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Prepregnancy BMI strongly related to infant mortality

Primary care physicians should focus on reducing obesity among women of reproductive age, as data recently published in Obstetrics and Gynecology has indicated there is a strong relation between prepregnancy BMI and infant mortality.

“Concerns with maternal obesity are relatively recent in conjunction with rising rates of obesity in U.S. society, but clinicians, dating back to the 1940s, have warned of the relationship between maternal obesity and poor infant outcomes,” Eugene Declercq, PhD, professor and assistant dean of the community health sciences department at Boston University School of Public Health, and colleagues wrote. “The most recent estimate of rates of obesity among adult women 20 to 39 years of age in the United States was 31.8%; prepregnancy obesity rates in the United States have been estimated at 20% in recent years.”

To analyze any relationship between BMI at prepregnancy and infant mortality, and whether adhering to weight gain recommendations counteracts any such relationship, the researchers conducted a cohort study using 2012 and 2013 U.S. national birth certificate and infant death files from 38 states and the District of Columbia, along with maternal BMI figures. Included in the study were 6,419,836 singleton births and 36,691 infant deaths.

Prenatal weight gain in three categories was based on adherence to the Institute of Medicine’s 2009 revised recommendations. The outcome measure was infant deaths in the first year of life, either in the neonatal period (less than 28 days) or in the postneonatal period (28 days to 1 year). The researchers used the standard definitions for BMI categories.

According to the researchers, using normal pregnancy weight as a reference and adjusting for cofounding factors, the odds ratio for an infant death increased from 1.32 (95% CI, 1.27-1.37) for mothers in the obese I category (BMI of 30-35) to 1.73 (95% CI, 1.64-1.83) for those in the obese III category (BMI of 40 or more). In addition, the adjusted odds ratio for the risk of an infant death among singleton, term, vortex births for mothers who were gaining less than the recommended amount of weight was 1.07 (95% CI, 1.01-1.12). For mothers gaining more weight than recommended, the odds ratio was 1.04 (95% CI, 0.99-1.09).

“This study, in conjunction with others that have demonstrated an association of maternal obesity with increased risk of perinatal death and infant mortality, builds a convincing foundation for future studies of perinatal outcomes for women who were obese and attained a normal or more normal BMI before conception,” Declercq and colleagues wrote. “If such studies demonstrate that preconception weight loss is associated with improved outcome, even if the mechanism underlying that improvement is unknown, a public health campaign encouraging preconception weight loss to benefit not only the maternal but also the fetal and neonatal outcomes would be scientifically grounded, feasible and compelling.” – by Jason Laday

Disclosure: The authors report no relevant financial disclosures.