Documenting and Explaining Birthweight Trends in the United States, 1989-2007

Xiuhong You, University of Texas at San Antonio

Birthweight at either the low or high end of the distribution is associated with adverse health outcomes in later life. This study uses US vital statistics data from 1989 to 2007 to document recent birthweight trends in the US and examines the possible causes behind the trends. Results are reported for all births and by maternal race/ethnicity/nativity. The trend of lower birthweight across the last 18 years is reflected in all birthweight measures: the low-birthweight rate is rising, mean birthweight is declining, and the proportion of macrosomic infants is decreasing. While this trend is most pronounced among US-born non-Hispanic whites and is least pronounced among non-Hispanic blacks, it is common to all race/ethnicity/nativity groups. Regression results suggest that much of the birthweight trend can be explained by shortened gestational age, but common maternal socio-demographic, health and behavioral, and health care and medical intervention factors cannot fully explain the birthweight trend.