Association of interpregnancy change in body mass index and spina bifida

Epidemiologic studies have consistently identified an association between spina bifida and maternal body mass index (BMI). Whether this reflects a causal relationship is unknown. If this association does reflect a causal relationship, the risk of spina bifida should change with changes in maternal BMI. We evaluated the association between spina bifida and maternal change in BMI, assessed using interpregnancy change in BMI (IPC-BMI).

We used data from the Texas Birth Defects Registry and statewide vital records for 248 spina bifida cases and 2,562 controls (2006-2012) to conduct a case-control study. We used logistic regression to estimate the association between IPC-BMI and spina bifida, with adjustment for potential confounders.

When assessed as a continuous variable, IPC-BMI was associated with spina bifida, with a 5% increase in the odds of spina bifida per unit (approximately 6 pounds) increase in BMI (adjusted odds ratios [aOR] = 1.05, 95% CI: 1.02, 1.09). When assessed as a categorical variable, with weight stable women as the referent, the odds of spina bifida were lower in women with any BMI decrease (aOR = 0.73, 95% CI: 0.50, 1.08) and higher in women with an increase of ≥1 BMI units (aOR = 1.17, 95% CI: 0.85, 1.62).

Our findings provide suggestive, although not conclusive, evidence that maternal prepregnancy change in BMI, assessed using IPC-BMI, is associated with spina bifida in the later pregnancy. Additional studies aimed at confirming this association and further strengthening the evidence for a causal relationship between spina bifida and maternal BMI are needed.