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The number of women who experience heart attacks while pregnant, giving birth, or during the two months following birth is on the rise.

A study from the New York University School of Medicine found the risk for suffering a heart attack among pregnant and recently pregnant women rose by 25 percent between 2002 and 2014.

The researchers studied over 49 million births recorded in hospitals. They found that 1,061 heart attacks occurred during labor and delivery, 922 women were hospitalized prior to birth due to heart attacks, and 2,390 heart attacks occurred during the two-month recovery period following birth.

Heart attack rates were also shown to have increased from 7.1 out of every 100,000 pregnancies in 2002 to 9.5 out of every 100,000 pregnancies in 2014.

“Heart attacks occur in 1 out of every 12,000 hospitalizations during or immediately following pregnancy. In addition, 1 out of every 20 women who had a heart attack during pregnancy died during their hospital stay,” Dr. Nathaniel Smilowitz, an interventional cardiologist and assistant professor medicine at NYU Langone Health, and lead author of the study, told Healthline. “Although heart attacks in young women are rare, the time during and immediately after pregnancy is a particularly vulnerable period during which heart disease may be unmasked.”

He added, “In light of overall improvements in cardiovascular disease prevention and treatment during the time period we studied, the 25 percent increase in heart attacks during pregnancy was a surprising finding.”

Heart disease is the leading cause of death for most ethnicities in the United States

According to the Centers for Disease Control and Prevention, heart disease is second only to cancer as the leading cause of death for Native Americans, Alaskan Natives, Asians, and Pacific Islanders. Annually, approximately 735,000 Americans have a heart attack. Of those, 525,000 are first attacks, and 210,000 occur in those who’ve already had a heart attack.

High cholesterol, high blood pressure, and smoking are main risk factors for a heart attack and 47 percent of Americans have at least one risk factor.

Why are more pregnant women having heart attacks?

The researchers from NYU say the increase in heart attack rates among pregnant or recently pregnant women could be due to the fact that many women are choosing to have children later in life.

A woman aged between 35 to 39 is five times more likely to have a heart attack while pregnant than a woman in her 20s. A woman in her early 40s is 10 times more likely to have a heart attack than a woman in her 20s.

“Pregnancy and childbirth is the first true metabolic stress test, and it could unmask underlying cardiovascular disease. With older women — especially those with risk factors — this might not just be revealed with issues like high blood pressure or elevated sugars, but could be manifested with an actual heart attack,” Dr. Suzanne Steinbaum, director of Women’s Cardiovascular Prevention, Health and Wellness at Mt. Sinai Heart, told Healthline.

Lifestyle factors may also be contributing to higher rates of obesity and diabetes, which are known risk factors for heart attacks.

“Heart disease is 80 percent preventable through lifestyle intervention. During pregnancy and childbirth, although this risk may go up for some women, the reasons it happens is the same for all,” Steinbaum said. “Managing your risk factors with maintaining a healthy lifestyle is critical. Knowing your numbers and getting them to goal can be the most lifesaving strategy for yourself not only during pregnancy and childbirth, but throughout your life.”

It can happen to healthy pregnant women as well

The researchers found that women who had risk factors were at the highest risk of heart attack. However, it’s also possible for heart attacks to occur in otherwise healthy women.

“Of those who had a heart attack during or immediately after pregnancy in this study, the majority of women did not have known risk factors for heart disease,” Smilowitz said.

Although heart attacks in young women are considered rare, the relatively high death rate has remained the same despite advances in medicine including blood thinning medications and treatments like drug-coated stents.

“Among women who developed a heart attack during or immediately following pregnancy, the in-hospital mortality rate was 4.5 percent, a figure that’s surprisingly high considering that this is an otherwise low-risk population of young women of childbearing age,” Smilowitz said.

During pregnancy, there’s an increase in maternal blood volume, cardiac output, and heart rate. The arteries dilate to accommodate the growing fetus and need to be healthy to allow this dilation to occur as the pregnancy demands. Underlying risk factors can impair the ability of arteries to dilate. This, coupled with an increased heart rate, a cardiac output 40 to 50 percent higher than normal, and the added weight from the fetus, can put additional stress on the heart during pregnancy.

Dr. Katherine Bianco, director of the Maternal Congenital Heart Disorders Program at Lucile Packard Children’s Hospital Stanford says it’s important women are aware of their risk factors before becoming pregnant.

“It’s recommendable that every woman plans her pregnancy, takes prenatal vitamins and folic acid supplements at least six months before conception, and in an ideal world has a preconception well visit with her primary care or general OB-GYN to go over future pregnancy, Bianco advised. “The main idea is to identify any risk factor to the future pregnancy, such as metabolic syndrome, diabetes, HTN [high blood pressure], obesity, malnutrition, tobacco or drug use, and potential teratogenic medications [drugs that can impact the development of a fetus]. Treatment can be started and or modified before conception.”

However, even if a woman has no risk factors, experts say she should still take steps to ensure her heart remains healthy during pregnancy and following birth.

“All women should take steps to monitor their heart. Prevention is critical for all women. Statistics show that more than [70] percent of [adults] aged 20 and older are overweight or obese. With 1 in 3 women living with some form of cardiovascular disease and women accounting for almost half of all cardiovascular deaths, it’s critical that women be in charge of their heart health early on,” Steinbaum said.