The onset of menstruation in the middle of taking dydrogesterone may be caused by incorrect way of taking the medication, failure of birth control, or the onset of menstruation. You should go to the hospital in time for ultrasound and gynecological examination, and treat the symptoms according to the examination results.1. Incorrect way of taking medication: If you miss taking the medication or stop taking it at will during the medication period, withdrawal bleeding may occur, which may be similar to menstruation. This is caused by a sudden drop in hormone levels in the body. It is necessary to visit a hospital, check ultrasound and blood tests under the guidance of a doctor, and carry out targeted treatment according to the situation. A small amount of bleeding can be observed, and if the bleeding is heavy, hemostatic drugs, such as tranexamic acid, should be taken under the guidance of a doctor. 2. Failure of birth control: If the treatment of preterm miscarriage due to progesterone deficiency is carried out with dydrogesterone tablets, vaginal bleeding similar to menstruation may occur when birth control is unsuccessful, in which case bed rest and timely access to a hospital for birth control treatment are required. 3. Menstrual flow: Some Some women may have normal menstrual flow without being affected by the drug during the period when they are taking oral dydrogesterone to regulate their menstruation. Therefore, it is necessary to stop the drug when menstruation comes, so that menstruation can come normally. If oral administration is required, it can be done in the second half of the next cycle and can help to regulate and repair the endometrium. If you want to continue to delay your menstruation and the bleeding is not particularly heavy, you can continue to take the medicine orally under the guidance of your doctor, but if the amount of menstruation becomes more and more during the oral medication, it is not recommended to take it orally again because it is not very meaningful and needs to be discontinued to avoid causing confusion in the menstrual cycle.4. Other cases: If a normal menstrual flow occurs in women with amenorrhea after taking dydrogesterone, it proves that there is hyperplasia in the endometrium If a woman with polycystic ovary syndrome has menstruation in the middle of taking dydrogesterone, it may be caused by the shedding of endometrium after supplementing dydrogesterone, which requires timely examination, regular observation and, if necessary, drug treatment under the guidance of a doctor.