Women who carry extra pounds before they get pregnant are more likely to develop preeclampsia, a high blood pressure condition that is a leading cause of maternal death.

Researchers at Magee-Womens Research Institute found that a woman with a pre-pregnancy body mass index, or BMI, of 26 was twice as likely to develop preeclampsia as a woman whose BMI was 21.

A 5-foot, 6-inch woman who weighs 160 pounds would have a BMI of 26, which is considered overweight. A woman of the same height who weighed 130 pounds has a BMI of 21, which is normal.

Investigator Lisa Bodnar, who works in the lab of renowned preeclampsia expert Dr. James Roberts, presented the findings this week in Washington, D.C. at the annual meeting of the American Society for Nutritional Sciences.

"There's so much about preeclampsia that's unknown," Bodnar said. "This is actually an attractive factor to look at because of the fact that BMI is modifiable, unlike many of the others."

Preeclampsia occurs in about 7 percent of first pregnancies nationally. Delivery of the baby is the only treatment. Elevated blood pressure and protein in the urine, the hallmarks of the disease, usually appear by about the fifth month of pregnancy.

"It increases [a woman's] risk of having hyptertension in a subsequent pregnancy and her risk of cardiovascular disease in the future," Bodnar explained. "[Babies] are more likely to be born early and too small."

Almost 1,200 women who were 16 weeks or fewer along in their first pregnancies joined the study. Researchers calculated their BMIs from their heights and pre-pregnancy weights and followed them until delivery.

They found that 6 percent of participants developed preeclampsia, and that higher BMIs led to a greater risk. Women who were underweight with a BMI of 17 were half as likely to get the condition than those who had a BMI of 21.

Bodnar cautioned that pregnant women should not attempt to lose weight without talking with their doctors. Weight gains during pregnancy did not influence preeclampsia rates in the study.

The researchers plan to examine why an elevated BMI, which could be accompanied by high lipid levels, predisposes women for the condition.

Obesity is on the rise nationally, so doctors might see parallel increases in preeclampsia and gestational diabetes, Bodnar noted.

"We really don't know enough about the reproductive consequences of obesity," she said. "It's an area that's really been neglected and we should pay more attention to it because it's clearly going to be an increasing problem."