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  • About Twin-to-Twin Transfusion Syndrome

  • Twin-to-twin transfusion syndrome (TTTS) occurs in pregnancies of identical twins who share a placenta (monochorionic twins). These twins most often share a balanced exchange of blood through communicating blood vessels, so that one twin will act as the "blood donor" one moment and as the "recipient" the next. TTTS occurs when one twin always donates blood to the other, creating an unbalanced exchange.

    In TTTS, the donor twin develops anemia due to ongoing blood loss to the other twin. The donor twin is often smaller because of the increased work required to pump blood for both twins, leaving this twin less energy to grow. The donor twin also produces less amniotic fluid (oligohydramnios) and may become nearly wrapped in the amniotic membrane because there is so little fluid. The donor twin is often the sicker of the two and the one at higher risk of dying in utero.

    The recipient twin is usually larger and overloaded with extra blood, increasing the risk of heart failure (hydrops). This twin produces too much amniotic fluid (polyhydramnios) because of the excess blood volume. Polyhydramnios is not only uncomfortable for the mother, but may cause premature rupture of the membranes and premature labor. The excess fluid may also cause other complications in the recipient twin, such as the retention of fluid around the lungs (pleural effusion), around the heart (pericardial effusion), in the abdomen (ascites) or under the skin (edema). TTTS can develop at any time during a pregnancy, even as early as 4 to 5 months. TTTS is most dangerous in the early stages of pregnancy when the babies are too immature to be delivered. TTTS occurs in about 20 percent of all identical twins, and puts about 6,000 babies at risk in the United States each year. It can also affect triplets and higher order pregnancies.

    Severe TTTS leads to the death of one or both twins in nearly 100 percent of all cases. The death of one twin is often followed by the death of the other, since they are connected through placental blood vessels. In addition, the few twins who survive may be severely affected by heart or brain damage.

    Find out more about TTTS

    The Fetal Treatment Program is a partnership of Hasbro Children's Hospital, Women & Infants' Hospital and The Warren Alpert Medical School of Brown University.