A new study highlights the importance of knowing your cardiovascular risk factors and watching out for suspicious symptoms—even if you're young and healthy.

The risk of suffering a heart attack while pregnant, giving birth, or during the two months after delivery rose 25% between 2002 and 2014, according to a new study published in Mayo Clinic Proceedings. Study authors say the increased risk is alarming, especially since medical advances have improved the care of cardiovascular disease during this time.

First author Nathaniel Smilowitz, MD, an interventional cardiologist at NYU Langone Health, says his team’s decision to study this trend was based on episodes they’d witnessed in their own hospital as well as hospitals around the country.

“We’ve encountered women who come in during or after pregnancy with a heart attack, and it’s always unexpected and shocking for the woman who was otherwise healthy before this event,” Dr. Smilowitz tells Health. “There’s not a lot of literature out there on this topic, so we decided to take a look.”

Dr. Smilowitz and his team collected data from more than 55 million births that took place at hospitals in the United States over the 13-year study period. They found that 1,061 heart attacks happened during labor and delivery, while another 922 and 2,390 women were hospitalized for a heart attack before birth or during the recovery period after birth, respectively.

“Of those patients who were hospitalized, about one in 12,000 were for a myocardial infarction,” says Dr. Smilowitz. (A myocardial infarction is the technical term for a heart attack.) The overall rate of heart attacks during or after birth was low, he adds, “but it was not insignificant.”

The researchers also noted a 25% increase in heart attack rate over the study period—from 7.1 for every 100,000 pregnancies in 2002 to 9.5 for every 100,000 pregnancies in 2014. “Moreover, the patients who did develop a heart attack in the setting of pregnancy did not do well,” Dr. Smilowitz says. “About 4.5% died in the hospital, which is a very surprisingly high number.”

The mortality rate among pregnant women and new moms who suffered a heart attack remained unchanged over the study period, despite new advances in treating heart attacks, the authors say. These advances include drug-coated stents and improved use of blood-thinning medications to prevent blockages.

This study was not designed to determine why heart attack rates during and after pregnancy have increased, but the authors do have some suspicions. “Women are waiting longer to have children, and women who are pregnant are older today than they were a decade ago,” says Dr. Smilowitz.

Doctors know that a pregnant woman’s heart attack risk rises as her age increases, and the study’s data supported this notion: Women between the ages of 35 and 39 were five times more likely to suffer a heart attack than women in their 20s, for example, while women in their early 40s were 10 times more likely.

Rates of diabetes and obesity across the country have also increased over this time period, and both of these conditions are risk factors for heart attack too. But Dr. Smilowitz points out that 61% of the heart attacks in the study occurred in women who did not have known risk factors—and that more than half occurred in women younger than 35.

“Women who were young and otherwise healthy were still vulnerable, and that was surprising,” he says.

Finally, the study authors point out, diagnostic tests for heart attacks have also improved and become more widely available in the last decade—which could explain at least part of the jump.

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The study serves as a reminder of how stressful pregnancy can be on the body and the heart, the study authors say, and how important it is for women to talk with their doctors about their cardiovascular risk factors when they become pregnant, if not earlier.

“Women should be consulting with their physicians to manage their blood pressure, control their blood sugar, and reduce their cholesterol,” says Dr. Smilowitz. “Ideally that happens before a woman gets pregnant, but early on in a pregnancy can also help keep those risk factors under control.”

Women who are pregnant or who have recently given birth should also pay close attention to things like chest discomfort and burning and should seek medical attention if these symptoms do occur. “No young woman who is pregnant thinks of a heart attack as a complication,” says Dr. Smilowitz, “but this study shows us that ignoring these symptoms would obviously be the wrong move."