Lowered weight gain during pregnancy and risk of neural tube defects amongoffspring

Background Maternal nutritional factors have been implicated in the complex aetiology of neural tube defects (NTD). We investigated whether the amount of weight a woman gained during pregnancy was associated with her risk of delivering an infant with an NTD. Methods We conducted a population-based case-control study within the cohor t of 708 129 live births and fetal deaths occurring in selected California counties in 1989-1991. Face-to-face interviews were conducted with mothers of 538 (88% of eligible) NTD cases (including those electively terminated, stillborn, or liveborn) and with mothers of 539 (88%) non-malformed livebor n controls within an average of 5 months from the term delivery date. Respo ndent-reported weight gain during pregnancy (kg) was analysed. Risks of inf ants having NTD were estimated among women who gained <10kg compared to tho se who gained <greater than or equal to>10kg during greater than or equal t o 38 week gestations. Results Compared to women who gained greater than or equal to 10kg, an incr eased risk for NTD offspring was observed among women who gained <10kg (odd s ratio [OR] = 3.2, 95% CI: 2.3-4.6). The OR was 5.0 (95% CI: 2.6-9.7) amon g those women who gained <5 kg during pregnancy. The increased risk was not attributable to maternal non-use of a multivitamin containing folic acid, diabetes, NTD-pregnancy history, age, race/ethnicity, education, gravidity, alcohol use, cigarette use, prepregnant obesity, low socioeconomic status, dieting, nausea, nor to lower dietary intakes of folate, zinc, energy, pro tein, fat, carbohydrates, and methionine. An increased risk was observed ev en after simultaneous adjustment for most of these factors (OR = 2.2, 95% C I: 1.2-3.8). The risk associated with gaining <10kg was greater for anencep haly, but still elevated for spina bifida. Conclusions We did not have information on weight gain during early pregnan cy. Because weight gain during the relevant embryological period for NTD (f irst month postconception) is relatively small and often variable, it seems less likely that elevated NTD risks indicate a causal association between lowered weight gain throughout pregnancy and abnormal development of the ne ural tube. It seems more likely that lowered weight gain is a consequence o f carrying an NTD-affected fetus. However, what this consequence is and why risk was substantially larger for anencephaly is unknown.