Sexual intercourse is related to menstruation. During menstruation, women should not have sex because the mucus plug of the cervix is flushed out when the vagina is bleeding, and the opening of the uterus is wide open at this time, so if they have sex, it may cause bacterial infection, which may lead to endometrial inflammation or inflammation of the fallopian tubes, which may cause pelvic inflammatory disease. The fact that sex at this time may cause contraction of the uterus will cause backflow of menstrual blood, which can enter the abdominal cavity through the fallopian tube, causing endometriosis and pelvic adhesions, which will have a serious impact on future pregnancies.