To examine associations between pregnancy weight gain outside and within ranges recommended by the Institute of Medicine and birth weight by both prepregnant body mass index (BMI) and race-ethnicity.
Mean birth weight and incidence of term low birth weight (LBW, less than 2500 g) and high birth weight (more than 4500 g) were compared across BMI-pregnancy weight gain-race-ethnicity strata. Subjects were 173,066 white, black, and Hispanic low-income pregnant women attending prenatal nutrition programs between 1990 and 1993.
Among low and average BMI women (all race-ethnicity groups), weight gain within Institute of Medicine ranges resulted in significant LBW reductions; further LBW reductions at gains beyond Institute of Medicine ranges were offset by increasing high birth weight risk. Among women of high and obese BMI, LBW trends were less pronounced; thus, the benefit of gaining within the Institute of Medicine range was less apparent. Although blacks in every BMI-weight gain category had lower mean birth weights than white women, gaining in the upper end of the Institute of Medicine ranges did not provide a consistent LBW reduction for black women; adjusted LBW odds ratios and 95% confidence intervals for gains in the upper relative to the lower half of the Institute of Medicine range were 1.3 (0.8, 2.1), 0.7 (0.5,1.03), 0.3 (0.2, 0.8), and 1.3 (0.7, 2.5) for black women of low, average, high, and obese BMI, respectively.
Institute of Medicine pregnancy weight gain ranges recommended for low and average BMI women appear reasonable, but recommendations for high and obese BMI women require further evaluation. The recommendation that black women in all BMI groups strive for gains toward the upper ends of the ranges is not supported clearly by these data.