Excessive obesity can lead to infertility because obesity can lead to conditions such as elevated leptin levels and insulin resistance in women’s bodies, which can eventually lead to non-ovulation if obesity persists over time. Many women have irregular menstruation when they are fat and return to normal menstruation after losing weight because of this. Usually, we use body mass index (BMI) to determine whether a person is obese, the calculation is: body mass index (BMI) = weight (kg) / height (m) squared For example, a woman of 1.6 meters tall and weighing 50 kg, the body mass index is 50/1.62, which is approximately equal to 19.53. It is generally believed that BMI ≥ 24 is considered overweight, and BMI ≥ 28 is considered obese. Women with BMI greater than 24 should preferably control their weight under the guidance of a doctor to better facilitate pregnancy. Causes polycystic ovary syndrome Polycystic ovary syndrome is a common cause of infertility, and patients with polycystic ovary syndrome are often obese. They already have ovulation problems and obesity can aggravate their failure to ovulate. Therefore, if a patient with polycystic ovary syndrome is overweight, her doctor will recommend that she lose weight first. Many patients with polycystic ovary syndrome are able to ovulate naturally after weight loss and become pregnant naturally. Affecting the IVF process Since obesity affects natural ovulation and IVF is done with medication to promote ovulation, why do doctors still ask to lose weight before starting IVF? The reason is that obesity can affect the sensitivity of the ovulation promotion process to the medication. Specifically, obese patients need to use more ovulation-promoting drugs and longer dosing time during IVF to get similar results as normal weight patients. Reducing weight before doing IVF can not only reduce the amount of ovulation-promoting drugs used and save treatment costs, but also reduce drug-induced liver and kidney damage, which is a multi-benefit. When doing IVF, obesity may affect the quality of embryos in addition to the ovulation process, resulting in a lower rate of fertilization. This means that obese patients have an increased chance of successful pregnancy after losing weight. Obesity can affect pregnancy in every way, and overweight women should control their weight scientifically and effectively, whether they are pregnant naturally or undergoing IVF.