Pregnancy does not lead to menstruation, but patients often mistake a small amount of vaginal bleeding after a preterm miscarriage, ectopic miscarriage or rupture for menstruation. Menstruation is the periodic shedding and bleeding of the endometrium that accompanies the cyclical changes of the ovaries; the endometrium is divided into a proliferative phase, a secretory phase, and a menstrual phase (the days we call menstruation, usually 3-5 days, which is the final result of the withdrawal of progesterone and estrogen) under the regulation of estrogen and progesterone. A large amount of HCG (human chorionic gonadotropin) is secreted by the cells of the syncytial trophoblast of the placental chorionic membrane starting 10-14 days after conception, which enables the endometrium to change into the meconium needed to maintain pregnancy, and no more cyclic shedding and bleeding occurs, so no menstruation is formed. Pre-eclampsia and ectopic pregnancy are abnormal pregnancies, but they are also part of the pregnancy category and therefore do not lead to menstruation. Pre-eclampsia occurs in the early stages of pregnancy due to luteal insufficiency or endometrial barrenness and is often characterized by irregular abdominal pain and a small amount of vaginal bleeding. In ectopic pregnancy, as the embryo gradually develops and increases in size, the space limited by the fallopian tube, about 60-80% of patients may experience vaginal bleeding in small amounts in the form of dripping, dark red or dark brown and irregular; such as ectopic pregnancy miscarriage (mostly seen in tubal jugular pregnancy at 8-12 weeks of gestation, embryonic chorionic cells die, blood HCG drops, progesterone and estrogen retreat, endometrial necrosis and shedding), or ectopic pregnancy After rupture (mostly seen in tubal isthmus pregnancies around 6 weeks of gestation with massive abdominal bleeding after rupture and a small amount of blood flowing backwards into the vagina due to increased abdominal pressure).