MATERNAL SMOKING, BODY-MASS INDEX, AND NEURAL-TUBE DEFECTS

The Swedish health registries were used to investigate a possible effe ct on the incidence of neural tube defects (NTDs) of maternal smoking and maternal body mass index (BMI) (kg/m(2)). Among 1,199,701 infants born in 1983-1993 with known smoking exposure in early pregnancy, 621 infants with NTDs were selected. After controlling for year of birth, maternal age, parity, education level, BMI, and immigrant status (yes/ no), a highly significant, protective effect of maternal smoking on th e incidence of NTDs was found. The adjusted odds ratios (OR) and (95% confidence intervals (CI)) for maternal smoking among infants with NTD s (total), anencephaly, and spina bifida were 0.75 (0.61-0.91), 0.49 ( 0.28-0.85), and 0.76 (0.61-0.95), respectively. A protective dose-resp onse effect of smoking was indicated but was not statistically signifi cant. The association between NTDs and maternal BMI found in earlier s tudies was supported. Women with BMI >26.0 were found to be at higher risk of having an infant with NTD compared with women in other BMI cla sses (adjusted OR = 1.35, 95% CI 1.00-1.83). For women with BMI greate r than or equal to 29, the corresponding odds ratio was 1.29 (0.81-2.0 5). No obvious explanation was found, either for the detected associat ion between NTDs and BMI, or for the protective effect of maternal smo king.