The association between pregnancy weight gain and birthweight: a within-family comparison

Abstract

Background Excessive pregnancy weight gain appears to increase birth weight and the offspring’s risk for obesity later in life. However, this relationship may be confounded by genetic and other shared influences. Methods We used Vital Statistics Natality records to examine all known births in Michigan and New Jersey from 1989 to 2003. Our sample included 513,501 women who had more than one singleton pregnancy and their 1,164,750 offspring. We examined how differences in weight gain that occurred during two or more pregnancies for each woman predicted the birth weight of her offspring, using a within-subject design to minimize confounding. Findings We found a remarkably consistent relationship between pregnancy weight gain and birth weight (β 7.35 [95% CI 7.10–7.59], p < 0.0001). Infants of women who gain more than 24 kg during pregnancy were 148.9 g (CI 141.7–156.0) heavier at birth, compared to infants of women who gained 8–10 kg. The odds ratio of giving birth to an infant greater than 4000 g was 2.26 (2.09 – 2.44) for a woman who gained more than 24 kg during pregnancy, compared to a woman who gained 8–10 kg. Interpretation Maternal weight gain during pregnancy increases birth weight independent of genetic factors. In view of the apparent relationship between birth weight and adult weight, obesity prevention targeted to woman during pregnancy may be warranted.