Genetics may play a greater role than previously thought in accounting for black women's higher rate of premature births
Experts have long attributed the racial disparity in part to poverty, disparate access to medical care and other environmental factors.
But when the St. Louis researchers adjusted for age, education level, medical and socio-economic factors, black women still had higher rates of premature births and recurrence.
"It's not all one or all the other," said Dr. Louis Muglia, senior author of the study appearing in the February issue of the American Journal of Obstetrics & Gynecology.
Muglia, professor of pediatrics and obstetrics and gynecology at Washington University School of Medicine, wrote that the study suggests black race — independent of other factors — increases risk for extreme pre-term birth and its recurrence in subsequent pregnancies.
Nationally, as well as in Missouri, white women have an 11 percent risk of delivering prematurely while black women have a 19 percent risk.
One outside expert said the large study, which was funded by the March of Dimes, is "very important work" that suggests black women are genetically predisposed to pre-term deliveries.
"The magnitude of the effect is unknown," said Dr. Roberto Romero, chief of the Perinatology Research Branch of the National Institute of Child Health and Human Development, at the National Institutes of Health.
Romero said it calls for more studies to determine the extent to which the phenomenon is genetic, environmental, or both.
Romer said premature birth is the leading cause of infant death among U.S. blacks.
The U.S. ranks 21st for infant deaths among developed nations, he said. The infant mortality rankings by the World Health Organization is one index of public health.
The Washington University researchers analyzed data from a Missouri Department of Health database of all births in the state from 1989 to 1997, adjusting for smoking, poverty and other contributing factors. The data base included more than 700,000 records of births.
The researchers found that black women not only are three times more likely to deliver babies prematurely than white women, they also experience pre-term births earlier in the pregnancy. They also have more recurrent premature births than whites, and are more likely to repeat delivery at a similar week of gestation as before.
The researchers say their analysis doesn't prove a genetic component to racial disparity in pre-term births but suggests a larger contribution than previously appreciated.
"These findings highlight the importance of race, particularly after correction for other risk factors, and suggest a probable genetic component that may underlie the public health problem presented by the racial disparity in pre-term birth," Muglia said.
Muglia said the study points to the need to increase surveillance of a pregnancy prior to the time a woman had an earlier pre-term delivery.
"It helps to clarify who's at risk, to monitor them more closely and intervene earlier," he said.
Ideally, additional research could offer insight on preventing pre-term deliveries, he said.
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