Possible Cause of Preeclampsia Uncovered
June 7, 2001 -- Even experts admit they're baffled about the cause of preeclampsia, a severe complication of pregnancy that causes high blood pressure and can threaten the life of both the expectant mother and her unborn child. But a new study suggests that the condition may be caused by the body's shortage of a natural compound that causes the blood vessel walls to relax.
Preeclampsia, which occurs in about 5% of all pregnancies, is a rapidly progressive condition marked by a sudden rise in blood pressure, abnormally high weight gain, severe headaches, vision problems, presence of protein in the urine, and buildup of fluid in tissues causing swelling. Because many of these symptoms can occur in a normal pregnancy, prompt evaluation and diagnosis by a physician, followed by prompt treatment when necessary, are essential to preserve the health of the mother and the fetus.
Since preeclampsia can be serious and sometimes fatal, women are often admitted to the hospital for bed rest and close monitoring. They may be treated with fluids and high blood pressure medications until the baby can be delivered safely, which usually resolves the condition.
"It's a major cause of maternal mortality, especially in developing countries where it may account for 80% of maternal deaths," says Valerian E. Kagan, PhD, professor of obstetrics and gynecology at the University of Pittsburgh, in an interview with WebMD.
Previous studies have suggested that preeclampsia is caused by poor blood flow to the placenta, the protective sack that supplies blood and nourishment to the developing fetus.
According to the new theory, which is described in the June issue of Circulation Research, this inadequate blood supply triggers oxidative stress, a condition in which oxygen compounds released into the bloodstream cause damage to tissues and interfere with the release of the chemical nitric oxide.
Normally, nitric oxide causes the walls of blood vessels to relax, thereby easing blood pressure. So a shortage of the chemical would lead to an increase in blood pressure.
This nitric oxide shortage theory is supported by a recent small study out of the U.K. This study suggests that vitamin C, an antioxidant, may reduce the incidence of preeclampsia because it prevents oxidative stress. Similarly, other evidence suggests that women who have low blood levels of ascorbate, a form of vitamin C found in the body, may be at increased risk for preeclampsia. Although the mechanism is unknown, ascorbate does play a role in the release of nitric oxide.
In the current study, Kagan and colleagues suggest that in pregnant women with preeclampsia, oxidative stress might cause a decrease in ascorbate levels. This decrease prevents nitric oxide from being released when needed, triggering a sharp rise in blood pressure and other symptoms.