Scientists have a new clue about why preterm birth is more common among black women than white women.

A gene variation seen more often in people of African descent may be part of the reason, researchers write in this week’s early online edition of Proceedings of the National Academy of Sciences.

Researchers included Jerome Strauss III, MD, PhD, dean of Virginia Commonwealth University’s medical school.

“Our discovery of an association between a gene variation that is more common in individuals of African descent and a cause of premature birth can explain in part the disparity in prematurity rates in African Americans,” Strauss says in a Virginia Commonwealth University news release.

The finding may also help identify women at risk for preterm birth “so that appropriate monitoring and therapy can be applied in order to prevent this serious pregnancy complication,” Strauss says.

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Preterm Birth

In the U.S., black women have two to three times as many preterm births as white women, the researchers note.

Many factors may raise the risk of giving birth early, including:

--Smoking during pregnancy

--Past preterm deliveries

--Being pregnant with twins, triplets, or other multiples

--Vaginal bleeding in the second trimester (the fourth through sixth month)

--Infection in the urinary or reproductive tract, including the vagina

--Being younger than 18

--Low BMI (body mass index) in the pregnant woman

--Frequent contractions

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The black-white gap in preterm birth can’t be fully explained by either social and economic factors, or access to health care, write Strauss and colleagues.

So Strauss’ team looked for gene clues.

Gene Study

They focused on the SERPINH1 gene, which helps make collagen.

Collagen is a protein. It’s found in many parts of the body, including the membranes that hold the fetus in the womb.

One particular variation of the SERPINH1 gene leads to lower levels of collagen production, which might make preterm birth more likely, the researchers note.

Strauss’ team studied DNA samples from U.S. whites, Bolivians, Mexicans, Guatemalan Mayans, South Asian Indians, Chinese, Nigerians, and seven different ethnic groups from the African nation of Sierra Leone.

The SERPINH1 gene variant was most common among Africans, especially those from Sierra Leone, the study shows.

The researchers also checked the DNA of 323 black women and 148 white women who got obstetrical care at the Hospital of the University of Pennsylvania or at Detroit’s Hutzel Hospital.

The women accounted for 244 babies born to mothers whose water broke before 37 weeks of pregnancy, or before the baby was considered full term.

About 12 percent of the black women had the gene variant, compared to around 4 percent of the white women, the study shows.

The researchers don’t claim the gene variant makes preterm birth certain, and they’re not ruling out other risk factors.

However, the finding marks the first example of an ancestral genetic marker for preterm birth risk in black women, the researchers note.

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By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Wang, H. Proceedings of the National Academy of Sciences of the United States of America, week of Aug. 21-25, 2006; early online edition. News release, Virginia Commonwealth University. WebMD Medical Reference from Healthwise: “Preterm Labor: What Increases Your Risk.”