We all know that obesity can increase the incidence of many chronic diseases (e.g. cardiovascular disease, diabetes, etc.), and in addition, obstetric complications (e.g. gestational hypertension, gestational diabetes, etc.) are also more frequent in obese women than in normal weight women. So does obesity affect fertility? The answer is yes, obesity can reduce fertility in both men and women. When patients first come to the fertility center, they are asked about their height and weight during their medical history in order to clarify whether they are of normal weight. How to determine whether the weight is normal or not, usually we will use height and weight to calculate a ratio that is body mass index (BMI) [weight (kg) / height (cm)2], BMI between 18.5 to 24.0 kg/m2 is normal, BMI between 25 to 29.9 kg/m2 is overweight, 30 to 34.9 kg/m2 is obese, and more than 35 kg/m2 is Overweight. Obese women often have polycystic ovary syndrome (PCOS). Most of these women have abnormal lipid metabolism and insulin resistance, which clinically manifest as menstrual disorders, ovulation disorders or anovulation. Obesity also affects the quality of eggs and embryos and reduces the endometrial tolerance, resulting in infertility or failure to conceive, and the risk of embryonic abortion and miscarriage after pregnancy is higher than that of normal weight women. In addition, obesity also affects the quality of male semen. Therefore, it is very important to reduce weight, which is the basis for the follow-up treatment of infertility, and obese women should keep their mouths shut (no sugar, less oil) and legs open (more exercise) in life.