Even worse, they are four times more likely to give birth extremely prematurely — between 20 to 28 weeks gestation.
Genetics are the most likely reason for the phenomenon, the study’s lead researcher said.
“It has been known that African-American women have an increased risk of preterm delivery,” said Dr. Louis J. Muglia, director of the Center for Preterm Birth Research at Washington University School of Medicine, in St. Louis. “By this study we are trying to understand the foundation for that effect.”
His team published its findings in the February issue of the American Journal of Obstetrics and Gynecology.
The study tracked more than 700,000 births in Missouri from 1989 to 1997.
The researchers found that black women were three times more likely than their white counterparts to give birth at 20 to 34 weeks of pregnancy, rather than full-term (from 37 to 41 weeks).
The researchers controlled for socioeconomic factors, such as maternal age and economic status, Muglia said. Without adjusting for those factors, “the incidence of premature delivery would be 6.5-fold higher than in Caucasians,” he noted.
In addition, 21.5 percent of the black women in the study had more than one premature delivery, compared to 9.2 percent of white women, the study found.
While there is no direct proof that genetic differences drive the disparity, the evidence does point in that direction, Muglia said. His group now is engaged in studies to try to prove that notion, he added.