Exercise and Infertility: does it help or does it harm?
There is no doubt that exercise is not only beneficial but also incredibly important for long-term health for the prevention of chronic disease, cardiovascular health and reproductive health. For some reason, when a woman is trying to conceive she is often told (even sometimes by her physician) to hold off on exercising, particularly weight lifting. What we do know is that extremes of anything are never good: complete inactivity resulting in excess weight gain or long hours of strenuous exercise can impact the normal communication between the brain (hypothalamus & pituitary) and ovaries and affect ovulation and pregnancy rates. Interestingly, in a study looking at lifestyle habits of women with infertility trying to conceive, 92% of women were reported to exercise regularly noting a trend towards improving this lifestyle parameter (Domar et al., 2012). In another study looking at short term diet and exercise in obese women, the authors demonstrated that even 12 weeks of consistent diet and exercise prior to conception significantly improved metabolic and hormonal parameters which resulted in improved ovulatory function (Miller,P.B., 2005).
Moderate exercise will not harm your success with fertility treatments and will not diminished your chance of conceiving naturally but it can help; particularly for women who suffer from polycystic ovary syndrome (PCOS) or weight gain. In fact, a meta-analysis (which is a type of study that rigorously analyzes all available published studies to help us better answer a question) showed that both pregnancy rates and live birth rates were higher in women with PCOS exercising regularly compared to women who were not (Mena et al, 2019). Some of the mechanisms for this includes improved metabolic and hormone parameters. With more lean muscle mass comes greater insulin sensitivity (this is good since the less insulin needed, the less sugar is stored, the less it will stimulate the ovaries to promote androgen/testosterone production which can negatively impact egg quality and ovulation) (see more on PCOS and weight lifting).
Ultimately, moderate exercise with a focus on strength training to promote lean muscle mass development can be extremely beneficial for women trying to conceive, during pregnancy and outside of conception altogether.
How much is too much when trying to conceive?
This can sometimes be a tough question to answer. The threshold of exercise before you start to see negative hormonal changes is like most things: it varies per person. But what does the research show?
The U.S. Department of Health and Human Service (USDHHS) recommends a minimum of 30 minutes of moderate to vigorous exercise per day, for a total of 150 minutes per week. This includes women trying to conceive and women who are pregnant as long as there are not contraindications to it (USDHHS, 2008); by the way, this is a small list such as history of heart or lung disease, preeclampsia, preterm labor or rupture of membranes, cerclage, cervical insufficiency to list a few. At least two of these training sessions should include resistance training. For the women trying to conceive, exercise can improve ovulation! A number of studies have demonstrated that women who perform vigorous exercises between 30-60 minutes daily have improved ovulatory function (Hakimi et al, 2017). There is (albeit limited) evidence that suggests vigorous physical activity more than 1 hour per day is associated with ovulatory problems, particularly in underweight women. We know that too much strenuous exercise can certainly impede on your chance of successfully getting pregnant so limiting your exercise to ~60 minutes per day is a good guideline to follow.
When it comes to early pregnancy, many women are fearful to continue on their exercise journey for fear of negatively impacting their pregnancy, or worse, causing a miscarriage. One meta-analysis (where they collectively analyze data from multiple research studies) as well as findings described in a review paper, confirmed that the overall data from 135 studies concluded that moderate to vigorous exercise did NOT increase the risk of miscarriage, preterm birth, regardless of the intensity or frequency of the workouts but it actually helped reduce maternal and fetal complications during pregnancy (Davenport et al. 2018 & Weissgerber et al. 2006). According to the American College of OBGYN, women who perform high intensity workouts in the form of cardio and strength training, should continue to do so during pregnancy and the postpartum period as this results in reduced risk of gestational diabetes, C-section, operative vaginal delivery (ACOG Committee opinion #804). Mind you, once again, of the studies available, the workouts were limited to 60 minutes so we don't have much data for longer workouts.
Ultimately, exercise is of great benefit with only a small risk of injury as long as proper form is maintained and should be performed unless you have one of the few contraindications (click here for the full list). For more on exercise in pregnancy refer to the ACOG committee opinion.