Effects Of Prenatal Care And Gestational Weight Gain On Pregnancy Outcomes Using Restricted Cubic Spline

Part I Effects of Prenatal Care on Low Birth Weight Using Restricted Cubic Spline[Objective]To investigate the effects of prenatal care index on low birth weight(LBW), including(1) The dose response effect of two measures of prenatal care index(the number of prenatal care visits and the week of initiation of prenatal care)on low birth weight risk;(2) The synergetic effect of the maternal educational level and two measures of prenatal care on neonatal low birth weight risk.[Methods](1) Data were derived from the Perinatal Health Care Surveillance System(PHCSS) from January 2001 to September 2009 in Kunshan City, Jiangsu Province, eastern China.There were 49327 women who had a delivery. After excluding women with missing or implausible data, macrosomia and so on,the sampling size was 32052, including 31412 women with a normal birth weight delivery and 640 women with a LBW delivery.(2) The number of prenatal care visits was divided into 4 levels: ≤5, 6~8, 9~10, >10(times). The week of initiation of prenatal care was also divided into 4 levels: <9, 9~10, 11~12, >12(week). Continuous variables in different number of prenatal care visits and different initial week of prenatal care were compared using analyses of variance or the rank sum test. The chi-square test was used to compare the difference for the proportion or prevalence between different groups. Multiple logistic modelwas performed to estimate the association including the joint effects with odds ratio(OR) and 95% confidence interval(CI) between the prenatal care measures and LBW risk after adjusting for the potential confounders such as maternal age, gestational age, fetal gender, prenatal care institutions, and so on. The dose-response relationship between the number of prenatal care visits and the risk of LBW was investigated by modeling the quantitative exposure with restricted cubic splines(RCS). [Results](1) Except pregnancy-induced hypertension, the baseline characteristics of pregnant women and their infants according to the number of prenatal care visits were significantly different. And this characteristics were also significantly different among different initial week of prenatal care except pregnancy-induced hypertension and fetal gender. After adjusting for the potential confounders, compared with the women with ≤5 prenatal care visits, the women who had 9-10 visits were less likely to have an LBW newborn(OR=0.52, 95%CI: 0.38-0.71). However, the protective effect was not found among the women with more than 10 visits(OR=0.82, 95%CI: 0.57-1.18). We did not find that the late prenatal care initiation was associated with LBW risk.(2) RCS result showed that the LBW risk displayed a ‘U-shape’ curve tendency among the different number of prenatal care visits(P for nonlinearity=0.0002). In particular, the ORs were approaching the curve’s bottom when the women had 9 or 10 prenatal care visits. Comparing with 5 prenatal care visits, the ORs and 95%CI of LBW risk for 7, 9, 11 and ≥13 visits were 0.92(0.82-1.03), 0.50(0.38-0.66), 0.62(0.47-0.82), and 0.99(0.61-1.60), respectively.(3) There was a significant synergetic effect on the LBW risk between maternal educational attainment and the number of prenatal care visits(χ2=4.98, P=0.0257), whereas no significant maternal educational attainment interaction was found with the week of initiation of prenatal care after adjusting for relevant confounding factors(χ2=2.04, P=0.1530).[Conclusions](1)A “U” trend relationship was showed between the number of prenatal care visits and the risk of LBW, but not the week of initiation of prenatal care.(2) Prenatal care in combination with a higher maternal educational level can produce a protective interaction effect on LBW risk.Part II Effects of Gestational Weight Gain on Caesarean Delivery Using Restricted Cubic Spline[Objective]To investigate the effects of pregnancy overweight and obesity on caesarean delivery, including(1)The effect ofpregnant women body mass index(BMI) of the first prenatal visit and gestational weight gain(GWG) oncaesarean delivery(includingcaesarean delivery during labor and caesarean deliverybefore labor;(2)The dose response effect of GWG(in the form of both classified and continuous variables) on the risks of caesarean deliveryduringand before labor classified by BMIof the first prenatal visit.[Methods](1) Data source was the same as Part I. The inclusion criteria were the newborns were full-term live singletons births and the mother started prenatal care before the 12 th gestational week and finished it after the 37 th gestational week. 18908 women and their baby were included. After excluding women with missing data,caesarean delivery on maternal request and so on, the sampling size was 15758, including 9942 women taking the vaginal delivery, 1110 women taking caesarean delivery during labor, and 4706 women taking caesarean delivery before labor.(2) Pregnant women BMIof the first prenatal visit was regarded as the index of pre-pregnancy overweight and obesity. It was divided into 3 levels according to the Asia criteria: underweight <18.5, normal 18.5~22.9, overweight ≥23(kg/m2). The average weekly weight gain during pregnancy was considered as the index of GWG. It was categorizedinto 4 levelsaccording to the quartile distribution: <0.40 、 0.40~0.50 、0.50~0.60、>0.60(kg/week). Continuous variables in different modes of delivery were compared using analyses of variance or the rank sum test. The chi-square test was used to compare the difference for the proportion or prevalence between different groups. Logistic model was performed to estimate the effect of BMI of the first prenatal visit and GWGon the risks of the caesarean delivery during and before labor. RCSwas used toshow the dose response effect of GWG in the form of continuous variable on the risks of the two modes of caesarean deliveryaccording to the BMI classification for Asia population.[Results](1) Except the week of initiation of prenatal care, a significant difference among three modes of delivery was observed in a number of variables, including not only maternal characteristics, but also neonatal characteristics. The multiple regression model analysis showed that, compared with normal weight women, risks of caesarean delivery during labor and before labor for underweight women were 0.76(0.65-0.89)and 0.76(0.70-0.83); risks for overweight women were 1.43(1.17-1.74)and 1.94(1.73-2.16).(2) Stratification analysis of both Logistic regression and RCS showed that the risks of the two modes of caesarean delivery linear increased with the growing of GWG. But the risks were different for pregnancy women with different BMI of the first prenatal visit. Comparing with GWG <0.40 kg/week, the ORs and 95%CI of caesarean delivery during labor risk for GWG>0.60kg/week1.51(1.00-2.28), 1.45(1.15-1.81), and 2.24(1.37-3.68) in pre-pregnancy underweight, normal, and overweight women; andthe ORs and 95%CI of caesarean deliverybefore laborwere 1.32(1.05-1.65),1.74(1.53-1.99), and 1.80(1.35-2.40), respectively.[Conclusions](1) Pre-pregnancy overweight and obesity and high GWG were the risks of caesarean delivery.(2) The risks of GWG on caesarean delivery were different for pregnancy women with different BMI of the first prenatal visit. And the risk increased with the pre-pregnancy BMI.