It is normal for most women to experience a slight swelling and pain in the stomach before their period. Before menstruation, the pelvic cavity is filled with blood, so there will be discomfort in the lower abdomen. However, if lower abdominal pain occurs before menstruation and affects daily work and life, it is an abnormal phenomenon, probably due to chronic pelvic inflammatory disease. Before menstruation, the pelvic cavity is in a state of congestion, which aggravates the original pelvic inflammatory congestion, so the stomach pain occurs. In addition, if a patient has endometriosis, before menstruation, stomach pain may also occur, so it is recommended to do gynecological examination, ultrasound examination, and then give appropriate treatment according to the clinical cause of stomach pain.