| ObjectiveWith the implementation of the new fertility policy,the number of women planning to have more children in China has further increased,so it is important to further clarify the association between body mass index(BMI)and reproductive health level among women with successive pregnancies.The aim of this study was to analyze the association between BMI levels and changes in BMI and adverse maternal outcomes in women with two successive pregnancies.MethodsUsing a population-based retrospective cohort study,1 718 243 women aged 20-49 years planning to become pregnant who participated in the National Free Pre-Pregnancy Check-ups Project(NFPCP)twice successively between 2010 and 2020were selected,using the BMI measured at the time of both enrolments as exposure,to analyze the association between mean BMI and the occurrence of infertility at least once,both times,and mean waiting time to pregnancy(TTP)were analyzed separately.Kaplan-Meier survival curves for mean BMI classification were plotted with pregnancy as a censored event and Log Rank tests were performed between groups.The bias regression coefficientβand its 95%confidence interval(CI)between the amount of change in BMI and the amount of change in TTP were analyzed using generalized linear regression.Among the 479 279 study subjects who did not experience infertility in their first pregnancy preparation,the association between change in BMI category,amount of change in BMI and infertility,and TTP was analyzed and stratified according to first BMI.The study also selected 354 274 pregnant women aged 20-49 years who participated in the NFPCP for two successive pregnancies between 2010 and 2020 and were pregnant,and analyzed the association between mean BMI during two successive pregnancies and the occurrence of at least one and both Adverse Pregnancy Outcomes(APO),respectively.The association between mean BMI over two successive pregnancies and the occurrence of at least and both APO was analyzed[APO includes spontaneous abortion,preterm birth,low birth weight(LBW),Small for Gestational Age(SGA),large for Gestational Age(LGA),Any Adverse Pregnancy Outcomes(AAPO)and Multiple Adverse Pregnancy Outcomes(MAPO)].In each of the different APO analyses,the association between the change in BMI category and the amount of BMI change and the occurrence of APO in the second pregnancy was analyzed in subjects who did not have the APO in the first time,and the analysis was stratified according to the first BMI;the association between the change in BMI category and the amount of BMI change and the absence of APO in the second pregnancy was also analyzed in subjects who had the APO in the first time,and the analysis was stratified according to the first BMI.The association between the change in BMI category and the amount of BMI change and the absence of APO in the second pregnancy was analyzed and stratified according to the first BMI.When the outcome was dichotomous infertility,APO,the Odds Ratio(OR)and its95%CI were estimated using unadjusted,age-adjusted,and multivariate-adjusted logistic regression,and Restricted Cubic Spline(RCS)based on multivariate-adjusted logistic regression was used.When exposure was an ordered categorical variable,a simple linear.When exposure was an ordered categorical variable,a simple linear regression was used to test for linear trends between the group median values of the exposure subgroups and the indicators of association.Results1.compared to those with normal weight,the risk of at least one infertility during successive pregnancy preparation was increased in those who were underweight,overweight and obese,with a OR(95%CI)of 1.17(1.15-1.20),1.16(1.14-1.18)and1.53(1.46-1.60),respectively,and the risk of infertility on both occasions was 0.95(0.94-0.96),1.07(1.06-1.08)and 1.26(1.24-1.29);the increased risk of delayed mean TTP had a TR of 1.05(1.04-1.05),1.08(1.07-1.09)and 1.19(1.17-1.20),respectively.2.Using a normal weight before and after two successive pregnancy preparations as a reference,study subjects who remained underweight,overweight and obese before and after had an increased risk of infertility with a multivariate-adjusted OR(95%CI)of 1.30(1.26-1.34),1.17(1.13-1.22)and 1.51(1.40-1.63),respectively,and were additionally found to have a TTP had delays with multivariate-adjusted TR(95%CI)of 1.20(1.17-1.23),1.15(1.12-1.19)and 1.27(1.19-1.35),respectively.The fertility of the study subjects decreased when BMI was elevated by one level during two successive pregnancy preparations.In contrast,fertility increased when the BMI class decreased in the study subjects who were overweight the previous time.3.In the overall population,those with normal weight and overweight first pregnancy preparation BMI,an increase in BMI of more than 1 kg/m~2 can lead to a delay in TTP compared to the group with a change in BMI of[-1,1)kg/m~2 during two successive preparations.However,in subjects with a underweight for the first pregnancy,an increase in BMI of more than 1 kg/m~2 during two successive pregnancies improved fertility.For all study subjects except those with underweight in the first pregnancy preparation,a decrease in BMI of more than 1 kg/m~2 between two successive pregnancy preparations will increase fertility levels.4.Underweight is associated with an increased risk of preterm birth,LBW,SGA,and AAPO compared to normal weight,and is associated with a decreased risk of macrosomia,LGA,and MAPO,and possibly an increased risk of spontaneous abortion.Pre-pregnancy overweight and obesity are risk factors for macrosomia,LGA,AAPO,MAPO,and are protective factors for SGA.5.Using two successive pregnancies with normal pre-pregnancy BMI as a reference,both underweight increased the risk of spontaneous abortion,preterm birth,LBW,SGA,and AAPO,and decreased the risk of macrosomia and LGA;both overweight and obese BMIs increased the risk of macrosomia,LGA,MAPO,and decreased the risk of SGA;in addition,both obese BMIs increased the risk of The risk of AAPO was also increased by obesity in both pregnancies.The risk of spontaneous abortion,preterm birth,LBW,SGA,and AAPO increased,and the risk of LGA was decreased in the second pregnancy compared to the reference group when the BMI categories shifted between two successive pregnancies to underweight-normal and normal-underweight.In subjects with normal and overweight BMI before first pregnancy,it was found that a decrease in BMI to too low would result in a decreased risk of macrosomia and LGA development compared to keeping the BMI category constant before and after;whereas an increase in BMI class resulted in an increased risk of macrosomia and LGA development,while leading to a decreased risk of SGA development.6.Compared to a change in BMI of[-1,1)kg/m~2 between two successive pregnancies,an increase in BMI of 3 kg/m~2 or more reduces spontaneous abortion[a OR:0.81(0.74-0.88)],preterm birth[a OR:0.92(0.87-0.98)],LBW[a OR:0.66(0.57-0.77)],and SGA[a OR:0.82(0.78-0.86)]will increase the risk of occurrence of macrosomia[a OR:1.29(1.21-1.38)],LGA[a OR:1.27(1.22-1.32)]and MAPO[a OR:1.13(1.07-1.19)].The risk of occurrence of macrosomia,LGA and MAPO was reduced in study subjects with a non-excessive underweight in the first pregnancy and a reduction in BMI of more than 1 kg/m~2 between two successive pregnancies.In study subjects with a non-obese first pregnancy,an increase in BMI of more than 3 kg/m~2 between two successive pregnancies will increase the risk of occurrence of macrosomia and LGA,while decreasing the risk of SGA.ConclusionUnreasonable pregnancy preparation or pre-pregnancy BMI levels,successive pregnancy preparation or an unreasonable range of BMI changes between successive pregnancies can increase the risk of adverse maternal events.Women of childbearing age should maintain a healthy preconception or pre-pregnancy BMI level.Women who are still planning a postpartum pregnancy should actively manage their weight between pregnancies,seek postpartum care,and improve their lifestyle to reduce the risk of adverse maternal outcomes and improve their reproductive health. |
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