Nearly 5 percent of pregnant women are prescribed drugs to treat high blood pressure , including some drugs that aren't considered safe for mothers or their babies, according to new research in the American Heart Association's journal Hypertension.

Use of high blood pressure drugs during pregnancy is becoming increasingly common, said Brian T. Bateman, M.D., lead author and Assistant Professor of anesthesia at Harvard Medical School in Boston, Mass.

"While we know high blood pressure, or hypertension, occurs in about 6 percent to 8 percent of all pregnancies, we know little about how women and their doctors treat the condition," he said.

Researchers studied a database of more than 1 million Medicaid patients, of whom 48,453 (4.4 percent) filled prescriptions for high blood pressure drugs during their pregnancies.

They found:

    Antihypertensive drug use increased from 3.5 percent to 4.9 percent between 2000 and 2006.
    Antihypertensive drug users were older than non-users, more likely to have diabetes or kidney disease, and more likely to be Caucasian or African-American than Hispanic or Asian.
    Nearly 2 percent of pregnant women filled prescriptions for these drugs during the first trimester; 1.7 percent during the second trimester; and 3.2 percent during the third trimester.
    The drugs prescribed included ACE inhibitors and angiotensin receptor blockers -- both of which have been shown in studies to have harmful side effects during pregnancy.

Limited information is available about which antihypertensive drugs are safest and most effective for treating high blood pressure during pregnancy, Bateman said. In general, methyldopa and labetalol are the recommended antihypertensives for use during pregnancy. More research on which antihypertensives to prescribe during pregnancy and how to use them safely is urgently needed, he said.

"We know from reports that a number of harmful effects can occur from using ACE inhibitors or angiotensin receptor blockers, especially during the second and third trimester," Bateman said. "These drugs can cause poor growth, kidney problems and even death of the newborn. If women are taking one of these blood pressure medications and they become pregnant or plan to do so, they and their doctors should discuss treatment choices during pregnancy."

Co-authors are Sonia Hernandez-Diaz, M.D., Dr.P.H.; Krista F. Huybrechts, M.S., Ph.D.; Kristin Palmsten, M.S.; Helen Mogun, M.S.; Jeffrey L. Ecker, M.D. and Michael A. Fischer, M.D., M.S. Author disclosures are on the manuscript.