In the study, published in the Feb. 22 issue of the British Medical Journal, researchers evaluated maternity data for nearly 130,000 women and then followed their records to see if they got heart disease.
Those who had had miscarriages were 1.4 times more likely to have heart disease later than women who had not. Moreover, those with repeated miscarriages were at even higher risk of heart disease -- women who had three or more were at more than double the risk of women who didn't have one.
"The main implication of the study is that there may be common determinants of heart disease and pregnancy complications," says study author Dr. Gordon C. S. Smith, a professor of obstetrics and gynecology at Cambridge University and the Rosie Hospital in Cambridge, U.K.
For instance, he says, certain antibodies [proteins produced by the body in response to "invaders" such as toxins] are associated with miscarriage as well as the risk of heart disease. "We do not think it is likely that the link is explained by the fact that these women already had heart disease at the time of their miscarriages," Smith says.
"We know from family history studies that there are genes which predispose toward heart disease," Smith says. "There are also other acquired factors which can predispose toward heart disease. Our interpretation of these findings is that these same factors may also determine pregnancy complications."
First, Smith and his team identified the 129,290 women eligible for the study who delivered their first live infant in Scotland during the years 1981-85. Nearly 12,000 had suffered a miscarriage or repeated miscarriages. Then, during 1981 to 1999, the researchers used hospital discharge and death data to determine the risk of death or hospital admission due to heart disease.
Any miscarriage that had occurred before the first live birth was associated with an increased risk of heart disease, regardless of a mother's age at birth, whether high blood pressure was present, or whether complications occurred during the first pregnancy. The more miscarriages, the higher the risk of heart disease.
If the current finding is replicated by further research, Smith says a woman's reproductive history might someday be incorporated into the assessment of her heart disease risk.
Another expert says the study is interesting and the topic deserves further investigation. "It makes sense biologically that people who have miscarriages would have an increased risk of cardiovascular disease later in life because many of the medical conditions that predispose people to have miscarriage can also predispose them to have heart disease," says Dr. Robert M. Silver, an associate professor of obstetrics and gynecology at the University of Utah School of Medicine.
Among those conditions, he adds, are kidney disease and a predisposition to blood clots. About 16 percent of pregnancies end in miscarriage, Silver says, and about 12 percent of those occur before week 12.
"The strength of the study is that it was [done] on a very large number of patients," he says. "One problem is that it's very superficial," he adds, adding the researchers did not control sufficiently for all the potential variables.
Women should not be alarmed, Silver says. "Most miscarriages are due to genetic problems with the pregnancy, not to underlying health problems of the mother," he says. "Most women who have miscarriages are not at increased risk for heart disease."