The limited available data have been unable to distinguish between a black infant birth weight disadvantage related to sociologic variables and that associated with hypothesized genetic factors. We used 1985-1988 Illinois vital records to determine the birth weight distribution of infants delivered to sub-Saharan African-born and U.S.-born black mothers. Distribution of births across the entire birth weight range was similar between babies of white and African-born women. Babies of U.S.-born black women had a distinctly different pattern with births toward lower weights by some 300 grams. The low birth weight (<2500g, LBW) rate was 15% for infants with U.S.-born black mothers(N=34,138) and 8% for infants with African-born black mothers (N=687) compared to 6% for infants with U.S.-born white mothers (N=34,998); OR=2.9(2.7-3.1) and 1.4(1.1-1.9), respectively. Traditional measures of socioeconomic status and reproductive history differed between the subgroups. However, “low risk” U.S.-born black mothers had a significantly greater proportion of moderately low birth weight (1501-2499g) and very low birth weight (≤ 1500g) infants than either U.S.-born white or African-born black mothers of similar risk status (Table). We conclude that black(compared to white) infants have lower birth weights only when the mother is U.S.-born. This implies that hypothesized genetic factors do not contribute significantly to the black-white disparity in birth weight distribution, since at least 30% of the genes in U.S.-born blacks are of European origin, presumably more than African-born blacks.

Table 1
Full size table