If the menstrual flow suddenly becomes low, the following causes must be excluded clinically. 1. Exclude the possibility of ectopic pregnancy. Because some patients with ectopic pregnancy often show a sudden decrease in menstrual flow, patients tend to think that it is a decrease in menstrual flow rather than pregnancy, so they often ignore this situation. It is recommended to do a blood HCG test; 2. Exclude the possibility of pregnancy with preterm abortion. Due to insufficient hormone levels in the body, even if pregnancy is present, vaginal bleeding can occur clinically due to insufficient progesterone. Therefore, in addition to ultrasound examination, blood should be drawn to check the blood HCG and progesterone in clinical practice; 3. Exclude the possibility of ovarian function decline. It is recommended to draw blood to check sex hormone six. 4. Clinically, we should exclude the decrease of menstrual flow due to incomplete adhesion of endometrium caused by abortion. Therefore, for the sudden decrease of menstrual flow, a detailed clinical examination should be done.