If menstruation is usually very regular and there is an occasional occurrence of 1 menstrual period that is delayed for 16 days, the following possibilities are mainly considered: 1. Pregnancy. Women of childbearing age, especially those who are sexually active, must exclude the possibility of pregnancy after the delay of menstruation. You can determine this by checking the urine pregnancy test yourself or going to the hospital to check the blood chorionic gonadotropin.2. Episodic delayed menstruation, because heaven and man are in harmony, and the human body itself is a whole, if there is a change in the season, the weather gets colder or the mood changes are more, work and study stress is more, all these factors can affect the woman’s menstruation, so that the woman will have temporary menstrual disorders. Ultrasound is needed. If the ultrasound indicates that the thickness of the endometrium is around 1.0cm, the patient can wait for the onset of menstruation. If the endometrial thickness is around 0.8cm, progesterone can be used to promote menstruation.