Racial differences in birth weight of term infants in a northern California population

Census data show that an increasing proportion of the population of the United States is of Asian or Hispanic origin. Reference curves used to characterize fetal growth relative to gestational age are predominantly based on data for White infants. The goal of this study was to compare the birth weight distributions for term Asian or Hispanic infants with that for White infants, and to determine whether the prevalence of small (SGA) or large size(LGA) for gestational age differs between Asian or Hispanic and White infants.

A community hospital in Northern California.

Data was collected prospectively from May 1 to September 13, 2000 on all singleton term infants born at this hospital. Gestational age was assessed by the best obstetrical estimate and ethnicity was determined by parental report. Infants were categorized as White, Hispanic, Chinese, Asian Indian, Other Asian, and Other. Birth weights, length, and head circumferences were compared using ANOVA and the Student-Newman-Keuls test. Differences in rates of diagnosis of SGA or LGA were assessed by chi square.

1539 infants were included in the study sample; 30% were White, 21% Asian Indian, 15% Chinese, 9% Hispanic, 7% other Asian, and 18% Other. Asian (Chinese, Asian Indian, or Other Asian), Hispanic, and Other babies had lower mean birth weights, shorter mean lengths, and smaller mean head circumferences than White babies. Asian, Hispanic, and Other male babies were lighter, shorter, and had smaller heads than white male babies. Asian females, but not Hispanic or Other ones, were lighter and had smaller head circumferences than White females; Asian Indian, Other Asian, and Other females had shorter lengths than White female infants. Indian and Other Asian, but not Chinese, babies were more likely than White babies to be SGA; babies in all three Asian groups were less likely than White babies to be LGA.

Failure to account for ethnic differences in intrauterine growth may lead to inaccurate diagnosis of fetal growth abnormalities in infants of Asian ancestry.