Women with more than three spontaneous miscarriages were over five times more likely to suffer a heart attack later in life after adjusting for other factors, according to Dr. Elham Kharazmi of the German Cancer Research Center in Heidelberg, Germany, and colleagues.
Induced abortion, though, appeared to have no link to heart attack risk, the group reported online in Heart.
The link between recurrent pregnancy loss and cardiovascular disease may lie in common risk factors, perhaps because of the role of vascular health in placental function, they suggested.
"Recurrent miscarriage and stillbirth ... should be considered as important indicators for monitoring cardiovascular risk factors and preventive measures," they wrote.
Traditional risk factor analysis underestimates women's risk for heart disease, Suzanne Steinbaum, DO, of Lenox Hill Hospital in New York City and an American Heart Association spokesperson, noted in a statement sent to reporters.
"When evaluating a woman's risk for heart disease, her risks cannot be defined the same as a man," she wrote. "The data seen in this trial demonstrates that the obstetrical history of a woman, including miscarriages and stillbirths, must be factored into the risk analysis to determine each individual woman's risk for heart disease."
Given conflicting prior studies, Kharazmi's group analyzed data from the European Prospective Investigation into Cancer and Nutrition cohort in Heidelberg.
Although this prospective population-based study had been designed to look at the association between diet, lifestyle, and chronic diseases, it also collected data on women's reproductive history.
The analysis indicated that of the 11,518 women ages 35 to 66 in the study who had ever been pregnant, 25 percent had had at least one miscarriage, 18 percent had had at least one abortion, and 2 percent had had at least one stillbirth.
During the mean follow-up of 10.8 years in the study, 79 of the women who had been pregnant had a first heart attack.
Overall, age-adjusted heart attack risk appeared to rise significantly -- by 42 percent -- with each miscarriage for a 4.34-fold greater risk among those with two or more miscarriages compared with those who had none.
Stillbirth was tied to a 3.7 times higher risk of heart attack, which remained significant after full adjustment for smoking, body mass index, physical activity, hypertension, number of pregnancies and other factors.
No type of pregnancy loss was significantly linked to risk of stroke, but the researchers cautioned that these results were inconclusive because of the wide confidence intervals.
They also cautioned that residual confounding may have been possible and that follow-up may not have been long enough for the younger women in the cohort to have been in an age range when heart attacks would be more likely to be seen.
Under-reporting of miscarriages was likely since women in some cases don't even realize that they have been pregnant before its loss, Kharazmi's group noted.
Further research is needed to determine what underlying risk factors link pregnancy loss and cardiovascular disease, the researchers noted.