To monitor or not to monitor? That's the question for moms-to-be.

By Heidi Kristoffer
March 17, 2020
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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 pregnancy 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 your pregnancy heart rate below "X" while exercising. (ICYMI, discover what your resting heart rate can tell you about your health.)

Why We Used to Monitor Pregnancy Heart Rate

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 Gynecologists (ACOG) removed the recommendation that many obstetricians still follow—keeping pregnancy 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. (Related: How to Use Heart Rate Zones to Train for Max Exercise Benefits)

What gives? Experts are constantly saying to measure your heart rate during exercise as a way of really deciphering how hard you're working. So why wouldn't you 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 ob-gyn in Portland, Oregon. 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 Seidelmanm, M.D., Ph.D., researcher in the cardiovascular division at Brigham and Women's Hospital in Boston, Massachusetts. All of those systems work together to create a balance that allows enough blood flow to support both mom and baby during exercise.

The thing is, "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.

The Current Recommendations About Pregnancy Heart Rate

Instead of monitoring pregnancy heart rate, the current medical opinion is that it’s best to 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 to the correct level of exertion.)

The Bottom Line

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: Get inspired by these crazy-strong pregnant CrossFit Games competitors.)

Still, that doesn't mean you should go balls-to-the-wall and adopt a routine you've never tried before. 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 pregnancy heart-rate monitor at home.

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