Pre-pregnancy BMI And Pregnancy Outcomes: A Population Based Nested Case Control Study

Objectives Pre-pregnancy BMI is very important for the pregnant women and the fetus,which has an adverse effect on recent period and even whole life long . This study was to describe the distribution and the reference percentile charts of pre-pregnancy BMI in Anhui province, China, and then to assess the effect of pre-pregnancy BMI on the 5 adverse birth outcomes (LGA, SGA, LBW, macrosomia, and congenital heart disease).Methods The subjects were consisted of 20 308 pregnant women from 8 study sites, who take routine prenatal health care at local Maternity and Child Care Centers from October 2008 to October 2010. Informations about sociodemographic characteristics, previous pregnancy history, and disease history were collected by Pregnancy Maternal and Child Health Record Form. In addition, pregnant women's height was measured by specially trained medical personnel and their self-reported lowest weight of one year before pregnancy was regarded as pre-pregnancy weight. The percentile curves pre-pregnancy BMI was established using LMS method with the assistance of LMSchartmarker Pro version 2.4. The effects of sociodemographic characteristics (registered residence/per capita household income/ education) on pre-pregnancy BMI were analyzed by One-Way ANOVE or Nonparametric Tests, through SPSS10.0.Followed enrolled pregnancy women until delivery, birth outcomes were collected by Pregnancy Maternal and Child Health Record Form and Birth Defects Registration Card. One-Way ANOVE or Nonparametric Tests were used again to find out the effects of on birth index, such as birth weight, height, head circumference, chest measurement and gestational weeks. The relationships between pre-pregnancy BMI and SGA, LGA, LBW and macrosomia were evaluated by chi-square analysis and non-condition logistic regression with design of non-matched nested case-control study. The association of pre-pregnancy BMI and congenital heart disease was analyzed by chi-square and non-condition logistic regression with design of matched nested case-control study.Results There were 20 308 pregnant women were enrolled in the cohort from October 2008 to October 2010. Finally 12 355 women were fellowed up outcomes, of them 7 509 women from Heifei and Maanshan.Out of these 20 308 women in Anhui, the average of pre-pregnancy BMI was 20.17±2.325 kg/m~2. Pre-pregnancy BMI of non primigravida was higher than that of primipara (t=-5.857 , P<0.001). Pregnant women with per capita household income<1000 yuan had the higher pre-pregnancy BMI than other 3 groups (P<0.001).Compare pre-pregnancy BMI based on different degree education, junior high school and below was related to highest pre-pregnancy BMI, the next was bachelor and above and high school or technical school or junior college related smaller high pre-pregnancy BMI (P<0.01).After analyse the birth outcomes of 12 355 pregnant women, it was seen that the pre-pregnancy BMI order of infant with birth weight, body height, head circumference and chest circumference from high to low were: obesity or overweight > normal weight > low body weight (P<0.05).Using unmatched nested case-control study, after adjusted confounding factors (age, registered residence, and pregnant times), to figure out the relationship between pre-pregnancy BMI and gestational age and birth weight. It was seen that pre-pregnant underweight increased the risk of SGA(OR=1.320,95%CI:1.068～1.631), decreased the risks of LGA and macrosomia (OR=0.670,95%CI:0.543～0.678 and OR=0.543,95%CI:0.458～0.643), and had no statistically significant correlations with LBW. Pre-pregnant overweight and obesity increased the risks of LGA(OR=1.758,95%CI:1.503～2.056) and macrosomia (OR=1.870,95%CI:1.540～2.271), and decreased the risk of LBW(OR=0.388,95%CI:0.159～0.950), and had no statistically significant correlations with SGA.By the design of 1:2 matched nested case-control study, we used the data of 7 509 women who were followed the birth outcomes, from which 74 births filled birth defect registration cards, to find out pre-pregnant overweight and obesity were more likely to have baby with congenital heart disease, the OR is 3.600 (95%CI:1.210～10.707).Conclusions Pre-pregnancy BMI could effect birth outcomes. The results suggests that strengthening premarital health careand optimizing pre-pregnancy BMI should reduce adverse birth outcomes.MeSHλmedian coefficient of variation/maternal obesity/body mass index / pregnant women/congenital heart disease/macrosis/small for gestational age/large for gestational age/nested case-control studies...