Source : Webster's Revised Unabridged Dictionary (1913)

Afterpains \Aft"er*pains`\, n. pl. (Med.)
   The pains which succeed childbirth, as in expelling the
   afterbirth.

Source : WordNet®

afterpains
     n : pains felt by a woman after her baby is born; associated
         with contractions of the uterus