Black women may be genetically predisposed to giving birth prematurely, according to a new study from Washington University//.
The research is an important first step toward identifying women at risk for delivering babies too early and eventually could lead to treatments.
Researchers at the university examined 711,015 records of births between 1989 and 1997 kept by the Missouri Department of Health and Senior Services. The data showed that African-American women were nearly three times more likely than white women to have a baby prematurely.
Scientists have known there is a racial disparity, but they debate its cause. The Washington University researchers, led by Dr. Louis J. Muglia, wanted to find out whether genetics played a role. Previous studies have hinted that genetic factors might be important, but none has shown proof, Muglia said. He directs the new Center for Preterm Birth Research at Washington University.
His group decided to look at women for whom genetics was most likely to play a role — women who had more than one baby prematurely. Having one baby prematurely is the greatest risk factor for having another preterm birth. That's true for all women.
But the study showed that black women are at even higher risk of having more than one preterm baby. The rate of recurring preterm births for African-American women was 21.5 percent, in whites 9.2 percent. Even after adjusting for variables such as social and economic status, education levels, smoking and maternal medical problems, including diabetes and high blood pressure, black women were still four times more likely to have recurrent preterm births.
The black women also delivered two weeks earlier than white women with multiple preterm babies. The black mothers gave birth, on average, at 31 weeks gestation, while white moms averaged 33 weeks gestation.
Preterm birth is usually defined as delivery at less than 37 weeks of gestation. Th
e new study used 34 weeks gestation as a cut-off to avoid any errors in calculating the due date. The researchers considered 37 weeks gestation to 42 weeks full-term.
The study appears today in the American Journal of Obstetrics and Gynecology. The March of Dimes funded the study.
The data also revealed that a woman who had multiple preterm births tended to deliver at about the same stage in each pregnancy. Almost half of the mothers in the study had their babies within two weeks of the gestation time of their first premature child. It is unlikely that infections or other environmental factors would trigger premature births during such a narrow window, said Dr. Michael P. Nageotte, the immediate past president of the Society for Maternal-Fetal Medicine.
That clustering raises the possibility that a genetic clock controls the timing of birth and gets turned on too early in some women, Nageotte said.
The researchers concluded that genetics are the underlying reason for premature births.
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