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Heart attacks in pregnant women are rare, but the number is rising, particularly among older expectant mothers, according to a new study that looked at the most common factors behind the increase.

The number of women who had heart attacks during or after pregnancy rose 19 percent from 2005 to 2014, the study found.

"We want doctors to maintain a high index of suspicion for this rare but (potentially) deadly event," said the study's lead researcher Dr. Byomesh Tripathi of St. Francis Hospital and Medical Center in Hartford, Connecticut. The findings will be presented Saturday at the ·¬ÇÑÊÓƵ's Scientific Sessions conference.

"Because pregnant women are young, when they get chest pains, cardiologists don't suspect a heart attack right away because they typically don't have conventional risk factors," he said.

Researchers analyzed more than 43 million pregnancy-related hospitalizations from a national database and found 3,786 cases of heart attacks. Overall, about 8.7 heart attacks occurred per 100,000 women hospitalized during or after pregnancy. The rate fluctuated over the years but peaked at 10.3 heart attacks per 100,000 women in 2011.

The most common predictors turned out to be age, race and whether the woman had other chronic illnesses such as high blood pressure, diabetes or high cholesterol.

Pregnant women 40 or older had a 10-fold higher risk of heart attack, something researchers found troubling given that more women are having children later in life.

They also found that black women were about 60 percent more likely than white women to have heart attacks, primarily because of socioeconomic factors such as poor insurance coverage, lack of quality care and insufficient prenatal counseling.

Other top predictors included congestive heart failure, anemia and pregnancy-related complications such as preeclampsia, gestational high blood pressure and an imbalance of fluids and electrolytes.

Although heart attacks among pregnant women are uncommon, the numbers still warrant attention, said Dr. Afshan Hameed, a cardiologist and high-risk obstetrician who was not associated with the study.

"Even if you take an otherwise healthy 20-year-old woman, the risk is way higher in pregnancy even if she may not have underlying risk factors. It's just from the stress of pregnancy," Hameed said.

"It may be the hormones, it may be the high (blood) volume that pregnancy causes to circulate in the woman's system. The blood vessels in pregnancy become more fragile, so they are more prone to be damaged from any risk factors."

That's also why pregnant women are more likely to have different types of heart attacks, said Hameed, a professor of cardiology and obstetrics and gynecology at the University of California, Irvine.

Most heart attacks are caused by a fatty buildup inside the inner walls of coronary arteries that blocks blood flow. But for pregnant women, a common cause is a tear in the lining of a coronary blood vessel, something considered rare in non-pregnant patients.

Hameed said the study should heighten awareness among both doctors and patients, since women tend to wave away troubling symptoms. For example, pregnant women may dismiss one particularly common heart attack sign as heartburn.

"But if they're having chest pain, it could actually be a red flag for them to go see a doctor," she said.

"The biggest gap in the care of pregnant women with heart disease is that we don't put two and two together," she said. "These are the things that need to be conveyed to the general public."

Find more news from Scientific Sessions.

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