Type 2 diabetes and polycystic ovarian syndrome are often linked with obesity [source: Baby Med]. Approximately 80 percent of Type 2 diabetes patients are either overweight or obese, and more than half of women with PCOS fall into those categories as well [source: Obesity in America.] It's far more difficult, and sometimes impossible, for the human body to maintain a healthy blood sugar level if a person is overweight or obese. Without healthy blood sugar levels, complications begin to arise. The role of Metformin is to establish properly balanced blood sugar and insulin levels [source: Fertility Authority].
Proper blood sugar and insulin levels can help prevent or reduce cysts. When cysts are removed, menstrual cycles tend to become more regular. When menstrual cycles are more predictable, the chances of becoming pregnant increase.
Generally, Metformin is recommended for women with a Body Mass Index above 25 [source: NCCWCH]. There are instances, however, in which Metformin can improve the fertility of women who are neither overweight nor obese. That's because insulin resistance can develop even in people with average or below-average body weight. So, technically speaking, it's the issue of insulin resistance and not necessarily unhealthy body weight that has to be treated to improve the odds of becoming pregnant [source: Elsner]. A change in eating habits alone doesn't always influence fertility.
Metformin can work within days to a few months depending on the woman and her particular medical history. But it's not without its side effects. Some women choose to discontinue use of Metformin because of nausea, diarrhea and other gastrointestinal issues. In rare cases, it can also lead to lactic acidosis -- a serious condition that may be marked by extreme tiredness, a change in skin color or muscular pain [source: WebMD].