Racial and Ethnic Variations in Prepregnancy Body Mass Index and the Risk for Macrosomia in Missouri Infants, 1990-2004

OBJECTIVE: We sought to determine whether an increase in prepregnancy body mass index is associated with macrosomia and whether the association varies by race and ethnicity over time.

METHODS: A population-based cohort study was conducted among 135,526 live infants born to Missouri mothers between 1990-2004. The cohort was divided into three groups: non-Hispanic White, non-Hispanic Black, and all other races. Logistic regression was used to evaluate the association between prepregnancy BMI and macrosomia risk for each race group over time (1990-2004). Adjusted odds ratios (aOR) with 95% confidence intervals (CI) were calculated to measure the strength and precision of all associations.

RESULTS: The percentages of pre-pregnancy overweight and obese women have increased over time for all racial groups. Compared to the normal weight reference group, the odds of delivering a macrosomic infant decreased linearly over time, with a 30% reduction in the odds by 2002-2004, aOR 0.70 (95%CI 0.68-0.73). The odds of delivering a macrosomic infant declined more significantly for non-Hispanic Blacks over time. Weight gain was more associated with an increased risk of macrosomia in non-Hispanic Black women, aOR 2.45 (95% CI 2.4-2.51) compared to non-Hispanic White women.

CONCLUSION: The macrosomia risk declined over time in this study despite increased prepregnancy weight and gestational weight gain in Missouri women considered overweight or obese. While ethnic and racial variations in macrosomia risk were noted, this study more clearly documents racial differences in the declining rates of macrosomia. Further prospective studies are needed to explore the factors associated with the declining macrosomia risk (such as maternal nutritional status) and the underlying racial differences.