Fetal transfusion syndrome (TTTS) is a complication that can occur as a consequence of multiple pregnancy. This disorder is characterized by the unbalanced passage of blood from one fetus to another. Specifically, the fetus that passes the blood is called the donor, while the fetus that receives the blood is called the recipient.
The incidence of FTS is about 10-15% of monochorionic pregnancies, i.e. those twin pregnancies where there is only a single shared placenta. This is 1 in every 2,000 pregnancies.