In medicine (obstetrics), a contraction is a forceful and sometimes painful motion of the uterus as part of the process of childbirth. Contractions, and labour in general, is one condition that releases the hormone oxytocin into the body. Contractions become longer as labour intensifies. Prior to actual labour, women may experience Braxton Hicks contractions, sometimes known as "false labour."
The uterus also contracts during menstruation. These contractions may be uncomfortable or even painful, but they are generally significantly less painful than contractions during labour.[citation needed]