The use of fertility drugs is known to be associated with higher rates of such complications as high blood pressure and gestational diabetes during pregnancy, and researchers wanted to determine if related cardiovascular disease risks persist as women age.
"The speculated association between fertility therapy and subsequent cardiovascular disease is not surprising given that more women are waiting until an older age to have children, when they are at greater risk of developing heart disease," said Dr. Jacob Udell, a cardiologist at Women's College Hospital in Toronto who led the study.
Using a large Ontario health-records database, Udell and researchers at the Institute for Clinical Evaluative Sciences (ICES) compared women who used fertility drugs and those who conceived and gave birth without the therapy.
In all, the 1993-2010 study looked at data on more than one million women, whose health outcomes were followed for 10 years on average. Researchers looked at the incidence of heart attacks, strokes, heart failure, blood clots and death among the two groups.
The mean age of women overall in the study was 29, but among those taking treatment for infertility, the average age was 34 to 35, said Udell, noting that the use of the drugs rose five-fold during the study period, reflecting a societal shift in which more and more women have chosen to delay starting a family.
"We wanted to see whether (fertility drugs) had long-lasting effects," said Udell, whose work as a cardiologist includes caring for women with cardiovascular complications during pregnancy.
"And surprisingly, we found the opposite, that those who used fertility therapy had a lower risk of major cardiovascular events," said Udell.
"So they actually had a lower risk. And they had a lower risk of death and particularly of pulmonary embolism or DVTs (deep vein thrombosis)" — two types of potentially fatal blood clots, another possible complication while women are taking fertility drugs.
The study, published Wednesday in the Journal of the American College of Cardiology, found that women who gave birth following fertility therapy had nearly half the risk of such events as stroke, heart attack and heart failure, compared to women who did not have treatment.
Women who took the drugs also had comparatively about half the risk of subsequent death.
However, the researchers don't believe the lower risks result from the treatment; instead, they suggest women who have infertility therapy likely maintain a healthy lifestyle over a long period of time.
"Those with successful outcomes may have a powerful and durable change to their lifestyle," said study co-author Dr. Donald Redelmeier, a senior scientist at ICES. "Unknown protective mechanisms may also contribute."
The study also found:
—The use of fertility drugs was associated with an increase in pregnancy complications, including a nearly 30 per cent jump in gestational diabetes, a 16 per cent rise in placental disorders and a 10 per cent increase in pre-eclampsia.
—There was no increase in the risk of future breast or ovarian cancer in women who used fertility therapy.
—Women treatment for infertility also had fewer mental health issues, including about one-third the rate of depression and one-sixth the rate of self-harm.
"It should reassure folks, both the treating physicians and the patients, that there are no obviously long-term toxicities from these drugs," said Udell.
"But I think it does, I hope, bring attention to the fact that these women do have many risk factors going into fertility therapy. They are at least five years on average older compared to the general population and there are cardiovascular risk factors because as we age we accrue those."
Udell said more research is needed, and the team is planning a follow-up study that will look at women who used the therapy to see who got pregnant and gave birth compared to those unable to achieve a successful delivery.
He suggests women who have taken fertility drugs, especially if they have experienced elevated blood pressure or another pregnancy-related disorder, should be monitored for cardiovascular disease following delivery by an appropriate specialist.
"As an obstetrician, they're not going to be taking care of these women long-term, in terms of those risks, so they may kind of fall off the medical health radar for several years while they're caring for their new children," he said.
"So I'm advocating that these women, if they have risk factors for heart disease, get continued followup and be seen by their general practitioner or internist or cardiologist."