Blood test for predicting pregnancy problems. (Preeclampsia Progress).

A natural compound that constricts blood vessels is overabundant in some women who develop preeclampsia or another late-term complication of pregnancy, researchers find. Testing for the substance might help doctors identify some women at risk for preeclampsia before they develop high blood pressure and other symptoms. The findings also hint that the compound may play a role in causing the perplexing condition, as may a protein identified earlier this year (SN: 3/8/03, p. 147).

The focus of the new work, the substance called asymmetric dimethylarginine (ADMA), works by inhibiting production of a blood vessel dilator, nitric oxide. Vessels in the uterus must dilate to supply a fetus with adequate oxygen and nourishment.

Doctors usually detect preeclampsia by noting a rise in a pregnant woman's blood pressure, coupled with swelling of her face, hands, and feet and a buildup of protein in the urine. In the most serious cases, preeclampsia leads to eclampsia, which is marked by high fever, convulsions, and coma. Eclampsia causes at least 50,000 maternal deaths each year worldwide.

Suspecting a link between the high blood pressure of preeclampsia and ADMA, Kypros H. Nicolaides of Kings College Hospital in London and his colleagues collected blood samples from women midway through uncomplicated pregnancies.

Using ultrasound, the doctors also measured blood flow in each woman's arm as a gauge of vessel constriction throughout the body. The researchers considered this measurement a proxy for blood flow to the placenta, the interface between mother and fetus. Out of the group tested, the scientists selected 43 women who had normal blood flow and 43 others with restricted flow.

Tests of the blood samples showed that ADMA concentrations were, on average, three times as high in the women with restricted blood flow as in the others.

All of the women with normal blood flow went on to have healthy pregnancies and births. Of the others, slightly more than half encountered complications. Ten of the 43 women with restricted blood flow were later diagnosed with preeclampsia, and 14 others developed a complication called intrauterine growth restriction, in which the fetus remains undersized.

In the 10 women who later developed preeclampsia, the amounts of ADMA in their blood samples correlated with greater constriction of the women's blood vessels, but the relationship was less clear in the others with restricted flow.

The researchers note that the high concentrations of ADMA showed up roughly 10 weeks before preeclampsia, suggesting that high ADMA might be an early warning sign or even a cause of the condition. They report their findings in the May 3 Lancet.

The combination of a blood-flow test and ADMA measurement might better predict preeclampsia than either would alone, says Anthony R. Gregg of the Baylor College of Medicine in Houston. "Anytime we can find a clinical marker for preeclampsia that really predates [the disease], it's significant," he says.

At present, the only cure for preeclampsia is for a woman to give birth, although bed rest, blood pressure control, and anti-seizure drugs can extend a pregnancy (SN: 6/22/02, p. 398). Such treatment for a woman known to be at high risk for preeclampsia "might buy a little more time" before a baby has to be delivered, Gregg says.

The research also contributes to scientists' understanding of uterine blood flow and pregnancy complications, says John T. Repke of Penn State College of Medicine in Hershey, Pa. To that end, other researchers are investigating whether a deficiency in nitric oxide made by vessel-lining cells triggers pregnancy problems.

STATS

1 in 20 pregnancies is complicated by preeclampsia