There are many reasons for delaying menstruation for more than 20 days, which may be pregnancy, irregular menstruation, polycystic ovary syndrome, etc. Patients should consult a doctor for a clear diagnosis and follow the doctor’s instructions for observation or medication. 1. Pregnancy: If the patient is sexually active, usually has regular menstruation, but suddenly has delayed menstruation, the patient should consult a doctor in time to find out whether she is pregnant. 2. Endocrine factors: the hypothalamus-pituitary-ovary function may be imperfect in adolescent women, at this time patients do not need to worry too much, with the development of the nervous system, the symptoms will gradually reduce. Or due to the long-term use of contraceptives lead to endocrine disorders, resulting in delayed menstruation. At this time, patients can use progesterone and other drugs under the guidance of the doctor for treatment. 3. Polycystic ovary syndrome: may be due to genetic, endocrine and other factors, the patient may show irregular menstrual cycle, hairy, acne, hair loss and other symptoms, at this time the patient can be under the guidance of the doctor to use dextroprogesterone, ethinyl estradiol cyclopropylprogesterone tablets and other drugs for treatment. There may also be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.