Exercise and fertility

When it comes to female fertility, it seems that the key word tends to be moderation, unless the lifestyle choices are an obvious ‘no-no’ like chain-smoking and heavy drinking!

In particular, moderation is a word that applies to dietary choices and level of exercise. It is not surprising because physical activity and diet are closely linked, in the same way that car engine performance top speed and miles per gallon are determined by the quality and quantity of fuel in the tank.

When it comes to exercise however, that analogy becomes a little too basic. This is because, as biological entities we can change many aspects of our physical performance over time with exercise. Want to run faster? Exercise can improve your time. Want to walk longer distances? Exercise will make that possible.

Exercise works by two mechanisms: enhancing strength, which is a function of muscle building and performance, and increasing speed and endurance, which is a function of aerobic efficiency. The body likes exercise even if our brains don’t, preferring instead to sit around and watch TV or stare at computer/tablet screens in our leisure time!

So can exercise improve female fertility?

The answer is not as entirely straightforward as you might think.

Firstly, let’s take a look at BMI (Body Mass Index). BMI provides a very rough measure of adiposity, the fat content of the human body by dividing one’s weight by an interpretation of one’s height. You can find your own BMI here, simply by entering in your height and weight, but there are some important exclusions. If you have high muscle and bone mass or are a weight lifter then these results will be irrelevant.

  • Obese: BMI greater than 30 (risk factor for infertility)
  • Overweight: BMI greater than 25
  • Ideal weight for pre-pregnancy: BMI between 20 and 25
  • Healthy weight (average woman): BMI between 18.5 and 25
  • Underweight: BMI under 18.5 (risk factor for infertility)

As you can see, a high BMI, indicating high adiposity or obesity is negatively associated with female fertility, with a 2008 study citing obesity as a factor for 12% of women trying to conceive. With this in mind, some countries that offer free fertility treatment in their national health systems, such as New Zealand stipulate a target BMI that must be attained before treatment commences. In New Zealand the BMI must be below 32. In other countries such stipulations have been ruled discriminatory, and still others simply leave it to the discretion of individual clinics.

Both diet and exercise play a major role in regulating BMI, but it is worth bearing in mind a couple of other considerations:

  • Too much exercise seems to be a negative factor for fertility in women with LOW BMI. A 2013 study conducted in Denmark on 3,648 women of childbearing age found that there was a relationship between vigorous physical exercise and delayed pregnancy. Therefore, the authors suggested that women with low BMI who undergo vigorous exercise consider changing their regime to one of moderate exercise if they wish to improve their chances of becoming pregnant
  • Moderate exercise, in the same study, was associated with a small increase in fertility across all groups, irrespective of BMI

Given this, some scientists suggest that the effect of exercise on fertility may be positive up to a certain level of activity, and then may become negative above that threshold level of activity.

So the best advice seems to be to be:

  • Low BMI: indulge in moderate exercise, cut back on the hours of vigorous activity, replace some of them with moderate exercise and refrain from those intense marathon runs and decathlons!
  • High BMI: gently reduce BMI with a diet approved by your health care professional and indulge in moderate exercise

What constitutes ‘moderate exercise’? Suggestions include walking, golfing, gentle swimming e.g. breaststroke, yoga, pilates, tai-chi, gardening and light dancing – try to refrain from break-dancing or a routine from Riverdance! Between 3 to 5 hours per week is usual, but aim for the upper number if you have time.

As for vigorous exercise this is supposedly fine, but don’t overdo it if you already have a good BMI score and want to be in tip-top condition for pregnancy. Vigorous exercise includes running, aerobics, hard cycling, tennis, other extreme ball games and strength building/outdoor pursuits like climbing. It appears that doing no more than 4 hours per week is optimum. Trying for a baby and Olympic Gold at the same time may not be compatible!

However, these are very much ‘rules of thumb’ and it is always much better to get advice specifically tailored to you by a health care professional with access to your records and detailed knowledge of your physical condition before embarking on an exercise programme and more importantly diet of any kind.

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