There are two possible causes of cramping pain in the abdomen when menstruation occurs: First, primary dysmenorrhea. Primary dysmenorrhea refers to the absence of organic lesions such as uterine adnexa, and only manifests as menstrual abdominal pain during menstruation. Second, secondary dysmenorrhea, secondary dysmenorrhea is usually secondary to patients with endometriosis, which is divided into ovarian endometriosis or adenomyosis. No matter what type of endometriosis may cause dysmenorrhea, but the degree of dysmenorrhea pain is not necessarily proportional to the size of the lesion, and secondary dysmenorrhea is often progressively worse, and in severe cases, oral painkillers are even needed to relieve the pain each time.