Prepregnancy Body Mass Index, Weight Gain During Pregnancy, and Health Outcomes

Each year, approximately 130 million infants are born worldwide, and there were 3.8 million births in the United States in 2017.¹ Rates of maternal mortality and adverse pregnancy outcomes in the United States are increasing, and abnormal prepregnancy body mass index (BMI) and abnormal gestational weight gain have been associated with these adverse outcomes.

In a recent meta-analysis published in JAMA, Goldstein et al² reported that gestational weight gain exceeded weight gain recommended by the Institute of Medicine (now the National Academy of Medicine) in 47% of 1 309 136 pregnancies. Women with excess gestational weight gain were more likely to undergo cesarean delivery (odds ratio [OR], 1.30 [95% CI, 1.25-1.35]; absolute difference: 4%) and more likely to have infants who were large for gestational age (OR, 1.85 [95% CI, 1.76-1.95]; absolute difference: 4%) or who met criteria for macrosomia (OR, 1.95 [95% CI, 1.79-2.11]; absolute difference: 6%).²

In this issue of JAMA, the LifeCycle Project-Maternal Obesity and Childhood Outcomes Study Group³reports the results of an individual patient-level meta-analysis in which the amount of gestational weight gain associated with fewer adverse pregnancy outcomes was defined according to prepregnancy BMI. Even though the amount of optimal weight gain during pregnancy varied according to prepregnancy BMI, gestational weight gain had only low to moderate discriminative performance for adverse outcomes.

In contrast, prepregnancy BMI values above normal were strongly associated with higher rates of adverse outcomes. These associations were observed regardless of the amount of gestational weight gain. Thus, an important conclusion of the report by Voerman et al³ is that prepregnancy BMI was more strongly associated with adverse maternal and infant outcomes than the amount of gestational weight gain.

Obesity affects 40% of women in the United States.⁴ Ensuring that pregnancies result in healthy mothers and infants is an important public health goal. Based on the study by Voerman et al,³ resources should be dedicated toward ensuring an optimal BMI for all women of reproductive age rather than on gestational weight gain.⁵ Recent guidelines and available services can help achieve this important public health goal.^5,6

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