[Origin of the urge to press in the expulsion period]

So far, the explanation of the bearing-down pains in the expulsion phase has been unsatisfactory. It is assumed that the press reflex is caused by the pressure of the presenting part on the pelvic floor. This is in contradiction to the observation that the press reflex only appears during labour pains and may occur before the presenting part reaches the pelvic floor. In the expulsion phase, the uterine contraction tenses the ligg. cardinaliae, the vagina and the rectal wall in neighbourhood of the vagina. The tension of the rectal wall leads to an urgent need of relieving bowels, which supports the press reflex. By pressing, the woman perceives a pain relief because of a reducement of the tension of the ligg. cardinalia.