title: Race Disparities and Decreasing Birth Weight: Are All Babies Getting Smaller?
abstract: The mean infant birth weight in the United States increased for decades, but it might now be decreasing. Given race disparities in fetal growth, we explored race-specific trends in birth weight at Magee-Womens Hospital, Pittsburgh, Pennsylvania, from 1997 to 2011. Among singleton births delivered at 37-41 weeks (n = 70,607), we evaluated the proportions who were small for gestational age and large for gestational age and changes in mean birth weights over time. Results were stratified by maternal race/ethnicity. Since 1997, the number of infants born small for their gestational ages increased (8.7%-9.9%), whereas the number born large for their gestational ages decreased (8.9%-7.7%). After adjustment for gestational week at birth, maternal characteristics, and pregnancy conditions, birth weight decreased by 2.20 g per year (P < 0.0001). Decreases were greater for spontaneous births. Reductions were significantly greater in infants born to African-American women than in those born to white women (-3.78 vs. -1.88 per year; P for interaction = 0.010). Quantile regression models indicated that birth weight decreased across the entire distribution, but reductions among infants born to African-American women were limited to those in the upper quartile after accounting for maternal factors. Limiting the analysis to low-risk women eliminated birth weight reductions. Birth weight has decreased in recent years, and reductions were greater in infants born to African-American women. These trends might be explained by accumulation of risk factors such as hypertension and prepregnancy obesity that disproportionately affect African-American women. Our results raise the possibility of worsening race disparities in fetal growth.
authors.forename: Janet M
authors.initials: JM
authors.lastname: Catov
authors.forename: MinJae
authors.initials: M
authors.lastname: Lee
authors.forename: James M
authors.initials: JM
authors.lastname: Roberts
authors.forename: Jia
authors.initials: J
authors.lastname: Xu
authors.forename: Hyagriv N
authors.initials: HN
authors.lastname: Simhan
mesh_terms: D001741:Black or African American / Q000706:statistics & numerical data*; D001724:Birth Weight; D036861:Delivery, Obstetric / Q000379:methods; D005260:Female; D047109:Fetal Development; D005865:Gestational Age; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D008297:Male; D010414:Pennsylvania / Q000453:epidemiology; D012307:Risk Factors; D012737:Sex Factors; D012959:Socioeconomic Factors; D044465:White People / Q000706:statistics & numerical data*
keywords: birth weight; growth restriction; macrosomia; obesity