The study from researchers at the University of Iowa and health analysts in South America also suggests that infants of African ancestry, alone or mixed, were more likely to be born prematurely than those born of European-only stock. The findings could help policymakers decide how best to bridge the difference in infant health among non-European-ancestry races in South America’s largest and most populous country.
“This suggests that where you live in Brazil makes a difference, and where you live varies to a certain extent by what your ethnic ancestry is,” says George Wehby, associate professor in the UI College of Public Health and the corresponding author of the study published this month in the American Journal of Public Health. “There is some form of segregation and that’s what contributing to low birth weight among these racial groups.”
The researchers examined 8,949 infants born in select hospitals in 15 cities in seven states, between 1995 and 2009. The infants were grouped in four ethnic categories: those of African ancestry; those of African and European ancestry; those of African and other (non-European) ancestry; and those of European-only ancestry. The team focused on whether infants were born prematurely and whether their birth weight was low (less than 2,500 grams or 6 pounds).
The group found that 12 percent of infants with African ancestry had low birth weights, compared to 8 percent of infants of European ancestry. The rate was nearly a percentage point higher for mixed-race infants (mixed African and European ancestry).
While the percentage difference may not seem pronounced, “it means that out of 100 children, there are four more children (of African ancestry) born at a low birth weight,” Wehby says. Viewed another way, children of African origin are one-and-a half times more likely to be born at a low birth weight than their European-only counterparts, Wehby notes.
Preterm birth rates for infants of African or mixed-race ancestry were nearly three to five percentage points higher than the rate for babies with European-only ancestry, the study found.
Previous research has indicated that differences in birth weight and preterm birth rates may be magnified as the child ages, and reflected in overall health, productivity, and earning power.
The researchers looked at a number of factors, such as education, occupation, and prenatal care visits, to explain the difference in low birth weight and the rate of preterm births by ethnic ancestry. They found that mothers of African ancestry have the equivalent of one less prenatal care visit than mothers of European ancestry. Previous studies have shown that more frequent visits to prenatal care professionals improve a baby’s birth weight and lower the risk of problems at birth.
“Our model tells us that if mothers of African ancestry had the same number of prenatal visits as mothers of European ancestry, then that would reduce the disparities between these groups by more than 30 percent for low birth weight and 60 percent for preterm birth rates,” Wehby says. “How you change that is a question that Brazilian policymakers, along with future studies, need to address.”
Geography could well play a role. The study found that differences in geographic location by race explain more than 70 percent of the disparity in low birth weight and preterm birth rates among infants of African and mixed ancestries compared to those of European-only ancestry.
“This suggests there are geographic variations in health-care, social and economic resources that are important for maternal and infant health,” Wehby says.
The researchers note that while their findings are statistically significant, other factors could contribute to the difference, most notably smoking, which was not analyzed in this study.
By:Richard C. Lewis
Kwame Nyarko, a graduate student at the UI, is the first author on the paper. Jorge Lopez-Camelo and Eduardo Castilla, from the Estudio Colaborativo Latino Americano de Malformaciones Congenitas, are contributing authors.
The National Institutes of Health (grant no.: R03 DE018394) and the National Institute of Dental and Craniofacial Research (grant no.: R03 TW008110) funded the work.
University of Iowa