The effect of parental race on fetal and infant mortality in twin gestations

Previous work has found that singleton birth outcomes are better if the father is black and the mother is white than if the father is white and the mother is black. We sought to examine the effects of parental race on fetal and infant mortality in twins. We analyzed the fetal and infant mortality rates in four groups [both parents white (W-W), both parents black (B-B), father black and mother white (FB-MW), and father white and mother black (FW-MB)], using the 1995--1997 U.S. twin registry data (249,221 twins). Compared to W-W, the infant mortality for B-B, FW-MB, and FB-MW (respectively, relative risk [RR] 1.84, 95% confidence interval [CI] 1.73-1.95; RR 1.39, 95% CI 1.03-1.51; and RR 1.49, 95% CI 1.26-1.77) were all significantly different from W-W but not from each other. When fetal mortality was added to infant mortality, the combined mortality was highest for B-B (RR 1.66, 95% CI 1.58-1.75), intermediate for FW-MB (RR 1.18, 95% CI 0.92-1.51) and FB-MW (RR 1.37, 95% CI 1.19-1.58) and lowest for W-W. Thus, twin infants born to black parents have higher risk of fetal and infant mortality compared with twin infants born to white parents and infants of mixed race parents generally have intermediate outcomes.