Internal ejaculation during menstruation does not usually cause pregnancy, and the probability of pregnancy is very small, less than 5%. Since most women do not ovulate during menstruation, the probability of conception is almost non-existent, and there is no need to take the morning-after pill to remedy the situation. However, during menstruation, the uterine opening is open and usually in a bleeding state, so having sex can easily cause infection of the genitourinary tract and even endometriosis, which may affect future menstruation and cause dysmenorrhea. If there are no abnormal symptoms, you can observe, but if there are symptoms of pelvic inflammatory disease such as lower abdominal pain and lumbar swelling, it is best to come to the hospital as soon as possible and treat with herbs or antibiotics as soon as possible. Try to avoid sex during menstruation, it is best to have sex more than 3 days after the menstruation is clean, and to strictly do contraceptive measures.