There are two main possibilities for delayed menstruation with abdominal pain. First, women who are sexually active need to rule out the possibility of early pregnancy, which can be determined by early pregnancy test, or by blood human chorionic gonadotropin testing. If early pregnancy is confirmed, the location of the gestational sac needs to be determined promptly to rule out ectopic pregnancy. If there is a history of pre-eclampsia, early pregnancy can be treated first after confirmation of early pregnancy. If early pregnancy is ruled out, the endometrial lining is too thin to reach the thickness of menstruation due to the disturbance of estrogen and progesterone levels, or the progesterone level is insufficient due to ovulation disorder, and the endometrium cannot change from the proliferative phase to the secretory phase, which manifests as late menstruation. If the endometrium has a certain thickness by ultrasound, progesterone can be used to promote menstruation and abdominal pain is most likely a precursor to menstruation. Generally speaking, it is normal for the normal menstrual cycle to be a week early or a week late. If early pregnancy is excluded, it can be observed appropriately.