Maternal Smoking, Body Mass Index, and Neural Tube Defects

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Abstract
The Swedish health registries were used to investigate a possible effect on the incidence of neural tube defects (NTDs) of maternal smoking and maternal body mass index (BMI) (kg/m2). 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 the incidence of NTDs was found. The adjusted odds ratios (OR) and (95% confidence intervals (Cl)) for maternal smoking among infants with NTDs (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-response effect of smoking was indicated but was not statistically significant. The association between NTDs and maternal BMI found in earlier studies 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 classes (adjusted OR = 1.35, 95% Cl 1.00–1.83). For women with BMI >29, the corresponding odds ratio was 1.29 (0.81–2.05). No obvious explanation was found, either for the detected association between NTDs and BMI, or for the protective effect of maternal smoking. Am J Epidemiol 1998; 147: 1103–11.

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