(Agencies)
Updated: 2007-09-14 03:27

NEW YORK - Obese pregnant women may have an increased risk of losing their baby relatively late in pregnancy, and black women appear particularly at risk, a large study suggests.

Researchers found that obese women were 40 percent more likely than normal-weight and overweight women to have their pregnancy end in stillbirth -- defined as fetal death in the 20th week of pregnancy or later.

African-American women were especially at risk. Compared with obese white women, their rate of stillbirth was 90 percent higher, the study authors report in the journal Obstetrics & Gynecology.

Part of the reason for the obesity-stillbirth link may rest in the fact that obese women are more prone to diabetes and high blood pressure in pregnancy, explained Dr. Hamisu Salihu, an associate professor at the University of South Florida in Tampa and the study's lead author.

Because black women have higher rates of these pregnancy complications than white women do, this may also help explain the racial gap, according to the researchers.

However, diabetes and high blood pressure are not the whole story, Salihu told Reuters Health, and other factors must be at work.

For example, he explained, obese women also have higher levels of lipids -- blood fats such as cholesterol. These fats suppress a substance called prostacyclin, which can narrow the blood vessels and promote blood clotting in vessels supplying the fetus.

Whatever the reason for the higher risk of stillbirth, the best way to reduce these odds is for obese women to shed weight before getting pregnant, according to Salihu.

"Weight reduction before becoming pregnant should be the cornerstone of any strategy that aims to reduce the high level of risk for stillbirth among obese mothers," he said.

The findings are based on pregnancy outcomes of more than 1.5 million Missouri women who were pregnant between 1978 and 1997. Salihu's team found not only that obesity raised the risk of stillbirth, but also that the odds continued to climb with the degree of obesity.

Women who were classified as extremely obese had nearly double the risk of stillbirth as women who were normal-weight or overweight before becoming pregnant.

While weight loss before pregnancy may be the best way to prevent these stillbirths, this is clearly not possible for all women. According to Salihu, researchers still need to determine the best way to manage obese women's pregnancies in order to lower the risk of stillbirth.

Obesity itself has only recently been recognized as a risk factor for stillbirth, he noted, and there are no standard recommendations on how doctors should address the problem.