[Diurnal variations in the incidence at premature rupture of the membranes]

Among 8739 deliveries premature rupture of the membranes was noticed in 1.792 cases. The premature rupture of the membranes occurred mostly during the night. During the 8 hours of the night from 2200-0600 hours the membranes ruptured more frequently than during the 16 hours of the day. One would expect that the forewaters break more readily during the daytime because of the upright position, the orthostatic pressure and some shock phenomena. The observed lower incidence of premature rupture of the membranes during the day is explained by protective mechanism which occur like a valve in the upright position.