Maternal obesity, gestational diabetes, and central nervous system birth defects.

BACKGROUND

Maternal obesity and diabetes are both associated with increased risk of congenital central nervous system (CNS) malformations in the offspring and may share a common underlying mechanism. Our objective was to evaluate whether gestational diabetes influenced the association of prepregnancy maternal obesity and risks for CNS birth defects.

METHODS

This Texas population-based case-control study evaluated births occurring January 1997 through June 2001. Data came from structured telephone interviews. Cases (n=477) were mothers of offspring with anencephaly (n=120), spina bifida (n=184), holoprosencephaly (n=49), or isolated hydrocephaly (n=124). Controls (n=497) were mothers of live infants without abnormalities randomly selected from the same hospitals as cases. Response rates were approximately 60% for both cases and controls. We evaluated maternal obesity (body mass index > or =30.0 kg/m) and risks for CNS birth defects, as well as whether gestational diabetes influenced the risks.

RESULTS

After adjusting for maternal ethnicity, age, education, smoking, alcohol use, and periconceptional vitamin use, obese women had substantially increased risks of delivering offspring with anencephaly (odds ratio=2.3; 95% confidence interval=1.2-4.3), spina bifida (2.8; 1.7-4.5), or isolated hydrocephaly (2.7; 1.5-5.0), but not holoprosencephaly (1.4; 0.5-3.8). Odds ratios were higher for the joint effects of maternal obesity and gestational diabetes, with evidence for interaction on a multiplicative scale.

CONCLUSIONS

Maternal obesity and gestational diabetes may increase the risk of CNS birth defects through shared causal mechanisms.