What Do We Actually Know About Exercise And Pregnancy?

During all three of my pregnancies, as my body grew and shifted in ways that made it feel foreign, I found comfort in movement. Walking helped me feel grounded. Pilates helped me feel connected to my changing form. Weight training helped me feel strong. But the physical benefits weren’t nearly as meaningful as the emotional ones. Between preeclampsia, a late-term loss, and placenta previa, my three pregnancies all felt like gauntlets, but focusing on what was in my control — putting one foot in front of the other on a walk, lifting a dumbbell — helped me to weather the anxiety.

Historically speaking, I know I'm lucky: Less than 40 years ago, women were unequivocally told to take it as easy as possible while pregnant. It was only in 1985 that the American College of Obstetricians and Gynecologists (ACOG) published its first guidelines for exercise during pregnancy. Today, the group encourages most low-risk pregnant people “to engage in aerobic and strength-conditioning exercises before, during, and after pregnancy.”

Since then, research has revealed a host of benefits for exercising during pregnancy for both pregnant people and babies. “We now know a whole lot more about the safety and efficacy of being active,” says Rachel Tinius, Ph.D., an assistant professor of exercise science at Western Kentucky University, who researches the effects of physical activity during pregnancy — and ran the Boston Marathon while 12 weeks pregnant with her fourth child. “The research that we have shows overwhelmingly how much better moms do with delivery, with fetal outcomes, postpartum outcomes, mental health, blood pressure, [and] gestational diabetes” when they’re active, she says, all of which positively impacts the developing fetus, too.

For years, pregnant women were told by doctors not to let their heart rate go above 140 beats per minute, despite the fact that this advice wasn’t based on any evidence.

And yet, outdated fears persist around pregnant women and exertion, which may help to explain why, according to some estimates, only 40% of pregnant women exercise during pregnancy. Women who do work out while pregnant still receive unsolicited commentary from family or even strangers, questioning their safety and the safety of their unborn child. When I polled people on social media about their experiences with exercise during pregnancy, I heard stories of women who were warned by fellow gymgoers that doing squats with weights would make the baby “fall out” (nope), or that too much cardio would make their future child hyperactive (a hard no). Powerlifters were told by their doctors to switch to tiny 10-pound weights.

Kyle Georgina Marsh, a Pilates teacher and strength coach based in New York City, balked when her obstetrician advised her to scale back her physical activity simply because she was pregnant. When Marsh pushed back, her doctor told her, “You can keep doing these things, but if you end up injured or compromising your pregnancy, don’t say I didn’t warn you.” (Marsh switched doctors.)

While the last four decades have seen a major uptick in research exploring exercise during pregnancy, the scientific community is still playing catch-up for the complete void of data that existed until — well, very recently. Beyond simply filling the void, researchers are also working to replace earlier, misguided beliefs, recommendations, and fears with evidence-based information. For example, when ACOG released its first physical activity guidelines for pregnant women in 1985, the group cautioned that pregnant women should be sure their heart rate did not go above 140 beats per minute. For years, this advice was standard in doctors’ offices — despite the fact that, according to several researchers, it wasn’t based on any evidence.

In the absence of studies examining the effects of exercise on pregnancies, obstetricians simply came up with a number that seemed reasonable, says Tinius. “It was based on a bunch of smart doctors that sat down together and basically said, ‘Well, let's protect ourselves and make sure that our patients are safe,’” she told me.

Evidence now suggests that, for many pregnant women, it is safe — and can be beneficial — to work out at a moderate-to-high intensity, particularly if they were active before pregnancy. And yet, several pregnant women I spoke with report being told — in 2024 — to keep their heart rate below 140, for no good reason. The same goes for lifting heavy objects. “We know so much more now,” says Tinius, but “it was just 30-something years ago the recommendations were completely different.”

The fact that the common wisdom about pregnancy exercise has changed so dramatically in roughly one generation means that a lot of the previous advice is still circulating, and many people are skeptical about defying it. “[Pregnancy] is a time that is just filled with stress and anxiety and worry,” says Tinius, and so “sometimes the emotional can outweigh logic.” The challenge is translating scientific advances “into actually getting people moving, and not being afraid to move.”

Evidence now suggests that, for many pregnant women, it is safe — and can be beneficial — to work out at a moderate-to-high intensity.

“We have an information dissemination crisis,” sayss Gráinne Donnelly, a pelvic floor physical therapist and editor of the Journal of Pelvic Obstetric and Gynaecological Physiotherapy. In her research, she has found that many women receive no advice about physical activity during pregnancy and postpartum. “I think education and public health messaging has a huge importance, and we need to improve on it.”

