Intertwin birthweight discordance and parental race: a retrospective cohort study.

Objectives: Previous studies examined the association of maternal race with pregnancy outcomes. The study aimed to examine the effects of maternal, paternal, and parental race on intertwin birth weight discordance.Methods: We used the 2011-2015 multiple birth files of the USA for this study. The exposure variable of this study was parental race and intertwin birthweight discordance >25% was the outcome. In addition to separately analyzing maternal and paternal races, we assessed the effect of the combined race after grouping the participants into nine groups based on the race of both parents.Results: A total of 203,872 pairs of twins were included in the final analysis. The overall incidence of intertwin birthweight discordance in this population was 7.8%. Birthweight discordance was significantly associated with maternal, paternal, and parental races. Twins born to Black parents had significant risks of developing birthweight discordance than twins born to White parents (adjusted OR = 1.11, 95% CI: 1.06-1.17 for Black mothers and Black fathers). Combined parental race showed that compared to twins born to both parents Whites, twins born to both parents Blacks had a significantly elevated risk of developing birthweight discordance (adjusted OR = 1.13, 95% CI: 1.07-1.18). No significant difference in the risk of developing birthweight discordance was found for other parental race groups, same race or different race parents.Conclusions: Twins born to Black mothers, fathers, or both parents had significant risks of developing intertwin birthweight discordance than twins born to White mothers, fathers, or both parents.