Hypertension and uric acid contributes to premature delivery

Oct 30 2005

Pregnant women with hypertension who also have elevated blood uric acid levels may face an increased risk of complications that could be fatal for mother and baby, University of Pittsburgh researchers have found.

Reporting in the Oct. 27 online issue of Hypertension, a journal published by the American Heart Association, researchers note that the greatest risk of high blood pressure during pregnancy accompanies preeclampsia, a devastating disorder that affects some 5 percent of first pregnancies and is traditionally diagnosed by increased blood pressure and the presence of protein in the urine. The only effective treatment is immediate delivery, which, if too early, can pose risks to the fetus.

In developed countries where prenatal care is routine, preeclampsia accounts for about 15 percent of premature deliveries a year. Worldwide, in settings without good prenatal care, preeclampsia increases the risk of fetal death five-fold and kills 50,000 women a year, researchers said. For clinicians, treating preeclampsia is a delicate balance of fetal and maternal risk from the disease and fetal development-associated risk because of premature delivery.

"We used a research database to ask whether inclusion of uric acid levels in the diagnosis of preeclampsia would help us to evaluate risk for complications among patients," said James M. Roberts, M.D., professor and vice chair of research in the department of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh School of Medicine and the study's first author. "We focused primarily on fetal outcomes such as gestational age at delivery and birth weight, but also looked at markers of maternal disease, including severely elevated blood pressure during labor."

Records for 972 pregnant women who were recruited between 1997 and 2002 as part of an ongoing preeclampsia study at the Magee-Womens Hospital of the University of Pittsburgh Medical Center were reviewed and the women were divided into eight groups:

1. 431 women had normal levels of uric acid and blood pressure and no evidence of protein in their urine
2. 48 women had classic preeclampsia including high blood pressure and protein in their urine but normal uric acid
3. 141 women had preeclampsia and elevated levels of uric acid in their blood
4. 52 women had high blood pressure and elevated levels of uric acid but no protein in their urine
5. 184 women had only increased uric acid levels
6. 83 women had only high blood pressure
7. 21 women had only protein in their urine
8. 12 women had protein in their urine and elevated levels of uric acid but normal blood pressure

Analysis of the data revealed that the women with both preeclampsia and elevated uric acid levels had a nearly seven-fold increased risk of premature delivery and delivered nearly four weeks earlier than preeclamptic women whose uric acid levels were normal. Most of these deliveries were induced to prevent more severe maternal illness and infants tended to be smaller at birth, even adjusted for gestational age, Dr. Roberts said.

One of the more interesting findings was that for women with high blood pressure and no protein in their urine but who did have increased uric acid, the risk of early delivery or reduced fetal growth was at least as likely as in women with classic signs of preeclampsia but normal uric acid. Also, women with high blood pressure who lacked urine protein and had normal uric acid had no increased risk for babies.

"Irrespective of protein levels, women with high blood pressure had a higher incidence of being delivered early as uric acid increased," said Dr. Roberts, who also is director of the university-affiliated Magee-Womens Research Institute. "For every one-unit increase in uric acid, the odds of preterm birth increased 2.3 times."

While results of the National Institutes of Health-funded study seem to suggest that uric acid measures could have a utility for predicting risk of adverse outcomes, further prospective testing is necessary to confirm the findings and determine cost-effectiveness of its use to improve outcomes, Dr. Roberts said.

In addition to Dr. Roberts, other authors are Lisa M. Bodnar, R.D., Ph.D., Kristine Yoder Lain, M.D., M.P.H., Carl A. Hubel, Ph.D., Nina Markovic, Ph.D., Roberta B. Ness, M.D., M.P.H., and Robert W. Powers, Ph.D., all of the University of Pittsburgh School of Medicine.