In 1990, the National Institutes of Health (NIH) proposed diagnostic criteria for PCOS, including hyperandrogenemia (biochemical hyperandrogenemia or hirsutism), scanty menstruation or amenorrhea. 2003, the Rotterdam Consensus on PCOS expanded the NIH’s diagnostic criteria by adding ultrasound to diagnose PCOS. In 2006, the Androgen Excess Society (AES) reviewed the previous diagnostic criteria and suggested that hyperandrogenemia is a necessary condition for the diagnosis of PCOS, along with ovarian dysfunction and/or polycystic ovaries on ultrasound. All of the above diagnostic criteria require the exclusion of other endocrine disorders. The prevalence of PCOS varies depending on the diagnostic criteria used. According to the NIH criteria, the prevalence of PCOS is about 6% – 10% worldwide, but if the Rotterdam or AES criteria are used, the prevalence of PCOS is significantly higher and is about 15% – 18% in white people. Insulin resistance is prevalent in women with PCOS, with an incidence of 50% – 80%. Insulin resistance is mainly manifested by hyperinsulinemia and abnormal insulin receptor signaling pathway, which is closely related to hyperandrogenemia and ovulatory dysfunction in PCOS, involving major tissues and organs such as ovaries, adrenal glands, fat, pituitary gland and liver. First, hyperinsulinemia inhibits the synthesis of hepatic sex hormone-binding globulin (SHBG), leading to elevated levels of circulating free androgens; this stimulates peripheral adipose tissue to convert androgens to estrone, leading to elevated estrogen levels: the elevated estrogen positively feeds back to stimulate pituitary luteinizing hormone (LH) secretion and increases the LH/follicle stimulating hormone (FSH) ratio, leading to abnormal follicle development and In addition, the increase in LH secretion will further stimulate the ovaries to secrete more testosterone, which will aggravate hyperandrogenemia. In addition to the ovaries, the adrenal glands and adipose tissue are also the main organs involved in androgen metabolism. The adrenal gland has the function of synthesizing androgens, but it does not synthesize testosterone with androgenic activity under normal conditions, while 30% of women with PCOS have adrenal hyperresponsiveness, resulting in increased synthesis of androgens. III. Assessment of insulin resistance in patients with PCOS The classic method of insulin sensitivity assessment is the in vivo glucose clamp technique, but this method is cumbersome and time-consuming and not suitable for clinical practice. we can assess insulin sensitivity by fasting glucose (FPG)/FINS ratio and oral glucose tolerance test. fpg/FINS can be used for screening and has a good dynamic correlation with insulin levels. Foreign scholars suggest that a ratio of less than 4.5 in white populations is considered to have insulin resistance. The OGTT is more sensitive than FPG/FINS for the detection of IGT. Treatment of insulin resistance in PCOS patients The treatment of insulin resistance in PCOS patients includes lifestyle changes, pharmacological and surgical treatments, which aim to reduce body weight, improve metabolic abnormalities, and restore reproductive and ovulatory functions, with specific protocols depending on individual conditions and needs. Metformin is the main glucose-lowering drug currently being used in the treatment of PCOS. Metformin inhibits hepatic glucose production mainly by acting on hepatic AMP-activated protein kinase (AMPK), but also directly increases insulin sensitivity and improves metabolic abnormalities. Metformin has no embryotoxic and teratogenic effects compared to other glucose-lowering drugs and has a better risk-benefit ratio, and therefore is used safely and effectively in women with various PCOS, including those in their reproductive years and during pregnancy. Also metformin is recommended as a first-line alternative to ovulation inducers. However, some studies have shown that metformin increases the rate of ovulation and clinical pregnancy in women with PCOS, while also increasing the rate of miscarriage. Although it reduces insulin and triglyceride levels compared to oral contraceptives, it has no significant advantage in the regulation of the menstrual cycle or in the reduction of androgen levels. Thiazolidinedione has a direct effect on improving peripheral insulin sensitivity and can be used in the treatment of women with PCOS. The preliminary use of the latest diabetes drugs such as glucagon-like peptide 1 analogs in women with PCOS has shown metformin-like effects, but further information is needed to verify their effectiveness and feasibility in patients with PCOS. Finally, for women with PCOS who are severely obese and whose lifestyles and medications cannot be improved, surgery is also an option to improve insulin resistance.