Ike S. Okwuosa, MD reports:

CHICAGO -  Heart attacks are often linked to high blood pressure, diabetes and smoking. But a new study suggests pregnancy can also increase the risk.

"There are significant hormonal changes that occur during pregnancy that affect the coronary arteries," said study author Dr. Uri Elkayam, professor of medicine, cardiology, and obstetrics and gynecology at the University of Southern California.

Those pregnancy-related hormonal changes,  Elkayam said, leave women "susceptible to clots."

Elkayam and colleagues reviewed 150 cases of heart attack during pregnancy between 2005 and 2011. They presented their findings today at the 61 st conference of the American College of Cardiology in Chicago.

Heart attacks are usually triggered by  atherosclerosis - a build-up of plaque that narrows the arteries and makes it harder for blood to flow.  But only a third of heart attacks that occur during pregnancy are caused by atherosclerosis, Elkayam said. Rather the vast majority are caused by a tear of one of the three layers that make up a blood vessel known as a dissection.

Seventy percent of spontaneous coronary dissections occur in women and 30 percent of those occur during pregnancy or immediately after, according to Dr. Sharonne Hayes, a cardiologist at the Mayo Clinic in Rochester, Minn. who was not involved in the study. "We have known for decades that young women with heart attack have higher mortality than men at the same age and also have very different cardiovascular disease risk factors," she said.

Heart attacks are usually treated with clot-busting drugs and balloons or stents that open up the narrowed artery. But for pregnant women with dissections, typical treatments can make the situation significantly worse.

Elkayam found that "performing a coronary angiogram, in which you inflate a balloon and place a stent, in 5 percent of the patients made things worse… In patients who are stable, we advise to evaluate the patient non-invasively, and only the high risk patient should undergo a cardiac catherization," he said.

A heart attack occurring in a young, previously healthy young woman is very unusual, with a reported incidence of 1/16,000. Elkayam emphasized that "women should not be afraid to become pregnant because the incidence of a heart attack is very small."

Dr. Okwuosa is an internal medicine resident Northwestern Memorial Hospital's Feinberg School of Medicine.