The relation between pulmonary hypoplasia and amniotic fluid volume: lessons learned from discordant urinary tract anomalies in monoamniotic twins.

BACKGROUND: Adequate amniotic fluid (AF) volume is one of several factors felt to be essential for normal lung development. Renal agenesis and urinary tract obstruction usually result in oligohydramnios and pulmonary hypoplasia. CASE: Two sets of monoamiotic twins with discordant urinary tract anomalies were seen. One twin in each set had anomalies that in a singleton or diamiotic pregnancy would likely have resulted in fetal pulmonary hypoplasia and subsequent death. However, neither of these infants had pulmonary hypoplasia. One infant is unique in being the first case reported of normal pulmonary function and survival despite the anomaly.
CONCLUSION: Adequate AF provided by a monoamniotic twin environment may prevent pulmonary hypoplasia, which usually results from oligohydramnios due to certain fetal urinary tract anomalies.