Premature Rupture of Membranes
Amniotic fluid is normally produced continuously, and after approximately 16 weeks’ gestation is pre-dominantly dependent on fetal urine production. However, passage of fluid across the fetal membranes, across the skin, and across the umbilical cord, as well as fetal saliva production and fetal pulmonary effluent, also contribute. Amniotic fluid protects against infection, fetal trauma, and umbilical cord compression. It also allows for fetal move-ment and fetal breathing, which, in turn, permits fetal lung, chest, and skeletal development. Decreased or absent amni-otic fluid can lead to compression of the umbilical cord and decreased placental blood flow. Disruption (rupture) of the fetal membranes is associated with loss of protective effects and developmental roles of amniotic fluid.
Premature rupture of membranes (PROM) is the rup-ture of the chorioamnionic membrane before the onset of labor. PROM occurs in approximately 12% of all pregnancies. PROM is associated with about 8% of term pregnancies (37 weeks or more of gestational age) and is generally fol-lowed by the onset of labor. Preterm PROM, defined asPROM that occurs before 37 weeks of gestation, is a leading cause of neonatal morbidity and mortality, and is associated with approximately 30% of preterm deliveries. PROM leading topreterm delivery is associated with neonatal complications of prematurity such as respiratory distress syndrome, intra-ventricular hemorrhage, neonatal infection, necrotizing enterocolitis, neurologic and neuromuscular dysfunction, and sepsis. The major complication of PROM is intrauterineinfection. The presence of lower genital tract infectionswith Neisseria gonorrhoeae and group B streptococcus as well as bacterial vaginosis increase the risk of intrauterine infec-tion associated with PROM. Other complications include prolapsed umbilical cord and abruptio placentae.
Consequences of preterm PROM depend on the gestational age at the time of occurrence. Midtrimester
preterm PROM (between 16 and 26 weeks of gestational age) complicates about 1% of all pregnancies. PROM that occurs early in pregnancy following midtrimester genetic amniocentesis is very likely to seal with reaccumulation of amniotic fluid. Persistent oligohydramnios at <22 weeks of gestation is associated with incomplete alveolar devel-opment and the development of pulmonary hypoplasia. Survival is likely in the 24-week to 26-week group, although the morbidities of extreme prematurity in this group of neonates are more substantial. Infants born with pulmonary hypoplasiacannot be adequately ventilated, regardless of the gestational age at birth, and soon succumb to hypoxia and barotrauma from high-pressure ventilation.