Moms, on some days you might feel as if life with children sends your blood pressure soaring, but a study released today suggests that having one healthy pregnancy actually lowers it, an effect that might last until your firstborn enters college or even beyond.
The researchers studied 2,304 women ages 18 to 30, about half of whom were black and half were white. They measured the women's blood pressure before and after their pregnancies and in follow-up visits, up to 20 years after their first measurement. Only women who did not develop high blood pressure while pregnant were considered in the analysis.
On average, the systolic blood pressure -- the top number -- in women who delivered one baby was 2 millimeters lower than that of women who never delivered a baby. The diastolic blood pressure -- the bottom number -- was 1.5 millimeters lower.
Blood pressure remained lower for years after delivery, although it did not continue to decline after subsequent pregnancies, the researchers write in the December issue of the journal Obstetrics & Gynecology. And the differences between the mothers and the women who had never delivered babies held, even after accounting for differences in factors that could contribute to high blood pressure, such as smoking and weight gain.
"The impact looks small on an individual level," says lead author Erica Gunderson, an epidemiologist with the Kaiser Permanente Division of Research in Oakland. "At a group level, it's an incredibly important impact."
Gunderson says she and her co-authors hypothesize that changes seen in early pregnancy, such as more flexible blood vessels, might persist long afterward. But, she says, their study doesn't prove it. Perhaps instead, Gunderson says, more of the women who had healthy pregnancies than those who didn't have babies were healthy to begin.
The study didn't take into account at least one factor that could influence blood pressure levels: salt intake, says co-author Gina Wei, the project officer for the study at the National Heart, Lung, and Blood Institute, which funded the research. Wei says the findings need to be replicated by other studies.
Besides a study published in 1997 that involved only 30 women, this is the first to examine whether pregnancy has a lasting influence on women's blood pressure, the authors write.
Not everything about pregnancy is necessarily good for women's health. Gunderson says her previous work suggests that pregnancy leaves women with lower levels of HDL, or good, cholesterol and bigger waistlines, both of which could increase the risk of diabetes, heart attack and stroke.
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