U.S. study suggests genetics may be the reason why
By Ed Edelson
HealthDay Reporter
FRIDAY, Feb. 9 (HealthDay News) -- Black women are three times more likely than white women to deliver their babies prematurely, a new study reveals.
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.
"What we would like to do is identify in a broad way the factors that increase the incidence of premature delivery," Muglia said. "We want to identify families and examine them for polymorphisms," genetic differences associated with an increased incidence of premature childbirth.
Muglia and his colleagues have been working with 75 families in the St. Louis area for the past three years, and have started a study of similar families in Finland. "We don't have data yet," he said. "It would take many subjects to pick out those genes."
One working hypothesis is that there might be some hidden evolutionary benefit to preterm delivery. "For maternal survival, it might be better to deliver early," Muglia theorized.
To support that notion he cited sickle cell anemia, a genetic condition more common in blacks than whites. Carriers of two genes for the condition are at a handicap, but it has been found that the presence of a single sickle cell gene protects the carrier against malaria, Muglia noted.
"I'm not sure it really gives us definitive answers," said Dr. Diane Ashton, deputy medical director of the March of Dimes. "But it is one aspect that the March of Dimes is looking at to assess the differences in premature births."
There have been hints of a genetic factor, Ashton added, citing a study indicating that black women were more susceptible to early rupture of the membranes.
"There is some evidence here, but this is one study, and until we have some reproducible results I don't think we can base our final opinion on just one study," she said.
A 2006 report by the U.S. Institute of Medicine found that 12.5 percent of American babies were born at least three weeks ahead of their full-term delivery date. Care for those babies costs the nation $26 billion a year, with some requiring neonatal intensive care for two weeks.
Potential problems for premature babies include hearing loss, vision loss, cerebral palsy and seizures. Such problems are most common in babies born before 32 weeks of pregnancy.
SOURCES: Louis J. Muglia, M.D., Ph.D, director, Washington University Center for Preterm Birth Research, St. Louis; Diane Ashton, M.D., deputy medical director, March of Dimes; February 2007 American Journal of Obstetrics and Gynecology
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