what is Twin Anemia Polycythemia Sequence?
From the National Organization of Rare Diseases (NORD) website:
Twin anemia polycythemia sequence (TAPS) is a rare but severe complication in identical twin pregnancies that share a single placenta (monochorionic). TAPS is caused by an imbalance in red blood cells exchanged between the twins through tiny placental blood circulations (anastomoses). This leads to too few red blood cells (anemia) in the donor twin and too many red blood cells (polycythemia) in the recipient twin. TAPS was first described in 2006,1 and being a relatively “new” disease; it is sometimes confused with the better-known twin-to-twin transfusion syndrome (TTTS).
However, TAPS is a separate disease with characteristic pathogenesis, diagnostic criteria, classification system, and outcome.
TAPS is a chronic and slow imbalance in blood flow between the babies, happening at any time during the pregnancy. It causes chronic anemia and polycythemia without an imbalance in the amniotic fluid between the twins, a characteristic of TTTS that often leads to maternal symptoms due to the rapid growth of the mother’s stomach.
Unlike TTTS, TAPS has no physical symptoms due to no fluid differences in the babies and often remains undiagnosed. This is why Doppler ultrasound measurements on the mid-cerebral artery are vital during pregnancy, as this is the only reliable way to detect TAPS.
Treatment options for TAPS before birth include expectant management ( “watch and wait”), premature delivery, intrauterine transfusion with or without partial exchange transfusion, laser surgery, and in very severe cases, selective reduction of the pregnancy.
The best management option is currently still unknown. The management and outcome in TAPS can vary in severity from case to case, depending upon when during pregnancy the syndrome occurs, when a diagnosis is made, and what treatments are performed.