In 1935, Stein and Leventhal summarized four diseases, namely amenorrhea, hirsutism, obesity and infertility, which were called Stein-Leventhal syndrome (S-L syndrome). In PCOS patients, the ovary is enlarged, the white membrane is thickened, the follicles are at different stages of development, and granulosa cells are luteinized.
Obesity accounts for 30% ~ 60% of PCOS patients, and its incidence varies according to race and eating habits. In the United States, 50% of PCOS women are overweight or obese, while obese PCOS is relatively rare in other countries. Obesity in PCOS is centripetal obesity (also known as abdominal obesity), and even non-obese PCOS patients show an increase in the proportion of perivascular or omental fat distribution.