Summary: This involves the draining of excess amniotic fluid from the sac of the recipient (larger) twin. The process usually takes about an hour. It has the immediate effect of greatly reducing the maternal discomfort associated with carrying excess fluid, and can allow the pregnancy to continue more safely by reducing the risk of premature labour. More than one drainage is often required during the pregnancy.

Detail: Removal of excess amniotic fluid from the recipient twin has been, until recently, the best available treatment for twin-to-twin transfusion syndrome. The reason for its effectiveness is not completely clear, but removing the excess amniotic fluid may help decrease the risk of rupture of the membranes (PPROM) and premature labor. It may also be beneficial by relieving the pressure on the umbilical cord of the twin and thus improving blood flow between the fetus and the placenta.

Amnioreduction does not, however, treat the cause of twin-to-twin transfusion syndrome, only one of its effects. Since the fluid is likely to re-accumulate (usually within a few days to a few weeks), the procedure may have to be repeated. With each amnioreduction, the risk of bleeding or infection increases, as does the risk of injury to the membranes.

The results of repeated amnioreduction depend on how often this has to be done, and how rapidly fluid accumulates again. In general, the earlier in gestation the syndrome develops and the quicker polyhydramnios recurs after amnioreduction, the worse the outcome. At least one twin will survive in approximately 60-70% of cases. Unfortunately, the risks of severe complications in the surviving twins may be as high as 20%, and includes severe heart or brain anomalies. Neurological disability is reported in approximately 20% of long term survivors.

Septostomy: Sometimes the membrane in between the twins may be punctured at the time of amnioreduction to allow fluid to reaccumulate around the donor twin. Although this seems to reduce the number of procedures that might be necessary in any given pregnancy, there are other risks of both twins being in the one sac that also need to be considered prior to embarking on this therapy.