Photo by David Jaewon Oh
Editor's note: Experiences during pregnancy vary from person to person; this story is not a substitute for medical or safety advice. Please consult your physician to talk about what is right for you.
When you're pregnant, your body goes through a variety of changes. To name a few: The volume of blood pumping through your veins rises by 30 to 50%, and your resting heart rate increases. It's common to feel nauseous, thanks to changes in estrogen and human chorionic gonadotropin (HCG) hormone levels. The joints and ligaments in your pelvis gradually loosen to prepare for labor.
Despite these and other marked shifts that can make movement feel different, exercising during pregnancy offers measurable benefits. Engaging in activity like running during pregnancy can reduce a person's risk of developing gestational diabetes and high blood pressure. It's also associated with a shorter duration of labor and lower rates of pre- and postnatal depression. For the baby, prenatal exercise may mean a lower risk of being born large for gestational age, and fewer birth complications.
However, societal misconceptions and a lack of research about prenatal exercise mean that many childbearing people are uncertain about whether it's safe to run while pregnant. Health guidelines can be vague or inconsistent, and public opinion may further muddy the waters. That said, the science is clear: You can continue to run while pregnant, so long as you do not have a medical reason to avoid exercise. Listening to your body, tracking physical biomarkers, and talking with your care providers can help you navigate the sometimes confusing landscape of prenatal running.
Continue to read more, or use the links to go directly to each section:
- The History of Running While Pregnant: Where the research began
- How to Run While Pregnant: General guidelines and how to measure intensity
- Vigorous Activity: Are high-intensity runs safe while pregnant?
- When to Stop Running: Signals to prioritize rest and see your doctor
- How to Talk to Your Doctor: Seeking advice and support as you navigate prenatal running
The History of Running While Pregnant
Experts say that more research is needed on the risks and benefits of running while pregnant. This is in part due to the fact that pregnant people can be difficult to study from a practical and ethical perspective. There has also been less medical research conducted on women, generally.
In her 2022 book Let's Get Physical, Danielle Friedman documents the history of women in running. She notes that prior to the late-1960s, "athletic officials believed that if a woman ran more than a mile or two at her full capacity, the effort would harm or even kill her." Ideas about women's running slowly began to change in 1967 when Kathrine Switzer ran all 26.2 miles of the Boston Marathon despite efforts to forcibly remove her from the race.
Studying physical activity during pregnancy is also new. Kelly Evenson, a professor of epidemiology at the University of North Carolina, Chapel Hill, who studies physical activity during pregnancy found that the earliest recommendations for physical activity during pregnancy were influenced by social norms, as opposed to research. In 1949, for example, the U.S. Children's Bureau deemed prenatal physical activity acceptable as long as pregnant people focused on housework, gardening and daily walks up to one mile. Pregnant people were advised to avoid sports altogether.
The rise of women's running and an uptick in research about the benefits of staying active during pregnancy means experts are now honing in on more practical, useful recommendations for pregnant people.
In the future, researchers say we need more studies that look at the postpartum period, too. Gradually returning to aerobic activities after giving birth may shorten recovery times and increase the likelihood of raising active children, but more evidence is needed.
How to Run While Pregnant
Pregnant people interested in running should consult with a doctor to rule out any medical concerns and gather individualized advice about the level of activity that will work for you.
General Guidelines
The American College of Obstetricians and Gynecologists (ACOG) recommends 150 minutes of moderate-intensity aerobic activity weekly, during pregnancy, as long as you do not have a medical reason to avoid exercise. This works out to about 20 to 30 minutes of daily activity, and running can check that box. It's a good idea to strength train, too, to help support the joints and ligaments you use for running.
"Typically, [with running], you're safe to continue doing what you've been doing pre-pregnancy," says Sarah Kaiser, a Seattle-based doctor of physical therapy who specializes in the pelvic floor. She cautions that,"you should stop immediately if you begin to experience red-flag symptoms like vaginal bleeding, abdominal pain, and so on."
For patients who do not currently exercise but wish to become active while pregnant, Kaiser recommends comparatively light-intensity activities like prenatal yoga, walking or bodyweight exercises.
Measuring Running Intensity
The ACOG guidelines are a helpful starting place, but pregnant runners may wonder what constitutes a moderate-intensity run. Is it about heart rate? Perceived exertion? And what about days when you feel great and want to go for an hour instead of 30 minutes?
The answers to these questions get to the heart of why it's so difficult to prescribe prenatal activity in the first place. There isn't a one-size-fits-all approach, and because your resting heart rate increases during pregnancy, judging exercise intensity via typical metrics isn't always reliable for pregnant people. The main thing is to listen to the signals your body sends, experts say. A run that felt moderate one day—meaning your breathing was easy and any discomfort was delayed and minimal—might feel extremely challenging the next.
