For other curious women who have also wondered about the biological necessity for menstrual cramps, here’s an explanation from the FDA :
… is a result of the normal production of prostaglandins by cells in the lining of the uterus. The lining of the uterus–which has built up and thickened during the early stages of the menstrual cycle–breaks up and is sloughed off at the end of the cycle and releases prostaglandins…
The prostaglandins, in turn, make the uterus contract more strongly than at any other time of the cycle. They can even cause it to contract so much that the blood supply is cut off temporarily, depriving the uterine muscle of oxygen and thus causing pain. Women who suffer painful contractions may be producing excessive amounts of prostaglandins. Or, it may be that some women are just more sensitive to them
