First Pregnancies May Permanently Lower Mom's Blood Pressure

Women may get an extra benefit form their first birth experience – lower blood pressure that endures long past delivery – according to a Kaiser Permanente study published this month.

The finding occurs in the December issue of Obstetrics and Gynecology.

"In women with healthy pregnancies, blood pressure levels were lower among women after a first pregnancy, compared to women who did not give birth," according to the study's lead author Erica P. Gunderson, Ph.D., an epidemiologist with the Kaiser Permanente Division of Research in Oakland, California. "Because lower blood pressure appears to persist years after delivery, pregnancy may offer insights into mechanisms that may be useful for controlling adult blood pressure."

Researchers examined blood pressure changes in 1,373 women who had never given birth at baseline. They found that the average systolic blood pressure was lower by 2 millimeters of mercury and the average diastolic blood pressure was lower by 1.5 mm of mercury for the 635 women who'd had a first pregnancy uncomplicated by hypertension, compared to 738 women who did not give birth during the 20-year study period.

The lower blood pressure was sustained regardless of the number of subsequent births, according to the researchers. Lower blood pressure after a first pregnancy compared with no births remained after adjusting for blood pressure and body mass index before pregnancy, age, race, smoking, education, medications to treat hypertension, oral contraceptive use, and weight gain, they explained.

A 2-mm mercury reduction in mean blood pressure for women's long term health could translate into a 6 percent reduction in stroke mortality, a 4 percent reduction in coronary heart disease, and a reduction in total mortality for 3 percent of the population, Gunderson said.

Although the biologic mechanism for blood pressure reduction is unclear, Gunderson explained that pregnancy may create enduring alterations in endothelial cells—the cells that line the blood vessels.

December 1, 2008 Kaiser Permanente News Center