Rupture of Membranes

The amniotic membranes (amnion and chorion) form a fluid-filled sac that protects the fetus throughout pregnancy. Amniotic fluid is usually alkaline, with a pH around 7.0–7.5, whereas normal vaginal secretions are acidic. That difference makes chemical testing possible, but it also creates opportunities for false-positive results when other alkaline substances contaminate the sample. Rupture of membranes means the sac has opened and fluid is escaping. Prelabor rupture of membranes (PROM) occurs before labor begins at term; preterm prelabor rupture of membranes (PPROM) occurs before labor and before 37+0 weeks. Rupture during established labor is spontaneous rupture of membranes (SROM). The time from rupture to birth is called latency. The clinical consequences depend on gestational age, the duration of rupture, the amount and character of fluid, maternal infection status, and fetal response. Once the membranes are open, organisms can ascend from the vagina into the uterine cavity. Loss of fluid also reduces the cushion around the umbilical cord, increasing the possibility of cord compression or prolapse. Earlier rupture adds the risk of prematurity.