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Twins / Multiples | Twin Anaemia Polycythaemia Sequence (TAPS)

Essential Information

Twin Anaemia Polycythaemia Sequence (TAPS) can develop spontaneously in up to 5% of monochorionic twin pregnancies, it can also develop rarely after incomplete laser for TTTS. TAPS is a “first cousin” of TTTS, but the connecting blood vessels in the placenta are very tiny (usually < 0.1 mm).  A slow transfusion of blood occurs between the twins creating a difference in haemoglobin, one twin having too little haemoglobin (anaemia) and the other having too much (polycythaemia). This typically develops later in pregnancy than TTTS, and may occur alone or sometimes in combination with TTTS.  Usually there is not a marked difference in the relative volumes of amniotic fluid between the twins. There are some typical ultrasound features of TAPS, including a difference in the shading in the placenta, with the anaemic donor twin’s placenta being thicker and brighter.


TAPS is treated either by fetoscopic laser ablation of the placental anastomoses, as described above for TTTS or by serial intrauterine transfusions or by delivery.  The choice of the optimal treatment will be made on a case by case basis, depending largely on gestation, as currently there is no consensus as to which is the best treatment for TAPS.


Referral Information


  • Divergent MCA PSV (middle cerebral artery peak systolic velocities) in monochorionic twins, typically one > 1.5 MoM and the other < 0.8 MoM, often in the absence of significant amniotic fluid discordance.

Twin-twin transfusion may develop acutely so please refer urgently. Inpatient admission is approximately 24 hours. Patients will usually be asked to return for one follow-up appointment with the OFC within 48-72 hours after their surgery, but will then be referred back to their local care provider for ongoing care, ultrasound follow-up and delivery.