The causes of stomachache during menstruation are abnormal uterine contraction, uterine ischemia and hypoxia, periodic changes of sex hormones and stimulation of nerve plexus in uterine isthmus. First, abnormal uterine contraction, ischemia and hypoxia, that is, prostaglandins and thromboxanes synthesized by the endometrium have contractive effects on the uterus, resulting in increased uterine muscle tension, uncoordinated uterine contraction, and dysmenorrhea. The second is the pain caused by the stimulation of the endometrium on the sensitive nerves in the isthmus and the internal orifice of the cervix. The third reason is endocrine factor. Generally, dysmenorrhea mostly occurs in dysmenorrhea with ovulation, which is related to the changes of hormone levels in the menstrual cycle. The fourth reason is that there are adrenergic and cholinergic nerves in the uterine muscles. Generally, the norepinephrine level does not return to the level before pregnancy after delivery, which explains the reason why primary dysmenorrhea disappears after delivery. Some children may have dysmenorrhea disappear after delivery. The fifth factor is the decrease of pain threshold, that is, the pain point of people with primary dysmenorrhea may be lower and more sensitive to pain than that of ordinary postmenopausal, painless or male people.
