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What the research says about exercise, fertility, and early pregnancy

What the research says about exercise, fertility, and early pregnancy

7 min read

When it comes to exercise, there’s a lot of info out there to sort through. It can be especially confusing to understand what advice to follow if you’re trying to conceive, either naturally or with assisted reproductive technologies.

As a reproductive endocrinologist, I spend a lot of time chatting with patients about lifestyle factors and exercise. Patients ask me all the time: “How much should I be exercising? Does too much or too little exercise affect my ability to get pregnant?”  

Below, we’ll go over some common questions regarding exercise and its impact on reproductive health, fertility, and pregnancy. One important caveat to remember is that everyone’s body has unique needs. The recommendations you receive regarding exercise might be pretty different from the recommendations your friend will receive — advice may vary greatly depending on your overall health, any chronic conditions you may have, and current exercise regimen. That’s why it’s so important to talk about all of this with your doctor, especially if you have any pre-existing health conditions.

Before we dive in: general recs on exercise

According to the Centers for Disease Control (CDC), physical activity may have an immediate and positive impact on brain health, bone and muscle strength, and weight management. Additionally, it may also reduce your risk of cardiovascular disease, type 2 diabetes, and metabolic syndrome. The World Health Organization (WHO) recommends adults between the ages of 18 and 64 engage in 150 minutes of moderate intensity physical activity which may include walking, cycling, or doing sports.

Does too much (or too little) exercise impact fertility?

Overall, exercise is good for you. When we think of exercise and reproductive health, our question becomes does too much or too little exercise help or hurt fertility — and can exercise improve some endocrine conditions such as irregular periods or polycystic ovary syndrome (PCOS)?

In short, exercise is recommended for most people with ovaries before they’re trying to conceive, and the benefits outweigh the risks. One prospective study of over 17,000 women without a history of infertility were followed over several years to assess time to pregnancy. The researchers demonstrated that women who followed five or more low-risk lifestyle factors (such as a eating balanced meals and getting in at least 30 minutes of physical activity per day) had a 69% lower risk of ovulatory disorder infertility. This study suggests that ovulatory infertility may be preventable through nutrition and exercise choices.

Additionally, women with PCOS and irregular cycles who lose 5-10% of their body weight may see a positive impact on ovulation (since 40-80% of people with PCOS have higher body-fat percentages, which may also contribute to irregular or absent ovulation).

How does exercise impact male fertility?

Overall, the data is sparse regarding exercise and male fertility. However, one study assessed sperm parameters in relation to physical activity and found no difference in sperm quality based on physical activity, with the exception of men who biked more than five hours per week. This group of men was found to have lower sperm concentration and total motile sperm.

While this effect on sperm has been shown in other studies, too, the exact mechanism is unknown — but possible theories may be related to increased core scrotal temperature or mechanical trauma (such as compression).

Steroids have been shown to negatively impact sperm concentration, motility, and morphology as they inadvertently lower the concentration of testosterone in the male testis (due to a decline in male reproductive hormones that are secreted by the brain), which is vitally important for normal sperm development and maturity. This is why it’s so important that men who take steroids, or other anabolic hormones that facilitate muscle growth during weight training or bodybuilding, talk to their doctor about the medications they’re taking.

So, if you’re trying to conceive… how much should you be exercising? (And is there a risk to too much exercise?)

Studies have been mixed on the exact “right” amount of exercise that may negatively impact the chance of pregnancy.

One study published in 2012 and another published in 2016 both concluded similar findings, that moderate exercise is beneficial to almost all people with ovaries who are trying to conceive. They also concluded that vigorous exercise (defined as >5 hours of high intensity exercise per week — skip ahead for what this means!) may only be beneficial in women with high body-fat percentage and may actually reduce chances of getting pregnant for other women.

What’s considered moderate-intensity exercise? This will be highly individualized. Someone who regularly trains for marathons will have a different perception of exercise intensity compared to someone who just started an exercise routine last month.

The most important aspect is to make sure you enjoy the exercise you’re doing so that you’re more likely to continue it.

According to the Borg Rating of perceived exertion, a score of 13-14 (or somewhat hard) is considered moderate intensity. (“Brisk walking or other activities that require moderate effort and speed your heart rate and breathing but don’t make you out of breath.”) Another way to measure exercise intensity is the “talk test.” If you can talk throughout your workout, you are likely doing a moderate intensity workout. We will stress again that everyone is different when it comes to perceived difficulty of a workout; therefore, it is important to develop an individualized plan with your doctor.

As far as “best” exercises to partake in when trying to conceive? In short, there are no good studies to document superiority of one exercise over another. Walking, running, yoga, pilates, cycling, swimming, and strength-training are all good options when you’re thinking of becoming pregnant if those exercises are considered moderate intensity for you. The most important aspect is to make sure you enjoy the exercise you’re doing so that you’re more likely to continue it.