On top of this, earlier guidance has also presented a challenge for researchers who want to study exercise during pregnancy. “I think the biggest limitation [to more research] is these limitations we have put onto the research area previously,” like keeping pregnant women’s heart rates below 140 beats per minute, says Margie Davenport, Ph.D., a professor of kinesiology at the University of Alberta who runs a lab dedicated to researching physical activity during and after pregnancy. “As soon as you have these limitations that really get into the social fabric of our lives, it's really difficult to propose these studies, get them funded, and get them approved by the ethics board, because they're seen as being really risky,” she says. “But in my opinion, the riskier thing is not doing the research.”

So what do we know? For starters, ACOG recommends that pregnant women get at least 150 minutes of moderate-intensity aerobic activity every week, the same recommended dose of weekly exercises for non-pregnant people. While the latest guidelines don’t suggest a specific amount of strength training weekly, the group says strength conditioning is generally beneficial.

Researchers also agree that, for most women who are experiencing normal-risk pregnancies, staying active during pregnancy can be an “exceptionally powerful” tool for boosting health and well-being, says Davenport. Physical activity has the potential to ease back pain and constipation, strengthen your heart and blood vessels, and decrease your risk of gestational diabetes, preeclampsia, preterm delivery, and cesarean birth. Some women also find that moving helps with nausea. Exercise during pregnancy can lead to a speedier recovery postpartum, too.

And crucially, for many women — particularly those who exercised regularly before pregnancy — staying active can support their mental health, says Davenport. In 2021, she and her team reviewed population studies looking at the impact of exercise on anxiety and depression during pregnancy and found that women who stayed very active reduced their risk of both depression and anxiety by around 32%, compared to control groups. “We are just starting to scratch the surface” of understanding the potential of exercise for mental health during pregnancy, Davenport says — in part because the scientific community has only been studying pregnant people’s mental health for a little over a decade.

Exercise during pregnancy also benefits the fetus, says Dr. Cynthia Gyamfi-Bannerman, M.D., a professor of maternal-fetal medicine at the University of California-San Diego, who co-authored ACOG’s most recent guidelines on exercise during pregnancy. This mutually beneficial relationship is especially clear when it comes to preterm delivery. “We know that stress is a pretty big cause of preterm birth,” she says, and “exercise in and of itself releases endorphins that mitigate stress.”

But even when physical activity doesn’t prevent complications or less-than-ideal outcomes, it can still benefit a pregnant person by simply helping them feel better, calmer, and stronger. This was the case for me. Despite staying active throughout my pregnancies, I developed multiple complications — and yet, I’m convinced that my movement habit helped me endure these ordeals far better than I could have if I’d been forced to sit still.

The gaps in knowledge that scientists are working to fill are particularly wide at the far ends of the exercise spectrum, says Davenport. That includes pregnant people who have medical conditions for which doctors advise against exercising, and elite athletes who want to continue to train at the highest level during pregnancy. “People who have contraindications to exercise — we actually know very little about it,” says Davenport. “Many of those contraindications are based on theoretical issues rather than actual evidence. But that [research] is certainly building.”

More than two dozen athletes have competed in the Olympics while pregnant, several of whom have medaled.

At the other end of the spectrum are athletes who regularly exceed current recommendations with high intensity, long duration, and high volumes of activity. That we know even less about, says Davenport. This dearth of knowledge can be especially challenging for elite athletes who want to continue to train or compete during pregnancy. “It creates a lot of anxiety, and oftentimes distress, because [we] don't have evidence to demonstrate what the true limits are, or if it's safe or not,” she says.

Dr. Megan Roche, M.D., Ph.D., an Olympic trail runner who researches and coaches pregnant athletes, agrees. “That's still a big question in my mind,” she says. “If an athlete goes out and runs an all-out 5K, there's just not enough evidence to be like, how does this support a developing fetus?”

While they wait for the research to catch up, many pregnant athletes forge ahead with competition, trusting their bodies. Serena Williams famously won the 2017 Australian Open while pregnant, and elite runners now win races while pregnant. More than two dozen athletes have competed in the Olympics while pregnant, several of whom have medaled.

Both Davenport and Roche stressed the need for more high-quality studies — which, again, can be difficult to get approved, since they might require pregnant women to push their bodies to a limit that isn’t currently sanctioned by medical guidelines.

