Will running affect my fertility?

Is exercise beneficial for reproductive health?

Regular exercise during pregnancy has been shown to decrease risk of conditions like preeclampsia, gestational diabetes, and also decrease risk of birth complications and benefit baby's health into the future. However, too much exercise can have a negative impact on fertility, especially if very high intensity, high volume and associated with a calorie deficit.

There have been 2 large prospective studies that demonstrated women who did more than 3 to 4 hours of very high intensity exercise per week were about 27% less likely to conceive a pregnancy than more sedentary women. However, the same study demonstrated women who did moderate activity intensity exercise were more likely to conceive a pregnancy by about 15% than sedentary women.

High Intensity Exercise and Fertility 

Underlying reasons for why high volume of high intensity exercise can impact fertility is related to both the likelihood of ovulation occurring, the lining of the uterus (endometrium), and levels of progesterone, which is the female hormone important for implantation of an embryo. Doing high volume of high intensity exercise is associated with increased risk of functional hypothalamic amenorrhoea, especially if associated with a calorie deficit. This can be a complete absence of ovulation or women can still have a regular period but not ovulate in that cycle.

Exercise at high volumes, including in runners, has also been associated with a thinner lining of the uterus, i.e. the endometrium, and a shorter luteal phase of the menstrual cycle, which can impact progesterone production. The most important factor runners and athletes need to control to prevent exercise having a negative impact on their fertility is to ensure they do not have a calorie deficit, i.e. being in an energy deficiency state.

The research 

There was a randomised controlled trial in 2015 which put athletes into short term energy deficiency of 15, 30 or 60%. The control group had an appropriate energy balance. All athletes in the energy deficiency groups had higher risk of menstrual cycles issues such anovulation (not releasing an egg), a shorter luteal phase, and lower progesterone. This study demonstrates the importance of appropriate energy balance for female athletes, but especially if they are trying to conceive.

The recommendation  

Athletes trying to conceive should not cease all high intensity sessions but should limit them to once or twice per week and other exercise sessions being moderate or lower intensity. For women who are having fertility problems, it is critical to have this assessed by a medical practitioner and any associated reproduction conditions diagnosed appropriately.

Women with polycystic ovarian syndrome may benefit from increasing physical activity, which could aid their fertility, whereas women with functional hypothalamic amenorrhoea will likely have their fertility negatively impacted by increasing exercise. For women under the age of 35, if they've failed to conceive after 12 months of trying, review is indicated. Fertility is generally more likely when women are under the age of 35.

However, the reason for recommending review at 6 months for women 35 to 40 is because egg quality declines faster as we age and therefore there is a shorter duration of time to intervene to improve fertility and pregnancy to occur.

Although seeking help with fertility may seem scary, intervention for fertility can often be lifestyle related and does not always mean progressing to IVF or other invasive treatments.

Fertility testing 

Women often wonder if they can check or know if they’re fertile.

There is no accurate way to test someone's fertility apart from trying to conceive a pregnancy, obviously this a very involved test and not appropriate unless someone is trying to conceive.  The AMH level tests egg reserve and does not predict fertility and a high or low AMH can give false reassurance or anxiety.

Online companies claiming to test your fertility are misleading and not evidence based.

I reassure my patients that women who have a regular menstrual cycle, are below 40 and especially below 38, with no specific medical conditions that impact fertility, they should consider themselves fertile until proven otherwise.

If you’re a woman runner, please do not think you need to stop running if you want to try and conceive a pregnancy.

Exercise is incredibly beneficial for our health, including our reproductive health. Exercise also decreases risk of postnatal depression and should not be avoided before or during pregnancy, but some adaptations may be required. Please talk to your doctor or obstetrician for further advice on exercise and running for fertility and pregnancy.