What’s the deal with over-exercise and conception?

In this review of different studies, one study showed that ovulatory women who engaged in vigorous physical activity over 60 minutes/day may be at a higher risk of ovulatory dysfunction, but exercise between 30-60 minutes/day had a reduced incidence of anovulation.

The ovulatory dysfunction in women who exercised over 60 minutes/day may be due to a higher overall energy drain and dysregulation of leptin and cortisol, two hormones that regulate appetite and stress response, respectively. When these hormones are being secreted by the body in higher or lower amounts, they can negatively impact ovulation.  

Another study suggested that women who exercised (with the group average being 457 min/week) had higher rates of anovulatory cycles and shorter luteal phases.

What about exercise during the two-week wait?

The “two-week wait” refers to the luteal phase of your menstrual cycle that begins after ovulation (and possible fertilization of an egg) and lasts until either pregnancy occurs or the breakdown of the corpus luteum begins (and you get your period). In general, it’s hard to state whether exercise may affect implantation for a few reasons. First, because we don’t have a good test to determine exactly if/when implantation occurs, it is difficult to study whether exercise may impact implantation. Second, there are so many other biological mechanisms that need to happen correctly for successful implantation to occur, so it would be difficult to pinpoint the exact role exercise may play.

The takeaway? Exercise, in moderation, is likely beneficial for almost all people with ovaries. Vigorous exercise in some women may do more harm than good by leading to an energy deficiency which could negatively impact ovulation and, subsequently, fertility.

Do the exercise recommendations change if you’re doing assisted reproductive technologies (like IUI and IVF)?

There is significantly less research on the “right” exercises to do if you are undergoing fertility treatments.

Many patients going through fertility treatment, and especially IVF, are told “minimal to no exercise during IVF.” The reasons for this are not necessarily due to a negative impact of exercise on IVF outcomes. One study of women undergoing IVF noted that doing moderate to vigorous activity had no impact on implantation, clinical pregnancy, or live birth rates.

The main issue with exercise during IVF has to do with the risk factor associated with IVF of ovarian torsion (when the ovary twists around its stalk). During IVF, women take hormonal injections to grow multiple follicles in preparation for an egg retrieval. During that time of hormonal stimulation, the ovaries tend to enlarge significantly, in some women becoming the size of grapefruits! The ovaries are connected to the pelvis by ligaments which also contain their blood supply. When the ovaries enlarge they have an increased risk of twisting on themselves, potentially cutting off their blood supply which can become a surgical emergency (ovarian torsion).

While the risk of ovarian torsion from IVF is small (less than 1%), many physicians will counsel their patients to avoid strenuous or “jarring” activity that may increase the risk of torsion. Some activities that most physicians will describe as a “no-no” during IVF include running, yoga inversions, high-impact exercise, or any other activity that causes the ovaries to shift around in the pelvis.

Let’s talk about exercise once you’re pregnant — what’s the right amount?

Numerous studies recommend that exercise in pregnancy is not only safe, it is recommended. Per the American College of Obstetricians and Gynecologists (ACOG), exercise in pregnancy has been shown to increase the chance of a vaginal delivery as well as decrease the risk of many adverse pregnancy outcomes including:

  • Gestational diabetes
  • Gestational hypertension
  • Preterm birth
  • Cesarean delivery
  • Low birth weight infants

While some modification may be necessary during pregnancy, in general, anyone who is pregnant can continue the exercise routines they were doing pre-pregnancy.

Notable exceptions to this include avoiding contact sports (think martial arts, lacrosse, boxing) and sports where you’re at risk of falling (like skiing or ice skating), scuba diving, and prolonged exposure to high heat. Per ACOG and in coordination with the WHO, if you’re pregnant, you should aim for 150 minutes of exercise per week. Additionally, pregnant people should aim for an exercise intensity that doesn't make your heart rate exceed 140 beats per minute.

One thing to note: it’s generally not recommended to lift heavy loads. One study showed that lifting more than 20kg (or around 44lbs) 10 times a day was associated with a risk of preterm birth.

The bottom line

To sum it all up: Remember, what may be moderate intensity for you may be different from your friend so it’s difficult to say what exercise is “best” — everyone’s body has different needs.

What is most important is finding an exercise program you enjoy and can maintain.

If you’ve taken the Modern Fertility Hormone Test, you can find a deeper dive on exercise and fertility in the Movement report. If you’re new to exercise, but are trying to incorporate it into your life, we definitely recommend speaking to your doctor about ways to start that are safe for you.

Did you like this article?

Dr. Temeka Zore

Dr. Temeka Zore, MD, FACOG is a fellowship-trained reproductive endocrinologist and infertility specialist and board-certified OB-GYN at Spring Fertility in San Francisco.

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