You may have heard that it's a good idea to target a specific heart rate when running while pregnant, specifically 140 or 150 beats per minute (bpm). This idea emerged from a 1988 study that found that, in some cases, fetal heart rate dropped below 110 bpm (known as fetal bradycardia) when pregnant people exercised with a peak heart rate of 180 bpm. The authors state that this level of exertion followed by fetal bradycardia "may indicate inadequate fetal gas exchange." However, the study doesn't prove that fact, according to xx. Emily Oster, an economist and founder of ParentData, has noted that this research is likely where the guidance to keep one's heart rate under 140 to 150 bpm comes from.
Find your maximum heart rate. The current ACOG recommendation is to keep your heart rate at 60 to 80% of your predicted maximum. To calculate your maximum heart rate, subtract your age from 220.
Researchers, including Evenson, suggest using a combination of heart rate and perceived exertion to figure out the level of running intensity that's right for you.
Use the Borg Scale. Familiarizing yourself with the Borg Scale can help you rate your level of exertion.
- Start out with a "fairly light" effort—think of an easy, warm-up pace.
- In the middle of this effort, pause and collect your heart rate.
- Then, try something a little harder—head uphill or pick up the pace so that you move into the "somewhat hard" range.
- Pause and note your heart rate once again.
This test can tell you how much your heart rate increases between light and moderate activity. Over time, Evenson says, you may not need to measure your heart rate at all; you'll simply be able to feel that you've moved into moderate intensity.
Try the talk test. Another way of thinking about this is called the "talk test." It's as simple as it sounds: You monitor your level of workout intensity based on how easily you can talk through the effort. You should be able to get out full sentences but not sing through moderate-intensity activity, according to the CDC.
What About Vigorous Activity?
Terms like "moderate" and "vigorous" can be confusing because they mean different things to different people. Some researchers consider all running to be vigorous activity, whereas others differentiate between easy and challenging efforts. If you want to incorporate some hard efforts into the mix (like a run where your perceived exertion exceeds the "somewhat hard" range on the Borg Scale), talk to your doctor. Your care provider can take into account your unique medical and athletic history, and help you make the decision that's right for you.
Still, we need more information on high-intensity or vigorous exercise during pregnancy. A 2019 meta-analysis found that brief vigorous aerobic activity—where athletes exercise for no more than 30 minutes at an intensity in which they cannot speak full sentences—is safe during the third trimester for most pregnancies. But, the authors observed that there was less research on exercise during the first and second trimesters, as well as exercise exceeding 90% of maximum heart rate.
We also know little about how these guidelines may apply to elite runners, or athletes with several years of experience who train year-round at a high level. There are isolated examples of elite pregnant people accomplishing incredible feats—think of Alysia Montaño shaving 10 seconds off her previous 800-meter time at the U.S. Track and Field Championships in 2017 or Serena Williams winning her 23rd Grand Slam title at the Australian Open while 20 weeks pregnant in the same year. But, a lack of research on pregnant athletes means we still have a lot to learn about what happens when an elite runner trains and performs while pregnant.
When to Stop Running While Pregnant
The guidelines about when to stop running while pregnant are definite. According to the ACOG, you should stop exercising immediately and seek the attention of a medical provider if you experience any of the following:
- Vaginal bleeding
- Abdominal pain
- Regular painful contractions
- Amniotic fluid leakage
- Shortness of breath before exertion
- Dizziness
- Headache
- Chest pain
- Muscle weakness affecting balance
- Calf pain or swelling
In addition to proper fueling, pregnant runners should aim to stay well hydrated and avoid high heat and humidity to protect against heat stress. As with gauging running intensity, you'll need to listen to your body and note your history to determine how much heat and humidity is "high" for you. A recent study puts a cap at 45 minutes of moderate-intensity activity at 90 degrees Fahrenheit and 45 percent relative humidity for pregnant people, but more research is needed.
Monitor how your body feels before, during and after your runs. Kaiser emphasizes that there's a difference between muscle soreness and pain. "Soreness typically lasts one to two days, and then resolves—that's to be expected." But that's different from sudden, acute pain that's triggered by movement. "In that case, we need to pull back because something has changed."
How to Talk to Your Doctor About Running While Pregnant
It's a good idea to make time to talk to your doctor if you plan to run while pregnant. Experts acknowledge this may be easier said than done because providers' availability can be limited and some clinicians have more education on the risks and benefits of prenatal running than others.
Find a medical practitioner who specializes in exercise. Mallory Marshall is a researcher who has studied people's perceptions of prenatal exercise. "Probably the most important thing is to find a healthcare provider who is knowledgeable and supportive," she says. A practitioner who specializes in exercise or who is active themselves may be more informed. She suggests making it an ongoing conversation. That way, you can compare how you felt during the second trimester with the third, for example.
Advocate for what you need. If your doctor is less educated on running during pregnancy, you might seek out additional support from a physical therapist or a personal trainer who specializes in working with pregnant people. "It's a great idea for pregnant people to go to a [physical therapist] to make sure they're focusing on the right exercises," Kaiser says. "Not only for staying strong, but for preparing for labor."
Consider seeing a pelvic floor physical therapist. You don't automatically need one during pregnancy. However, if you're experiencing leaking or urgency with urination, for example, a pelvic floor PT will have the specialized knowledge to help you address those symptoms.
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