Twin-to-twin transfusion syndrome (TTTS) is a condition of the placenta that can develop with identical twins who share a placenta. Blood vessels connect within the placenta and divert blood from one fetus to the other. It occurs in up to 15-20 percent of twins who share a placenta.
In TTTS, blood is shunted from one fetus to the other through blood vessel connections in a shared placenta. Over time, the recipient fetus receives too much blood, which can overload the cardiovascular system and cause too much amniotic fluid to develop. The smaller donor fetus does not get enough blood and has low amounts of amniotic fluid, which can also cause serious problems.