In a new study from a California community, women who had been pregnant at least four times were less likely to die from cardiovascular disease than those who'd never been pregnant.
Researchers said that could be due to the protective effects of pregnancy-related hormones as well as the extra social support that comes with having more children – or the fact that women who are able to get pregnant more often are healthier to begin with.
It's not clear that getting pregnant more often protects women's hearts, necessarily.
It's just one more little piece of the puzzle that maybe physicians should be aware of or think about, said coauthor Donna Kritz-Silverstein, from the University of California, San Diego.
Hypertension a likely cause of death
The new study, led by Marni Jacobs at UCSD, involved close to 1,300 women from Rancho Bernardo in Southern California. In the mid-1980s, when participants were in their early 70s, on average, researchers asked them how many times they had been pregnant and given birth. The women also answered questions about lifestyle habits related to heart health.
For the next 19 years, the researchers brought women in for regular clinic visits, sent them annual questionnaires and used death records to track their diagnoses.
Over that follow-up, 707 women, or about 55%, died of various causes. Just under half of those deaths were due to cardiovascular disease.
Compared to women who had never been pregnant, those who reported at least four pregnancies were about 35% less likely to die of cardiovascular disease, and they were half as likely to be killed by a stroke or another condition related to atherosclerosis or hypertension.
No link between pregnancy, death
The trend held up when the researchers looked specifically at the number of times women had given birth, and not just how often they'd been pregnant – but in that analysis, the lower risk of cardiovascular death that came with more kids wasn't statistically significant.
The authors noted online in Fertility and Sterility that only 131 women gave birth to four or more kids – 131 of them - whereas 240 had been pregnant at least four times in their study.
On the other end of the spectrum, 316 women said they had never been pregnant and 406 had never given birth.
There was no link between the number of times women were pregnant or gave birth and their chance of dying from all causes combined during the study.
More oestrogen in lots of pregnancies
The researchers said the findings may not apply to postmenopausal women in general, as the women in their study had especially long life spans, were relatively well-off financially and had good access to health care.
But they proposed a few explanations for the link between the number of times women had been pregnant and their chance of dying from cardiovascular disease. For example, women who are pregnant more times produce more oestrogen over the long run, and longer lifetime exposure to the hormone may have protective heart effects.
Alternatively, heart-related deaths could be reduced in women who have lots of grown children and social support around them as they age.
Higher fertility reflects better health
Finally, Kritz-Silverstein and her colleagues wrote that higher fertility may just reflect better general health – although their associations stood up when they took into account blood pressure and cholesterol readings as well as lifestyle habits.
It's really hard to tease out the cause, she said. We're just speculating – there's no real way that we can know that from our data.
Kritz-Silverstein added that future research into the link between pregnancy history and cardiovascular disease could help get at some of the differing heart risks and protective effects in men and women, including the not-so-obvious factors.
(Reuters Health, December 2011)