Racial differences in birthweight for gestational age and infant mortalityin extremely-low-risk US populations

Using national data, we develop and contrast the birthweight percentiles fo r gestational age by infants of extremely-low-risk (ELR) White and African- American women and examine racial differences in the proportion of small-fo r-gestational-age (SGA) births. We then scrutinise racial variations in inf ant mortality rates of the infants of ELR women. We further compare the inf ant mortality rates of infants at or below the 10th percentile of birthweig ht for gestational age of each race group to determine whether infants with similar restricted fetal growth have comparable risks of subsequent mortal ity. Single live births, 34-42 weeks' gestation, to White and African-Ameri can US-resident mothers were selected from the 1990-91 US Linked Live Birth -infant Death File (n = 4 360 829). Extremely-low-risk mothers were defined as: married, aged 20-34 years, 13+ years of education, multiparae, with av erage parity for age, adequate prenatal care, vaginal delivery, and no repo rts of medical risk factors, tobacco use or alcohol use during pregnancy. Marked racial variation in birthweight percentiles by gestational age was e vident. Compared with ELR White mothers, the risk of an SGA infant was 2.64 times greater for ELR African-American mothers and the risk of infant mort ality was 1.61 times greater. For the ELR group, the infant mortality rates of African-American and White infants at or below the 10th percentile of b irthweight for gestational age of their respective maternal race group were essentially identical after controlling for gestational age. In conclusion , race differences in fetal growth patterns remained after controlling for risk status. Efforts to remove racial disparities in infant mortality will need to develop aetiological pathways that can explain why African-American s have relatively higher rates of preterm birth and higher infant mortality rates among term and non-SGA infants.