Female genital mutilation
Painful periods are common because it is very difficult for the monthly menstrual blood to get out of the tiny hole left by infibulation.  Blood can fill the vagina and uterus, and stay there without moving.  If the vagina gets completely blocked, the vagina and uterus can fill up completely with menstrual blood.  Because women with this problem do not menstruate, and blood builds up in their abdomen (making it swell), it can be confused with pregnancy.