What is TAPS?
Twin anemia polycythemia sequence (TAPS) is a condition that can develop in monochorionic twin pregnancies. Monochorionic twins are identical, share a single placenta and have their blood circulation connected to each other via vessels on the surface of the placenta. In healthy monochorionic twins the blood flow through these connecting vessels is balanced between the two babies.
Healthy monochorionic twins
Baby
A
Baby
B
Monochorionic twins with TAPS
Baby
A
Baby
B
TAPS occurs as a result of unbalanced blood flow. The cause of TAPS are the connecting vessels on the placenta. In TAPS, these connections extremely small and usually there are only a few of them (in some TAPS cases there is only 1 connection). Through these small connecting vessels too much blood flows from one baby (the donor) to the other (the recipient). As a result, the donor will have low counts of red blood cells and develops anemia, whereas the recipient will have high counts of red blood cells, and will develop polycythemia. In contrast to twin-twin transfusion syndrome (TTTS) there is no difference in amniotic fluid between the babies. At birth, anemic TAPS donors are pale, whereas polycythemic TAPS recipients are very red. Both anemia and polycythemia can endanger the development of the unborn baby.
TAPS can occur spontaneously in 3-5% of monochorionic twins (spontaneous TAPS). TAPS can also develop after laser surgery for TTTS, in case one or a few very small connecting vessels are missed during the procedure. This form of TAPS is called post-laser TAPS and occurs in 4-16% of TTTS twins treated with laser surgery.