Are obese women at higher risk for producing malformed offspring?

Our purpose was to determine whether obese women and underweight women have an increased risk of birth defects in their offspring.

A geographically based case-control study of women living in California and Illinois was performed. There were 499 mothers of offspring with neural tube defects, 337 mothers of offspring with other major birth defects, and 534 mothers of offspring without birth defects who participated.

Compared with women of normal weight, women who were extremely obese before pregnancy (body mass index > or = 31 kg/m2) showed a significantly increased risk of having an infant with a neural tube defect (odds ratio 1.8, 95% confidence interval 1.1 to 3.0), especially spina bifida (odds ratio 2.6, 95% confidence interval 1.5 to 4.5), after adjustments for age, race, education, and family income. Obese women also had significantly increased risks (p < 0.05) of having an infant with other defects of the central nervous system, great vessel defects, ventral wall defects, or other intestinal defects.

Our data suggest that offspring of obese women (but not underweight women) are at an increased risk of neural tube defects and several other malformations. If these findings are confirmed, further research will be necessary before it can be concluded that weight reduction before pregnancy will lower the risk of birth defects among obese women. Until then, obese women can address their risk of birth defects with the same measures that are recommended for all women, such as adequate daily intake of folic acid and alpha-fetoprotein screening to identify malformed fetuses.