risk of LBW and macrosomia was evaluated using different recommendations.Results:1.Part One:(1)The prevalence rate of LBW,macrosomia,SGA and LGA were 2.66%.6.59%?3.39%and 28.05%respectively.There were significant positive correlations of pre-pregnancy BMI,GWG,BMI gain with neonatal birth weight and PI value(all Ps<0.01).Pre-pregnancy underweight increased the risk of LB W(OR= 1.25,95%CI:1.11-1.42)and SGA(OR= 1.45,95%CI:1.32-1.59),while the risk of fetal macrosomia and LGA increased among pre-pregnancy overweight and obese women.GWG below the IOM recommendation increased the risk of LBW(OR=1.35,95%CI:1.20-1.52)and SGA(OR=1.37,95%CI:1.24-1.51),while GWG above the IOM recommendation was a risk factor of macrosomia(OR=2.34,95%CI:2.18-2.51)and LGA(OR=1.85,95%CI:1.78-1.92);As pre-pregnancy BMI increased,the risk of macrosomia and LGA was elevated,and the risk of LBW and SGA decreased.(2)Pre-pregnancy underweight,overweight and obese were all related to the elevated risk of PTB,and the OR was highest among women who were obese prior to pregnancy(OR=2.22,95%CI:1.64-3.02).Inadequate GWG might increase the risk of PTB while excessive GWG was related to the decreased risk of PTB.The risk of PTB decreased as gestational BMI gain increased.Further analysis by different subtypes of PTB showed that pre-pregnancy underweight was related to the increased risk of spontaneous PTB,but had no significant relation with PPROM or medically indicated PTB.Pre-pregnancy overweight and obese increased the risk of all the three subtypes of PTB.The risk of spontaneous PTB and PPROM increased when GWG was inadequate.As gestational BMI gain increased,risk of the three subtypes of PTB decreased.(3)New born infants whose mothers were obese prior to pregnancy had the lowest Apgar score at 1 minute of birth(P<0.01);As maternal GWG increased,infants' Apgar score at 1 minute and 5 minutes significantly increased(P<0.05).Among all the maternal pre-pregnancy BMI categories,infants whose mothers were obese before pregnancy had the highest rate of birth asphyxia(2.67%),however,there was no significant association between maternal pregnancy obese and elevated risk of newborn birth asphyxia.The risk of birth asphyxia was increased when the GWG was inadequate(OR= 1.34,95%CI:1.18-1.52);As gestational BMI gain increased,the risk of birth asphyxia gradually decreased.When stratified by pre-pregnancy BMI,inadequate GWG was shown to be related to the elevated risk of birth asphyxia among women who had normal weight prior to pregnancy(OR=1.37,95%CI:1.19-1.58),and excessive GWG decreased the risk of birth asphyxia among women who were underweight prior to pregnancy(OR=0.75,95%CI:0.58-0.97).Among women who were underweight or normal weight before pregnancy,risk of birth asphyxia significantly decreased as gestational BMI gain increased.(4)Pre-pregnancy overweight(OR=1.63,95%CI:1.51-1.75)/obese(OR=2.38,95%CI:1.91-2.96)and excessive GWG(OR=1.43,95%CI:1.38-1.47)were all related to the significant elevated odds of cesarean section.The odds of cesarean section gradually increased as the gestational BMI gain increase.Excessive GWG significantly increased the odds of cesarean section across all the pre-pregnancy BMI categories.2.Part Two:(1)There were significant positive associations between maternal pre-pregnancy BMI,GWG/BMI gain and the level of infants' weight,height,head circumference and BMI at each stage(P<0.01).As maternal pre-pregnancy BMI,GWG/BMI gain increased,WAZ?LAZ.?HCZ and BAZ of the infants at each stage correspondingly increased.Results of generalized linear regression analysis demonstrated that after adjusting for the potential confounders such as birth weight and gestational age,etc.,infants whose mother were underweight before pregnancy had lower level of WAZ and BAZ at each stage.On the contrary,infants whose mother were overweight/obese before pregnancy had higher level of WAZ and BAZ at each stage.Maternal inadequate GWG decreased the infants'WAZ and BAZ,while excessive GWG increased the infants' WAZ and BAZ at each stage.Along with the increasing level of maternal BMI gain during pregnancy,infants' WAZ and BAZ increased at each stage.(2)The total prevalence rate of overweight/obese at each stage of the infants was over 30%.After adjusting for the potential confounders such as birth weight,etc.,the risk of infants overweight/obese at each stage significantly increased along with the increasing level of maternal pre-pregnancy BMI,GWG/BMI gain.After stratifying the maternal pre-pregnancy BMI,excessive GWG was significantly associated with the risk of infants overweight/obese at 1 month,across all the pre-pregnancy BMI categories.Among women who were underweight or normal weight prior to pregnancy,excessive GWG significantly increased the risk of infants overweight/obese during 6-24 months.3.Part Three:According to the percentile distribution of the reference population,the recommended range of pre-pregnancy BMI was 19.0-21.5 kg/m.The results of RCS model analysis indicated that as the pre-pregnancy BMI increased,the OR(95%CI)for PTB and LBW had a decreasing tendency at the beginning,and then began to increase.The OR(95%CI)for PTB and LBW reached the lowest point when pre-pregnancy BMI was approximately 19.0kg/m2 and 19.5kg/m2 respectively.Compared to the predefined reference point(22.0kg/m2),when pre-pregnancy BMI was within 19.0-21.5 kg/m2,the risk of PTB,LBW and macrosomia were all significantly decreased.Compared to the Chinese BMI reference for normal adults(18.5-24.0 kg/m),when maternal pre-pregnancy was within the recommended range of our study(19.0-21.5 kg/m2),the risk of PTB,LBW and macrosomia were shown to be lower.Our study recommended the range of GWG for pre-pregnancy underweight,normal weight and overweight women as following:14.5-22.0kg,12.0-20.0kg and 9.0-16.5kg;and the recommended range of gestational BMI gain as:5.6-8.4kg/m2,4.7-7.9kg/m2 and 3.5-6.5kg/m2 for pre-pregnancy underweight,normal weight and overweight women,respectively.The results of evaluating the risk of LBW and macrosomia among pre-pregnancy underweight and normal weight women by IOM recommendations and GWG/BMI gain recommendations of our study were similar;however,the recommendations in the present study were more suitable for pre-pregnancy overweight women,especially for evaluating the risk of LBW among pre-pregnancy overweight women.Conclusions:1.Pre-pregnancy BMI and GWG/gestational BMI gain influence the neonatal birth weight and Apgar score,and are independently associated with the risk of several adverse birth outcomes such as LBW,PTB,macrosomia,LGA and SGA,etc.Weight control efforts before and during pregnancy may help to reduce the risk of adverse birth outcomes.2.Maternal pre-pregnancy BMI and GWG/gestational BMI gain are positively associated with children's weight,height,head circumference and BMI at each stage of 0-2 years old.Maternal overweight/obese prior to pregnancy and excessive GWG/BMI gain during pregnancy are both independent risk factors for overweight/obese of 0-2 years' oldchildren.3.To our knowledge,this is the first cohort study of relatively large sample size exploring the recommendations of pre-pregnancy BMI and GWG/gestational BMI gain that are suitable for Chinese women.The recommendations in our study are shown to well predict the risk of PTB,LBW and macrosomia.