How does obesity affect fertility?

Obesity is a major contributor to multiple conditions which are associated with infertility.

Research demonstrates that women who are obese are at increased risk of infertility and subject to longer timeframes to achieve pregnancy.

In addition to reduction in fertility, obesity is also associated with an increased risk of miscarriage, regardless of the mode of conception⁵³.

Research also shows a strong link between obesity and the incidence of polycystic ovarian syndrome (PCOS).

Effects of obesity

It is believed that the effect of obesity on female fertility results from systemic changes which affect the level of sex hormones, the quality and availability of eggs, and also endometrial receptivity⁵³.

The mechanisms involved are complex and multifactorial. However, it is understood that obesity has a profound effect on both the secretion and metabolism of sex hormones.

Excess adipose secretes pro-inflammatory cytokines. These inflammatory cytokines act to increase the activity of the enzyme ‘aromatase’, which converts androgens to estrogens, resulting in increased levels of unbound oestradiol and testosterone.

This then has knock-on effects and causes hypersecretion of other sex hormones, eventually leading to impaired maturation and breakdown of ovarian follicles, and is thought to also contribute to the decrease in endometrial receptivity.

Benefits of weight loss

A systematic review and meta-analysis was conducted looking at the effectiveness of non-surgical weight loss interventions for improving fertility in people who are overweight or obese⁵⁴.

The results found that in women:

• Reduced calorie diets and exercise interventions were more likely than control interventions to result in pregnancy
• Weight loss was associated with improved ovulation
• Weight loss was associated with improved menstrual regularity
• There was no clear effect on the rate of miscarriage following weight loss