African-American women are three times more likely to deliver babies three to 17 weeks prematurely than Caucasian women, according to a review of Missouri birth statistics by researchers at Washington University School of Medicine in St. Louis.

In addition, African-American women are more likely to deliver babies prematurely in subsequent pregnancies.

The researchers analyzed data from the Missouri Department of Health’s maternally linked database of all births in Missouri between 1989 and 1997, adjusting for such variables as socioeconomic status, education level, cigarette smoking and maternal medical conditions such as diabetes, hypertension and eclampsia. Full-term birth is considered to be between 37 weeks and 42 weeks of gestation.

Results of the analysis appear in the February issue of the American Journal of Obstetrics and Gynecology.

The data showed that 8.8 percent of births to African-American women were between 20 weeks and 34 weeks gestation, or nearly three times the 2.95 percent of premature births to Caucasian women. In addition, African-American women were nearly four times as likely to deliver babies between 20 weeks and 28 weeks gestation than Caucasian women.

African-American women also were nearly 5.5 times more likely to have recurrent preterm births than Caucasian women.

Nationally, Caucasian women have about an 11 percent risk of delivering prematurely, while African-American women have a 19 percent risk of delivering prematurely, said Louis J. Muglia, M.D., Ph.D., senior author and professor of pediatrics and of obstetrics and gynecology at Washington University School of Medicine.

“We found that African-American women experience preterm birth not only at increased rates as compared with Caucasian women but also at earlier gestations and with increased repetition for a woman who has had at least two babies,” said Muglia, director of the Center for Preterm Birth Research at the School of Medicine. “We also found that subsequent preterm births to a mother happen at the same week as her original preterm birth. 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 preterm birth.”

The genes likely involved in pregnancy and the birth process also impact other aspects of human health, said Muglia, director of the division of pediatric endocrinology and diabetes at St. Louis Children’s Hospital. So far, researchers have found a link between genes that play a role in human birth and those that determine the response to infection, but they are still working to pinpoint causes of preterm birth.

“By understanding specifically what results in this health disparity in African-American women, we can gain a tremendous amount of insight into a normal birth process in respect to preterm birth,” said Muglia. “If we can work to reduce the frequency of preterm birth in the African-American population, which is almost twice as great as in the Caucasian population, I think we will make an enormous impact on human health.”

Although other researchers have studied this phenomenon, this analysis further clarifies the risk of premature birth in African-American women and the probable genetic link.

“This study helps set the stage for identification of novel genomic strategies to understand fundamental mechanisms responsible for the epidemic of prematurity in the United States,” said F. Sessions Cole, M.D., assistant vice chancellor for children’s health at the School of Medicine and director of the Division of Pediatric Newborn Medicine and chief medical officer at St. Louis Children’s Hospital.