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In the fall of 2019, Kiera C. was training for the New York City Marathon and finally felt like she was ready to start trying to conceive. “Part of me was always afraid of the pregnancy journey,” says Kiera, now a mom to a 15-month-old, “but it was on a 15-mile run that I realized I actually had all of the tools I needed to get through it.”
Marathons, she says, are the ultimate metaphor. Kiera liked standing at a start line, staring down a challenge, knowing she had the grit to tackle what was ahead. “That’s what pregnancy was in my mind: a long, unknown journey with good parts and uncomfortable parts, a lot like marathons. Running made me feel ready for this next step in my life,” she says.
The Wednesday before the marathon, she found out she was pregnant. She felt conflicted about going forward with the race. For runners, fertility and the sport they love have a complicated, nuanced, often confusing connection.
On one hand, exercise (including running) is a healthy and encouraged part of trying to conceive and pregnancy. The Department of Health and Human Services recommends “at least 150 minutes of moderate-intensity aerobic physical activity per week” for pregnant people and that those “who already do vigorous-intensity aerobic physical activity, such as running, can continue doing so during and after their pregnancy.”
On the other hand, other guidelines warn about the risks of “too much exercise.”
“Some research shows exercise is important for overall health and wellbeing—including fertility—but other research warns against exercise negatively impacting fertility,” says Dr. Lora Shahine, reproductive endocrinologist at Pacific NW Fertility in Seattle and host of the Baby or Bust podcast.
“I found all of the studies I could on the topic and emailed a doctor who gave me his blessing to run the race if I felt up to it,” Kiera says.
So she did. And the race went well. She PR’d. She felt great. Then, the Tuesday after the marathon, she started bleeding at work. “I went to the ER, and was told it was a miscarriage.”
Pregnancy loss, particularly early pregnancy loss like Kiera’s, is common. About 10 to 20 percent of known pregnancies end in loss (the actual figure is likely higher; many pregnancy losses occur before pregnancies are known).
Some runners notice that loss plants a seed in your mind: Could running impact fertility?
“I definitely felt low in the weeks that followed,” Kiera says, “but I made a very true effort not to blame myself or my training.”
Talk to a reproductive endocrinologist, like Dr. Shahine, and they will tell you that the research on running and how it impacts or doesn’t impact loss and infertility (defined as not being able to conceive after one year of unprotected sex or 6 months or longer for people over 35) is, at best, mixed.
Some studies in athletes with high levels of intense exercise show that this type of exercise could have a negative impact on menstrual cycles, ovulation, and fertility. There’s also research to suggest that in people with a history of loss, vigorous exercise is linked with very early pregnancy loss.
Other studies find lower fertility rates in women of normal weights with a sedentary lifestyle. A review of 100-plus studies on exercise and pregnancy found that even vigorous fitness wasn’t tied to pregnancy loss risk; another review of 23 studies published in the BMJ found the same: Prenatal workouts weren’t linked with increased odds of miscarriage.
Moderate exercise can be hard to define—impossible even—especially for the highly active. And when it comes to exercise and fertility, it’s hard for data-driven athletes and well-intended providers alike to know where exactly to draw the line.
The result: “Recommendations from healthcare providers vary and patients looking for answers can be left wondering what to do,” Dr. Shahine says.
Take Deirdre, a mom of three in Westchester, New York. She has been a runner since high school and says that a year-and-a-half into trying, her doctor told her to cut back on exercise with little to no guidance beyond that.
Emma Bromley, a mom to a 6-year-old in Los Angeles, says that when she started her fertility treatments years ago—having been a recreational runner for about 14 years—she was “told not to run or do anything high impact.”
(Dr. Shahine points out that some people get a general “no exercise” guideline throughout in vitro fertilization (IVF) due to the increased risk of ovarian torsion, which is when the ovary twists, cutting off blood supply. It’s rare but when it happens, it’s a medical emergency.)
Bromley followed her doctor’s advice and stopped running. “When you’re putting in all that time, effort, multiple daily injections, not to mention thousands of dollars, it’s hard to want to ignore the doctor’s advice,” she says. At first, giving up running for a short period of time felt like “a small sacrifice,” she says, but once she got pregnant and found out she had a high risk pregnancy and had to continue her hiatus per her doctor’s orders, things felt much harder.
Deidre says that cutting back on exercise was “so hard to do.” She adds: “Running was my life and cutting back depressed me.”
Kiera says that she tried not to water that “was-this-something-I-did” seed and continued running shortly after her loss.
Every person and situation is different. Generally speaking, says Dr. Shahine, “those who love running shouldn’t have to give it up while trying to conceive.” But, she says that modifications to how hard or far you run are often worth considering. She notes that “pushing your body too hard releases cortisol, the stress hormone” and that this can shift your body toward a “fight or flight stress response” and away from a focus on reproduction.
Throughout her pregnancy, Bromley stuck to hiking. “My young pup and I hit up every hiking trail in L.A. we could find.”
Deidre ran throughout her pregnancy, adding “I had no issues having baby number two or three.”
Says Kiera: “I truly believe my loss would have happened regardless of whether I ran the marathon or not. I got pregnant while training for a marathon, so that’s how my body was built at that point in time.”
It’s an important point for runners who find themselves feeling guilt or questioning their lifestyle: Most pregnancy losses happen because a fetus isn’t developing as expected. About half are due to chromosomal abnormalities that occur due to “errors that occur by chance” and “not problems inherited from the parents.”
After her loss, Kiera says that “running still felt like an important part of my trying to conceive journey. It was the very thing that empowered me to move forward. And when I got pregnant again, months later, my running background made me feel more confident going into labor.”
“There is no one guideline that fits every person trying to conceive. There is no one heart rate to shoot for, number of miles to run, and universal recommendations. Consider staying moving but modifying strenuous workouts,” says Shahine.
Everyone’s modifications (if any) throughout trying to conceive or pregnancy will be different and will likely change throughout a journey. This timeframe is often a good first test in listening to your body—and working with your healthcare team to find out what is best for you.