Is it okay to exercise on my most fertile days?

Varvara May 05 2022

There was once a popular notion that sport is unhealthy for women since it endangers fertility. What is it about this claim? Should women who want to become pregnant refrain from exercising? No. But there is a “but”.

Sport does not affect fertility. Even if you want to get pregnant, there is absolutely nothing against the sport. Exercise is healthy and reduces stress. But there is one exception: too intense sport and lack of energy is bad for fertility. The combination of both can make pregnancy more difficult or even prevent it.

When weight loss is not good for fertility

Exercising too much while reducing calorie intake can be devastating because a lack of energy has a sensitive effect on fertility. Biology has taken precautions: In times of famine, the body waits to have children until sufficient food is available again.

Due to the lack of energy, the body thinks it is in an “emergency situation” and menstruation becomes irregular. Studies estimate that around 60 percent of women who play professional sports are affected. Too much exercise can greatly shorten the luteal phase which reduces the chance of becoming pregnant. 

Another disorder is the absence of ovulation despite regular periods. The reason for this is a too low estrogen level. Estrogen is no longer sufficient to trigger the chain reaction necessary for ovulation. The most serious is the complete absence of the period.

The risk of hypothalamic amenorrhea

Hypothalamic amenorrhea, or simply put, the absence of periods, affects very active, fit, and slim women. Intensive sport and low food intake put the body under constant stress. Many women only notice that they are no longer menstruating when they stop taking the contraceptive pill. But without a cycle, it is impossible to get pregnant. 

In addition, symptoms of hypothalamic amenorrhea include digestive problems, bone loss, fatigue, decreased sex drive, dry hair and skin, and an increased risk of heart disease. 

So is it safe to exercise when trying to get pregnant? 

The problem is not the sport, but the lack of energy supply. All symptoms, from hypothalamic amenorrhea to irregular menstrual cycles, can be reversed in most cases. Fertility can also be restored. 

The recipe is simple: You should exercise less for the moment and eat more. It's often just a few extra pounds that make the difference. Once your period has returned and normalized, you can go back to your usual exercise routine, provided you consume enough energy from food.

Adding sports for weight loss

It is not just a low body weight that reduces the chances of pregnancy, but also a high body weight: in women who are very overweight and have a body mass index (BMI) between 35 and 40, it is much less likely (23 to 43 percent) that they become pregnant than in women with a BMI of less than 29. As a guide: the "normal weight" is a BMI between 19 and 25. 

If the BMI is too high, the body produces too much insulin. This can disturb the hormonal balance and prevent the egg cell from developing normally. Women whose BMI is over 25 and who want to get pregnant are well advised to lose weight. The best way to do this in the long term is to change your diet – and add more exercise.