Prepregnancy Body Mass Index and Infant Mortality in 38 U.S. States, 2012-2013

Objective: To estimate whether prepregnancy body mass index (BMI) is related to infant mortality and whether adherence to weight gain recommendations mitigates the relationship between BMI and infant mortality.

Methods: This was a cohort study using 2012-2013 U.S. national linked birth certificate and infant death files for 38 states and the District of Columbia with the BMI measure, including 6,419,836 singleton births and 36,691 infant deaths (infant mortality rate 5.72/1,000). Prenatal weight gain in three categories was based on adherence to Institute of Medicine recommendations. The outcome measure was infant deaths in the first year of life subdivided into two time periods: neonatal (less than 28 days) and postneonatal (28 days to 1 year).

Results: With normal prepregnancy weight as a reference, after adjustment, the odds ratio (OR) for an infant death rose from 1.32 (95% confidence interval [CI] 1.27-1.37) for mothers in the obese I category to 1.73 (95% CI 1.64-1.83) for obese III. Higher BMI was related to higher rates of both neonatal and postneonatal mortality. The adjusted OR for the risk of an infant death among singleton, term, vertex births for those gaining less than the recommended weight was 1.07 (95% CI 1.01-1.12) and 1.04 (95% CI 0.99-1.09) for those gaining more than recommended.

Conclusion: Even after controlling for multiple risks, prepregnancy BMI was strongly related to infant mortality. Efforts to lower the infant mortality rate may benefit from a focus on reducing obesity among women of reproductive age.