Polycystic ovarian syndrome, or PCOS for short, is the leading cause of female infertility, according to the World Health Organization. This condition affects a surprising number of women of childbearing age—about 1 in 10. Even more alarming, up to 70% of affected women are undiagnosed, and the condition can lead to significant health issues such as type 3 diabetes, obesity, cardiovascular disease and endometrial cancer. Any woman who has gone through puberty can develop PCOS, no matter what her age. It's not always clear what causes PCOS or why it happens. No single test can diagnose PCOS