Why must a woman have stomach pain during menstruation?

Don't have to. In primary dysmenorrhoea, the uterus works too hard to dislodge its lining and the resulting contractions and associated ischaemia (reduced blood flow) cause pain. The hormone-like compounds that prompt these contractions are prostaglandins. Women with dysmenorrhoea tend to have raised levels of prostaglandins, which cause more intense contractions of the uterus than normal.

Related Questions

What causes stomach pain during menstruation?

Well.... The uterus and adjacent organs are full of nerves. During your period you might have small contraction while expelling blood, this might cause discomfort. Read more...