Background: Case-control studies have consistently suggested an association between pre- or periconceptional maternal obesity and an increased risk for neural tube defects (NTDs). Few studies have examined the association between body mass index (BMI) and NTDs using measured weight and height. We examined this association in a large cohort study in China.Methods: We used data from a large population-based cohort study established to evaluate the effectiveness of folic acid supplementation to prevent NTDs in China. BMI was computed using maternal weight and height measured before pregnancy or during early pregnancy. External birth defects were identified through a unique birth defects surveillance system. We estimated the birth prevalence and prevalence odds ratios (POR) for NTDs by Chinese BMI categories, controlling for potential confounders.Results: Our study population included a total of 194,844 women. We observed significantly elevated risk for spina bifida (adjusted POR = 5.4, 95% CI: 1.3-22.5) among children born to obese compared to normal weight women. Among women who took folic acid supplements, the adjusted POR for spina bifida among obese women was 10.0 (95% CI: 2.3-42.6) compared to pill users who were of normal weight. Borderline significantly elevated risk was observed for anencephaly (adjusted POR = 1.8; 95% CI: 1.0-3.2) among children born to underweight compared to normal weight women.Conclusions: Our findings suggest that maternal periconceptional obesity may be associated with an increased risk for spina bifida. Maternal underweight may be associated with increased risk for anencephaly.
Keywords: Birth defects; body mass index (BMI); maternal obesity; maternal overweight; neural tube defects.