Twin Anaemia-Polycythaemia Sequence is a rare complication that is specific to monochorionic pregnancies (babies who share a placenta) and occurs in 3-5 percent of these pregnancies.

Small blood vessels can form in the placenta between the babies, connecting their blood supplies, allowing a slow passage of blood from one baby to the other. This can cause the baby donating the blood (donor) to become anaemic (low blood levels), and the baby receiving the blood (recipient) to become polycythaemic (high blood levels), which can lead to overload and strain on the heart.

This can be more difficult to diagnose than TTTS, as there is no difference in the fluid volume around the babies. It can develop on its own, or after laser therapy for TTTS.

If your Obstetrician suspects your babies to have this condition, they will refer you to a specialist fetal medicine centre for further evaluation and treatment, and your babies will be monitored closely.

Treatments for severe cases such as laser therapy have been effective, but further research is still being done to determine the best treatment for this condition.

TAPS does not usually have any external symptoms, so the best thing you can do is attend all your appointments and scans where your healthcare professional can monitor you for any signs of TAPS, and advise you of the best course of action if it does develop.

The diagrams below illustrate TAPS in a twin and triplet pregnancy.

Supported by the GIFT-Surg international research project which is funded by the Wellcome Trust and EPSRC

For more information about TAPS, please visit 

Our Complications Guide is designed to help you to understand some of the conditions associated with twin, triplet and higher-order pregnancies.