Metformin is a drug used to treating diabetes mellitus type-2. During type-2 diabetes mellitus, the body has enough insulin but it is not effective due to a so called "insulin resistance". In order to compensate, insulin levels can be increased. In some way, not well-defined yet, the excess insulin causes an increased production of androgenic (male) hormones in the ovaries. Increased level sof androgenic hormones can then disturb the axis hypothalamus-pituitary gland-ovaries. The final result is stimulation of many ovarian follicles (polycystic ovaries). Only a few (or none at all) become full grown enough to ovulate and become fertilized. Without ovulation (or rare ovulations), conception is very difficult or impossible.
Metformin treats the body's insulin resistance and can help to establish ovulation. Metformin can be also combined with some other drugs like anti-estrogens (Clomifen) and gonadostimulators (FSH and LH) for this effect. This therapy needs longer periods of time to take effect (6-12 months). “In vitro” fertilization can be also used for achieving pregnancy. If medications don’t help, laparoscopic surgery is indicated (ovarian drilling).
Decreasing the body weight can also contribute for treating the insulin resistance.