The natural history of isolated fetal hydrothorax.

We reviewed the prenatal course and outcome of 11 fetuses with isolated unilateral or bilateral hydro thoraces identified between 14 and 34 weeks' gestation, in the absence of invasive fetal intervention. Four of these fetuses died, three in utero and one in the newborn period. Six of seven survivors had resolution of hydrothorax before birth. Eight of the 11 fetuses had unilateral and three bilateral hydrothoraces. Six of the eight fetuses with unilateral hydrothorax survived, whereas one of the three with bilateral hydrothoraces lived. Six of the 11 pregnancies were complicated by polyhydramnios; four of these six fetuses died. One fetus was found to have trisomy 21. It is difficult to draw firm conclusions from the small number of patients in this report because of the wide range of outcomes found for the sonographic variables described. This series shows, however, a tendency to complete resolution of primary unilateral fetal hydrothorax, with good outcome, particularly in second-trimester fetuses without polyhydramnios.