Pediatric paradox: heterogeneity in the birth cohort.

Comparisons of birth-weight-specific infant mortality indicate that low-birth-weight African American infants have lower mortality than low-birth-weight European American infants despite higher infant mortality overall-the "pediatric paradox." One explanation is heterogeneity in birth weight. Analyses of African American and European American births suggest that birth cohorts consist of two heterogeneous subpopulations. One appears to account for normal births, whereas the other may consist of compromised births. Estimates of infant mortality indicate that the compromised subpopulation has higher overall mortality but lower birth-weight-specific mortality. We attribute lower birth-weight-specific infant mortality in the compromised subpopulation to higher rates of fetal loss. Compared to European American birth cohorts, African American birth cohorts have (1) higher birth-weight-specific mortality in the normal subpopulation, (2) larger compromised subpopulations, and (3) lower birth-weight-specific mortality in the compromised subpopulation. Consequently, the pediatric paradox is attributable to greater rates of compromised pregnancies and higher fetal losses among African Americans.