And yet, just because some pregnant people can push themselves physically while pregnant doesn’t mean everyone should. Since Jane Fonda released her groundbreaking pregnancy workout in the 1980s, fitness culture has come for pregnancy full-throttle. To be pregnant in 2024 is to be barraged with images and videos of women working out until the day they give birth, their abs somehow still visible over their bumps. As pregnant athletes have become more commonplace — crossing marathon finish lines, CrossFitting, teaching workout classes — some women now feel pressure to keep working out as if they weren’t pregnant at all. Exercise can feel like one more item on a never-ending list of pregnancy wellness to-dos. And women who need to temper their movement habits during pregnancy for legitimate health reasons now fear the potential repercussions of not moving.

Sometimes in the cultural enthusiasm for encouraging pregnant women to work out, the nuances of what it actually feels like to exercise while pregnant can get overlooked. The reality is that, during pregnancy, women’s bodies transform in both visible and invisible ways that can have a profound impact on their experience of exercise and movement. Understanding these changes can help to both reduce women’s anxiety around exercise and set realistic goals, experts say. Some of these changes involve the cardiovascular system. When pregnant, your resting heart rate tends to increase, and your heart rate may spike doing relatively gentle activities, such as walking up a hill. This is, in part, because your blood volume practically doubles during pregnancy, and your heart has to work harder to pump it through your body and to the developing fetus. “Pregnancy is like a stress test,” says Gyamfi-Bannerman. “And it’s essentially like being on a stress test for your entire nine months.” It’s taxing.

Fatigue and nausea can also weigh down even the most motivated exercisers. “The first trimester is so hard,” says Roche. “I've seen athletes struggle with momentum after the first trimester, even if things start feeling better into the second. Sometimes picking up and restarting exercise can be really hard.”

Then there are the hormonal changes, including a surge of the aptly-named hormone relaxin, which causes your joints and ligaments to become looser and less stable, particularly in the third trimester. These changes are beneficial for uterine growth and delivery, but they can make certain workouts more challenging. “With athletes that I've worked with, I've seen a lot of rolled ankles or sprained ankles, just from the ligament instability,” says Roche. “And then things like pelvic pain or hip pain.” For this and other reasons, back pain is very common, too.

As your pregnancy progresses, you may also feel out of breath if you lie flat on your back, since your growing uterus can press on one of the main arteries that supplies oxygen to your brain. You’ll want to avoid this position for long stretches. As your uterus grows, your center of gravity can change, too.

“Maintaining your balance is not going to be the same as it was before you were pregnant,” says Gyamfi-Bannerman. “So understanding that, and factoring that into what you do, is important.” (Many pregnant women also report feeling more comfortable when wearing a belly band or compression garment, such as support leggings or bike shorts, during physical activity.)

“You really cannot compare yourself to the person next to you or to the person three lanes over, because their story is very different from yours.”

More than anything, Roche says, during pregnancy, you’re best off listening to your body, and asking yourself: How does this feel? Does it feel reasonable? “It can be stressful to have heart rate data pop up during a run. Seeing that data at all times is actually kind of overwhelming. It's like, what is my heart doing now?” she says. The guidance around exercise during pregnancy has “evolved to become … more intuitive with the body.”

If you were extremely active before pregnancy and you can maintain your workout without any negative side effects, you can probably keep doing what you’ve been doing, she says. But if you’re new to working out, “it's really about easing into it and building into it slowly.”

The experts I spoke with also emphasized that a pregnancy exercise routine doesn’t have to look like a sweaty session at the gym. Walking, yoga, and even running errands are all beneficial. “We talk a lot about doing 150 minutes of moderate-intensity physical activity,” says Davenport, “but what is often missed is that even well below those recommendations, there are significant benefits.” Any movement is better than no movement.

Experts also stressed that every body, and every pregnancy, is different. “You really cannot compare yourself to the person next to you or to the person three lanes over, because their story is very different from yours. And their body is very different from yours. And what they're feeling is different from yours,” Tinius says. “Just having an appreciation for what the body is doing, and giving yourself grace in the process” can help you focus on what’s right for you, says Roche. “It's not going to look the same for everyone.”

Danielle Friedman is an award-winning journalist who focuses on the intersection of health, sexuality, and culture. She is the author of Let’s Get Physical: How Women Discovered Exercise and Reshaped the World, and her writing has also appeared in The New York Times, The Cut, Vogue, Glamour, Harper's Bazaar, the Washington Post, NBC News, InStyle, The Daily Beast, Health, and more. She has previously written for Romper about how to reframe your relationship with exercise and whether teens should take Ozempic for weight loss.