Noncardiac thoracic anomalies.

FHT is a rare diagnosis that may be an isolated finding or associated with multiple fetal anomalies, congenital infection or isoimmunization. The natural history of the lesion is variable. The effusion may regress spontaneously; remain stable in size; or progress to involve both sides of the chest and produce fetal hydrops, pulmonary hypoplasia, and fetal or neonatal demise. Hydrops is associated with significant fetal mortality. Antenatal decompression of the hydrothorax with pleuroamniotic shunting or thoracocentesis may result in a significant decrease in perinatal morbidity and mortality. Persistent hydrothorax can usually be treated with noninvasive measures in the newborn period.