Menstruation should stop after normal pregnancy, but women with abnormal pregnancy status such as pre-eclampsia, ectopic pregnancy, biochemical pregnancy, etc., may have vaginal bleeding with more or less blood, which is often mistaken for menstruation and needs to be identified by testing blood HCG, progesterone and gynecological ultrasound. The clinical term for the time of pregnancy is called the gestational week. For most women with regular periods, the time of pregnancy is calculated from the first day of the last menstrual period. A woman will ovulate approximately 2 weeks after her period, and conception is possible during intercourse at the time of ovulation. The sperm meets the egg to form an embryo, which travels through the fallopian tube in the mother’s body and after about 1 week travels to the uterine cavity and begins to attach to the mother’s endometrium. This is about 3 weeks after the last menstrual period, when the trophoblast cells that make up the embryo invade the blood vessels of the mother’s uterus and begin to secrete human chorionic gonadotropin, or HCG, at which time the woman can confirm pregnancy by testing the mother’s blood or urine for HCG. In a normal state, the HCG secreted by the embryo prevents the endometrium from shedding and is used to nourish the embryo, and the woman will not have her period. However, in cases such as pre-eclampsia, ectopic pregnancy and biochemical pregnancy, the trophoblast cells do not receive sufficient blood supply from the mother, which will lead to abnormal HCG secretion level and cause partial shedding of endometrium inside the uterine cavity, which will result in vaginal bleeding, and pregnant women should pay attention to this and need intervention treatment.