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.
