Metabolic effects of obesity on reproduction.

Obese women are characterized by similar comorbidities to men, particularly type 2 diabetes mellitus and cardiovascular diseases. Moreover, they also develop some specific problems, including fertility-related disorders and some hormone-dependent forms of cancer. The relationship between excess body fat and reproductive disturbances appears to be stronger for early-onset obesity. Early onset of obesity, particularly during adolescence, favours the development of menses irregularities, chronic oligo-anovulation and infertility in adulthood. Moreover, obesity in women can increase the risk of miscarriage and impair the outcome of assisted reproductive technologies. The main factor implicated in the association between obesity and fertility-related disorders is insulin excess, which accompanies insulin resistance. Hyperinsulinaemia may be directly responsible for the development of androgen excess, through its effects in reducing sex hormone-binding globulin synthesis and circulating concentrations, and in stimulating ovarian androgen production rates. Androgen excess, in turn, represents one of the major factors leading to altered ovarian physiology and associated ovulatory disturbances. Obesity-associated hyperleptinaemia may represent an additional factor involved in anovulation, not only through the induction of insulin resistance, but also through a direct impairment of ovarian function.