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Guidelines for managing blood pressure in pregnancy not consistent (2-13-01)

A study by researchers at The University of Texas Health Science Center at San Antonio (UTHSC) challenges current guidelines for the best management of mild chronic hypertension during pregnancy. The study was presented at the annual meeting of the North American Primary Care Research Group in Amelia Island, Fla.

Lead researcher Robert L. Ferrer, M.D., assistant professor in UTHSC’s Department of Family and Community Medicine, and his research team undertook an exhaustive review of the evidence, both quantitative and descriptive, to explore the foundation of treatment recommendations currently advocated in a diverse array of guidelines and review panels – including the national consensus guideline followed by most physicians in Canada.

Dr. Ferrer said guidelines from different specialty groups are not consistent. “The American College of Obstetrics and Gynecology saw this as one of the topics it would like to fund for systematic review, so that's how we ended up doing it."

The researchers undertook computer searches of 16 databases and also reviewed textbooks and more than 6,000 abstracts. They were primarily interested in material related to:

•risks of mild chronic hypertension (blood pressure of less than 160/110 mm Hg) to mother and fetus;

•benefits or harms associated with anti-hypertensives, aspirin and non-pharmacological treatments (such as weight reduction and exercise); and

• benefits or harms associated with monitoring strategies, such as ultrasound and amniocentesis, used to identify complications.

Two reviewers abstracted the trial data and another reviewer abstracted the epidemiological studies. Authors were contacted for critical design features or outcome data when such information was missing from published reports. Fetal and maternal risks associated with chronic hypertension in pregnancy were calculated.

The review focused on four main outcome measures: perinatal mortality, pre-eclampsia (a complication of pregnancy often marked by high blood pressure), birth weight and placental abruption.

It is the largest review of the data ever undertaken in this area, but the results could point only to the need to question current assumptions and proceed with population-based research.

Dr. Ferrer said the review left no clear evidence-based direction for doctors to follow in managing pregnant women with mild chronic hypertension.

"We've documented that the condition poses an increased risk to the fetus, but we don't know the extent to which medication lowers that risk," he said, adding that some evidence indicates, in certain instances, the medication in itself might be harmful, leading to low-birth-weight babies.

Dr. Ferrer said large, collaborative, multi-center studies enrolling thousands of women are needed if researchers are going to get a decent answer as to whether hypertension treatment has a significant effect on neonatal mortality from pre-eclampsia.

What should physicians say to their patients while a more soundly evidence-based set of guidelines is being developed? "Blood pressure of 160/110 mm Hg is the cutoff," Dr. Ferrer said. "Above that level there is general agreement regarding treatment interventions. For the borderline cases, we're probably in the gray zone.”

Contact: Will Sansom