Defining limits of survival: lethal pulmonary hypoplasia after midtrimester premature rupture of membranes.

Objective: Our purpose was to determine prospectively whether sequential ultrasonographic assessment of amniotic fluid volume (< 1 cm vertical pocket constitutes severe oligohydramnios), in conjunction with other readily available clinical data, could predict the occurrence of pulmonary hypoplasia and neonatal mortality in pregnancies complicated by second-trimester premature rupture of membranes.

Methods: Singleton pregnancies complicated by premature rupture of membranes at < 29 weeks' gestation were prospectively monitored by weekly ultrasonographic assessments. Stepwise multiple logistic regression analysis was used to determine the independent predictive value of ultrasonographically determined factors in the development of lethal pulmonary hypoplasia, neonatal mortality, and skeletal deformations.

Results: Neonatal mortality and pulmonary hypoplasia were statistically predicted by gestational age at rupture of membranes and interaction of premature rupture of membranes of > 14 days' duration with severe oligohydramnios. The occurrence of skeletal deformations was related to the interaction of duration of premature rupture of membranes and severe oligodramnios (p < 0.0001). Fetal breathing, fetal movements, and thoracic circumference/abdominal circumference ratios were not predictive of outcome.

Conclusions: Both duration of severe oligohydramnios exposure and gestational age at premature rupture of membranes were independent significant predictors of increased neonatal risk. Severe oligohydramnios > 14 days after premature rupture of membranes at < 25 weeks' gestation has a predicted neonatal mortality of > 90%.