The natural history of oligohydramnios/polyhydramnios sequence in monochorionic diamniotic twins.

Twelve patients with monochorionic diamniotic twin pregnancies complicated by oligohydramnios/polyhydramnios sequence were evaluated to determine the natural history of this syndrome. Nine patients elected to continue their pregnancies and three underwent elective termination. Six of the nine continuing pregnancies delivered viable fetuses. Four of the nine continuing pregnancies had evidence of a 'stuck' twin at less than 20 weeks' gestation, and only one yielded live newborns (25%). Three patients diagnosed with a mild case of oligohydramnios/polyhydramnios sequence underwent worsening of the syndrome with a 'stuck' twin seen only after 26 weeks: all neonates survived. Five pregnancies initially diagnosed as having a 'stuck' twin showed improvement in amniotic fluid volume, with one actually reversing, so that the previously 'stuck' twin developed polyhydramnios and the co-twin became 'stuck'. In summary, among the nine non-aborted pregnancies managed conservatively, 12 of 18 fetuses (67%) survived. When the diagnosis of 'stuck' twin was made at <or= 20 weeks, only two of eight (25%) lived. These observations suggest that the oligohydramnios/polyhydramnios sequence is a dynamic process with wide and often unpredictable fluctuations in amniotic fluid volume.