Having difficulties getting pregnant? You’re not alone. According to the NHS, around 1 in 7 couples may have trouble conceiving. While – in most cases – individuals have no control over the factors that contribute to infertility, research shows that some lifestyle factors can play a role. Amongst which, BMI seems to be an influence. So – how does BMI impact fertility, and what does that have to do with exercise, anyway? Continue reading to find out.
What is ‘BMI’?
Your BMI is an indirect measure of body fat percentage and is calculated by dividing your weight (in kilograms) by your height (in meters). Admittedly, using BMI as a body fat screening tool has its imperfections – other than your weight and height, it doesn’t take into consideration things like muscle mass, nutrition habits, or medical history. Nonetheless, BMI is still often considered an excellent proxy for body fat in most people.
How does body fat impact fertility?
Health experts agree that an ideal BMI pre-pregnancy is between 18.5 and 25. Anything higher or lower than that, and pregnancy rates are compromised. That’s because body fat plays a significant role in reproduction – while most people know that their ovaries produce estrogen, they don’t know that the adipose tissue (fat cells) does, too!
Body fat and natural conception
When you’re at a healthy BMI, you have a higher probability of producing an appropriate amount of estrogen. But once your BMI exceeds 25, you’re likely to have a significantly higher body fat percentage and your adipose tissue, therefore, produces more estrogen than necessary – which can prevent regular ovulation. On the flip side, when your BMI is too low (below 20), your body is unable to produce and store adequate estrogen in adipose tissue, which then adversely impacts ovulation – given that you’d need your estrogen levels to rise for the release of a mature egg from its follicle.
Influence of weight on fertility treatment success
When a couple must resort to IVF, there is a clear inverse relationship between a woman’s BMI level and pregnancy rate. So, if your BMI level is on the high side, should you delay fertility treatment and try to lose weight? The answer depends on your circumstance. Studies suggest that women with PCOS likely do meaningfully benefit from weight loss and in this case, delaying treatment in favour of making lifestyle changes may be warranted. But for those not suffering from PCOS, research mostly indicates that it’d be unwise to delay treatment, especially for women above 35 whose quality of eggs are rapidly declining.
Weight and pregnancy-related complications
Having a higher body fat has also been shown to increase the following risks during pregnancy and birth of the baby:
Obesity can impact male fertility, too
What about men’s BMI impact on fertility? Well, research shows that male fertility may also suffer when a man is overweight. Overweight men are more likely to have lower sperm counts and poorer sperm motility.
Does exercise play a role in fertility?
Exercise is a fantastic way to lose weight and, therefore, body fat when used to induce a calorie deficit. However, too much exercise can also be a bad thing – especially for women already at a low BMI. Studies show that the maintenance of an energy deficit (when fewer calories are consumed than are expended) for women with low BMI can lead to reproductive dysfunction and difficulties conceiving. Ultimately, exercise should be done appropriately, to the extent of maintaining a healthy BMI level.