Risk of neural tube defect-affected pregnancies among obese women.

OBJECTIVE

To investigate the risk for neural tube defect (NTD)-affected pregnancies among obese women (ie, women with a body mass index [BMI] > 29kg/m2) compared with women of average prepregnancy weight.

DESIGN

Population-based case-control study.

SETTING

All hospitals in 55 of 58 counties in California.

PARTICIPANTS

In-person interviews were conducted with mothers of 538 (88% of eligible) NTD cases (including fetuses and infants electively terminated, stillborn, or born alive) and with mothers of 539 nonmalformed controls (88%) within an average of 5 months from the term delivery date.

MAIN OUTCOME MEASURES

The risk of an NTD-affected pregnancy among obese women.

RESULTS

Compared with women whose BMI was less than or equal to 29 kg/m2, an increased risk for NTD-affected pregnancy was observed among obese women (odds ratio, 1.9; 95% confidence interval, 1.3 to 2.9). The increased risk was not attributable to maternal nonuse of a vitamin containing folic acid, diabetes, use of diet pills, lower dietary folate intake, or an NTD-pregnancy history. Adjustment for maternal age, education, gravidity, use of vitamins, and use of alcohol did not change the odds ratio. The risk associated with maternal obesity was greater for spina bifida and for other less prevalent NTDs than for anencephaly.

CONCLUSION

Because as many as 10% of women may be obese periconceptionally, the observed twofold increased risk is relevant to the population burden of NTDs.