Dossier: Planning a family

Does sport impair fertility?

In the 1990s it was commonly believed that sport was unhealthy for women and bad for their fertility. Is there any truth to this claim? Should women who are trying to fall pregnant avoid sport? No, but...

It’s only 50 years ago that the first woman crossed the finish line of a marathon. Kathrine Switzer ran in the Boston Marathon disguised in a woolly hat and flanked by bodyguards: women were barred from running the marathon as it was believed to be too much of a strain.

A more recent example is women ski jumpers. As late as the 1990s, the then Secretary General of the International Ski Federation said that the impact on landing could damage a woman’s uterus. Such statements are simply wrong. Sport doesn’t impair fertility. Even if you’re trying to get pregnant, you don’t have to give up exercise. It's healthy and reduces stress. On the other hand you shouldn’t train too hard if you're lacking energy. This combination can hinder or even prevent pregnancy.

Looking good above all else

Almost every women in western society has gone on a diet at least once in her lifetime. To try and look as fit and slim as possible, some women do more sport and reduce their calorie intake. After training, they tuck into a plate of salad and ignore their hunger pangs. This can be disastrous, because a lack of energy can be detrimental to fertility. It’s down to biology: during famines the body puts procreation on hold until there’s enough to eat again.

In other words, the body interprets a lack of energy as an emergency, which causes a woman’s menstrual cycle to become irregular. Studies estimate that around 60% of women who do a lot of sport are affected in this way. Most hardly notice the symptoms. This can reduce the luteal phase considerably, making it more difficult to fall pregnant. Despite having regular periods, some women may not ovulate because their oestrogen levels are too low. There isn’t enough oestrogen to trigger the chain reaction needed for ovulation. In the worst case, a woman’s periods may stop altogether,

Which is known as hypothalamic amenorrhea

and can affect very active, fit and slim women. Intensive exercise and insufficient nutrition put the body under constant strain. Many women only notice that they’re no longer menstruating when they stop taking the pill. Without a menstrual cycle it’s impossible to get pregnant. Hypothalamic amenorrhea can also lead to symptoms such as digestive problems, bone atrophy, exhaustion, low sex drive, dry hair and skin, and an increased risk of heart diseases. A high price to pay for looking good.

Better to do no sport?

Does this mean women shouldn’t do sport? It’s not sport that’s the problem, but low energy intake. In most cases, all the symptoms – from an irregular cycle to hypothalamic amenorrhea – can be reversed. Fertility can also be restored. Those affected simply have to normalise their energy balance. They should do less sport for the time being and eat more. Often it’s only a few kilograms that make the difference. As soon as your period has returned to normal, you can go back to your usual exercise routine provided you get enough energy.

Losing weight through exercise  

It’s not just being underweight that can reduce your chances of falling pregnant. Being overweight is equally problematic. Seriously overweight women with a body mass index (BMI) of between 35 and 40 and far more unlikely (23 to 43%) to get pregnant than women with a BMI of less than 29. Remember that the healthy “normal” weight range is a BMI of between 19 and 25. If your BMI is too high your body produces too much insulin, which can disrupt the hormonal balance and prevent egg cells from developing normally. Women with a BMI over 25 who want to have children are advised to lose weight. The best way to achieve this in the long term is to change your diet – and do exercise.