Menstruation does not occur after ectopic pregnancy, but patients often mistake a small amount of vaginal bleeding after miscarriage or rupture of ectopic pregnancy for menstruation. Menstruation is the cyclical shedding and bleeding of the endometrium that accompanies the cyclical changes of the ovaries (once a month, with a common cycle of about 28 days); under the regulation of estrogen and progesterone 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). Ectopic pregnancy, usually referred to as tubal pregnancy, is when a fertilized egg for various reasons lays in the fallopian tube rather than in the uterine cavity. It is an abnormal pregnancy in which 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, and it causes the endometrium to change into a meconium without cyclic shedding and bleeding, so no menstruation is formed. As the embryo gradually develops and increases in size and is limited by the space of 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, irregular (sometimes intermittent), mostly after ectopic pregnancy miscarriage or ectopic pregnancy rupture, which patients mistake for menstruation. Ectopic miscarriage is usually seen in tubal jugular pregnancy (the most common type of ectopic pregnancy) at 8-12 weeks of gestation. After the death of embryonic chorionic cells due to miscarriage, the blood HCG level drops sharply, which in turn causes the withdrawal of progesterone and estrogen levels, which may lead to necrosis, peeling and shedding of the endometrium and outflow through the vagina, manifesting as a little bleeding. The rupture of ectopic pregnancy, mostly seen in the isthmus of the fallopian tube at about 6 weeks of gestation (the second most common type of ectopic pregnancy), can cause massive intra-abdominal bleeding within a short period of time after rupture because of the rich vascularity of the myometrium of the fallopian tube. A small amount of blood may flow backwards into the vagina through the fallopian tube and uterine cavity due to increased intra-abdominal pressure, resulting in vaginal bleeding, but the amount of bleeding is not proportional to the clinical presentation of the patient. In conclusion, although ectopic pregnancy is an abnormal pregnancy, the patient’s hormone levels are altered and she will not have menstruation. However, when an ectopic pregnancy miscarries or ruptures, there will be a small amount of vaginal bleeding, which can be easily mistaken by the patient for menstruation. In this case, prompt medical attention is needed because ectopic pregnancy progresses rapidly and can be life-threatening in serious cases.