Background: The rising rate of macrosomia in the United States is a public health concern, and infants in certain ethnic groups are disproportionately affected.

Objective: To examine the independent effects of race and nativity on fetal macrosomia (birthweight [BW]≥4000 g).

Methods: We requested 2011-2013 US natality data from the CDC to compare incidence of macrosomia across 6 groups of primiparous White, Black, and Latina women, divided by nativity (US-born [USB], foreign-born [FB]); infants were singletons with gestational age 37-42 weeks and BW≥3000 g (N=1,791,718). We created 4 logistic regression models to generate odds ratios (ORs) for effect of maternal race and nativity on macrosomia, adjusting for risk factors in a stepwise progression.

Results: Incidence of macrosomia was highest (10.7%) among USB non-Latina White women (n=122,282) and lowest (5.7%) among USB non-Latina Black women (n=9,861; P<0.0001). Interestingly, compared to their USB counterparts, FB non-Latina Black women were 47% more likely to have a macrosomic infant while FB non-Latina White women were 10% less likely. Nativity had little effect on incidence of macrosomia among Latina women. In all 4 models, adjusted odds for macrosomia were highest for USB non-Latina White women. In the final model, which adjusted for all known risk factors, odds for macrosomia were highest for USB non-Latina White women and lowest for USB non-Latina Black women (OR: 0.53; Cl: 0.52-0.55).

Conclusion(s): Race and nativity are independently associated with giving birth to a macrosomic infant, with highest odds for US-born non-Latina White women after adjusting for all significant risk factors.