Jennifer Garcia
January 21, 2016
A higher maternal body mass index (BMI) is associated with an increased risk for infant mortality, according to a new cohort study published in the February issue of Obstetrics & Gynecology.
The study, led by Eugene Declercq, PhD, from the Boston University School of Public Health in Massachusetts, evaluated US national linked birth certificate and infant death files from 2012 and 2013. They analyzed data from 6,419,836 singleton births and 36,691 infant deaths spanning 38 states and the District of Columbia and included the mother’s prenatal BMI and gestational weight gain. BMI categories were defined as follows: normal weight: BMI, 18.5 to less than 25 kg/m2; overweight: BMI, 25 to less than 30 kg/m2; obese I: BMI, 30 to less than 35 kg/m2; obese II: BMI, 35 to less than 40 kg/m2; and obese III: BMI of 40 kg/m2 or higher.
The overall infant mortality rate among this cohort was 5.72 per 1000 live births, but rose with rising maternal BMI to 5.9 for obese I mothers (P < .001) and to 8.2 for obese III moms (P < .001).
Moreover, the authors found that the odds ratio for infant death rose from 1.32 (95% confidence interval [CI], 1.27 – 1.37) for mothers in the obese I category compared with normal-weight mothers to 1.73 (95% CI, 1.64 – 1.83) for obese III mothers in multivariate logistic regression models adjusted for maternal age, ethnicity, education, live birth order, and the presence of comorbidities.
The authors found these associations to be present even after other causes of infant death were also evaluated. When evaluated in association with causes of infant mortality, the authors found that infant mortality for preterm-related causes increased with increasing BMI and was twice as high among obese compared with normal-weight mothers (P < .001). Infant deaths from congenital anomalies were also more common among mothers in the obese category compared with normal-weight mothers (P < .001), as were “sudden unexpected infant deaths” among women in the obese categories (P < .001).
When the authors stratified infant mortality into neonatal (<28 days) and postnatal (28 days – 1 year) categories, adjusting for confounders, a consistent increase in the overall risk for infant death remained across BMI categories, with infants born to mothers in the obese III category having “a significantly higher risk of death in the first 28 days (74% higher), from 28 days to 1 year (51% higher), and overall in the first year (73% greater).” The researchers also found that, among mothers who gained less than the Institute of Medicine recommended weight, the odds ratio for the risk for infant death was 1.07 (95% CI, 1.01 – 1.12), whereas for those gaining more than the recommended weight, it was 1.04 (95% CI, 0.99 – 1.09).
Although these findings are similar to what has been noted in previous studies, prior studies did not include cause-of-death and weight-gain data or included less diverse populations. The researchers acknowledge, however, that the data in this study may not accurately represent all US births because data from 12 states were not included.
The authors note that whether preconception weight loss efforts would decrease the risk for infant mortality among obese women remains unclear; however, results of this study underscore the need for further “research into the benefits of a systemwide effort to prevent obesity among women of reproductive age.”
The authors have disclosed no relevant financial relationships.
Obstet Gynecol. 2016;127:279-287. Abstract