What You Need to Know About Heart Rate During Pregnancy

Pregnancy is an exciting time, no doubt about it. But let’s be honest: It also comes with about a billion questions. Is it safe to work out? Are there restrictions? Why the heck is everyone telling me I need a heart rate monitor?

If you’re not careful, the questions can quickly become overwhelming, and it’s tempting to sit on the couch for the entire pregnancy. When I first became pregnant with twins, it was labeled “high-risk,” as all multiple pregnancies are. Because of that, I was slapped with all sorts of restrictions on activities. Being a very active person in my day-to-day life, this was really hard for me to wrap my brain around, so I went in search of multiple opinions. One piece of advice I got time and time again: Get a heart rate monitor, and keep you heart rate below “X” while exercising.

But the truth is that the guidelines about exercising while pregnant have been adapted from overall physical activity and public health literature, reports the National Institute of Health (NIH). In 2008, the U.S. Department of Health and Human Services (HHS) issued comprehensive guidelines on physical activity, and included a section stating that healthy, pregnant women should begin or continue moderate-intensity aerobic activity during pregnancy, accumulating at least 150 minutes per week. But there’s little information about heart rate, specifically. And in 1994, the American Congress of Obstetricians and Gynecoligists (ACOG) removed the recommendation that many obstetricians still follow—keeping heart rate to less than 140 beats per minute—because it was found that tracking heart rate during exercise is not as effective as other monitoring methods.

What gives? We’re constantly told to measure our heart rate during exercise as a way of really deciphering how hard we’re working. So why wouldn’t we do the same during a pregnancy, when there’s another life to monitor?

“Using heart rate as a measure of exertion might be unreliable in pregnancy because of the many physiological changes that happen in order to support a growing fetus,” says Carolyn Piszczek, M.D., an OBGYN in Portland, OR. Example: Blood volume, heart rate, and cardiac output (the amount of blood your heart pumps per minute) all increase in a mother-to-be. At the same time, systemic vascular resistance—AKA the amount of resistance that the body has to overcome in order to push blood through the circulatory system—decreases, says Sara Seidelmann, M.D., Ph.D., researcher in the cardiovascular division at Brigham and Women’s Hospital in Boston. All of those systems work together to create a balance that allows enough blood flow to support both mom and baby during exercise. “Because of all of these changes, your heart rate may not increase in response to exercise in the same way that it did before pregnancy,” says Seidelmann.

So if monitoring heart rate is out, what should you do instead? Pay attention to perceived moderate exertion—otherwise known as the talk test. “During pregnancy, if a woman is able to comfortably carry on a conversation while exercising, it is unlikely that she is overexerting herself,” says Seidelmann.

Now, what does this all mean for working out while pregnant? According to the Centers for Disease Control Prevention (CDC), pregnant women should aim to get at least 150 minutes of moderate intensity aerobic activity every week. Moderate intensity is defined as moving enough to raise your heart rate and start sweating, while still being able to talk normally—but definitely not sing. (Usually, a brisk walk is close the correct level of exertion.)

And don’t forget, working out while pregnant is beneficial to both you and baby. Not only can it reduce back pain, promote healthy weight gain during pregnancy, and strengthen your heart and blood vessels, but it may also decrease your risk of gestational diabetes, preeclampsia, and cesarean delivery, according to ACOG. (PS: Did you know this birthing method even existed?) Still, that doesn’t mean you should go balls-to-the-wall and adopt a routine you’ve never tried before. In fact, that’s the exact opposite of what you should do, and these are some ways to tell whether you’re pushing too much. But if you’re healthy and your doctor gives you the go-ahead, it’s usually safe to continue regular physical activity. Just use that talk test to help keep you in line, and maybe leave the heart rate monitor at home.