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Press Release

November 25, 2008

Oakland, Calif. - Women may get an extra benefit from their first birth experience – lower blood pressure that endures long past delivery, according to Kaiser Permanente researchers.

The finding appears in the current online version 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, PhD, an epidemiologist with the Kaiser Permanente Division of Research in Oakland CA. “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.”

The researchers examined changes in blood pressure before and after pregnancy relative to women who did not give birth. They looked at a large, population-based, cohort of women of reproductive age (18-30 years) from the Coronary Artery Risk Development in Young Adults (CARDIA) Study.

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 2mm 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% reduction in stroke mortality, a 4% reduction in coronary heart disease, and a reduction in total mortality for 3% of the population, according to the researchers.

The researchers utilized standardized research methods to measure blood pressure before and after pregnancy.They examined changes in blood pressure among women who gave birth versus women who did not give birth, allowing them to examine blood pressure changes specifically related to pregnancy. Standardized blood pressure measurements were available before conception and after deliveries for all the women in the analysis and 89% or the sample had at least four measurements after baseline for up to 20 years later. Researchers also excluded women with hypertension at baseline, removed women with pregnancies complicated with hypertension from the analysis, and controlled for treatment of hypertension and weight gain during follow up.

Limitations of the study include variable timing of blood pressure measurements before conception and after delivery, and lack of blood pressure measurements during pregnancy. Self-report of hypertensive medication use outside of pregnancy is also a limitation, although this variable was controlled in the analysis.  It’s also possible that passage through the stress of pregnancy without hypertension may simply define a group of women who have healthier vascular function to begin with.

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

Funding for this study was provided by the National Heart, Lung and Blood Institute. Additional authors on the study include: Vicky Chiang, MS, Kaiser Permanente; Core E. Lewis, MD, MSPH, Division of Preventive Medicine, University of Alabama at Birmingham; Janet Catov, PhD, Department of Obstetrics and Gynecology, Magee-Women’s Hospital, University of Pittsburgh; Charles Quesenberry, Jr., PhD, Kaiser Permanente Division of Research; Stephen Sidney, MD, MPH, Kaiser Permanente Division of Research; Gina S. Wei, MD, MPH Division of Prevention and Population Sciences, National Heart, Lung, and Blood Institute, Bethesda, Maryland; and Roberta Ness, MD, MPH, Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh.