This is an extract of an article written by Dr Warren Kidson, the Endocrinologist who instigated metformin treatment for women with PCOS in Australia.
The oral contraceptive pill:
For many years the oral contraceptive pill has been standard treatment for the polycystic ovary syndrome as it reduces the amount of male hormone produced by the ovaries, improving acne and body hair growth and, at the same time, giving women regular monthly artificial menstruation. It protects the woman from the possibility of developing cancer of the lining of the womb. However, recent studies in Singapore and Japan have not confirmed that women with the polycystic ovary syndrome have an increased risk of developing cancer of the lining of the womb.
Unfortunately, oral contraceptives aggravate insulin resistance and probably hasten the onset of diabetes by exposing the liver to very high levels of female hormones immediately after absorption on the tablet. A 1997 study of 98,590 nurses in the USA over a long period of time revealed that type 2 diabetes was 60% more prevalent in women taking oral contraceptives! Only half of the excess cases of diabetes knew that they were diabetic. If a woman is insulin resistant with PCOS, oral contraceptives could be expected to increase the risk of diabetes by at least 100%, and possibly by 200%.
I think I got it from the Diabetes Australia website, but I'm not sure, it's saved to my harddrive now.