Fetal urine production in normal twins and in twins with acute polyhydramnios.

In twelve twin pregnancies with normal amniotic fluid volume, the urine output of each twin was lower than in fetuses from singleton pregnancies, and the combined urine output of both twins was between the 50th and 95th centile for singletons. In three twin pregnancies at 21-24 weeks of gestation with acute polyhydramnios, presumed to be due to the twin-twin transfusion syndrome, the urine output of the smaller fetus was zero and that of the larger was above the 95th centile for normal singleton pregnancies. These three pregnancies were managed by repeated amniocenteses and rapid drainage of large volumes of amniotic fluid. With advancing gestation, there was a tendency for normalization of urine output in the twins.