What Is TAPS?

Twin Anemia Polycythemia Sequence, or TAPS as it’s better known, is a rare disease affecting twins sharing a placenta. TAPS in twins has many complications, including a high chance of neurodevelopmental impairment in donor twins, as well as deafness. There is also the potential for death and injury to babies from TAPS that is not diagnosed before birth.

What Causes TAPS In Twins?

It is caused by tiny surface connections in the placenta, less than 1mm thick. Red blood cells pass from the donor twin to the recipient twin at a rate of around 5-10 milliliters per day (that’s less than half an ounce). The transfer happens slowly, and over time, it causes the donor twin to become chronically anemic, and the recipient twin to become polycythemic. For more information on how it is diagnosed, visit here.

what is taps in twins twin anemia polycythemia sequence
This image is used with permission from Gautier Scientific Illustration and the LUMC Fetal Therapy Team and may not be used or reproduced without their permission.

Think of this like one twin having blood like rosé wine or Kool-Aid, and the other twin having blood as thick as ketchup or molasses. You can also think of TTTS as the result of a combination of too high and too low blood volume while TAPS is about too high and too low blood concentration.

Symptoms of TAPS

Unlike TTTS, what’s unique about TAPS is that it does not present with fluid imbalances or other physical symptoms. There are some recorded symptoms that can be related to TAPS, like a bright placenta on the donor twin’s side (called an echogenic placenta), an enlarged heart (cardiomegaly) also for donors, and a starry sky liver in the recipient (a liver that has bright, white spots on it in ultrasound images), but these are not required additional symptoms and often TAPS will be the only issue.

However, these are markers and they should be looked for alongside routine MCA dopplers. (14% of TAPS cases will present with nothing more than discordant MCA dopplers. )

If you look closely where the arrow is pointing, you can see a line and one side of the placenta looks much brighter than the other – this is called an echogenic placenta

Advanced TAPS

As the disease progresses, things can become worse for the donor, where the chronic anemia can lead to hydrops (large amounts of fluids building up in the baby’s tissues which causes swelling), and for the recipient, things like blood clots and heart issues from pumping around the thicker blood are a real risk.

Types of TAPS

  • Spontaneous happening in around 3-5% of monochorionic twin pregnancies
  • After laser surgery for TTTS (known as post-laser TAPS). Around 16% of TTTS cases treated by laser surgery will develop TAPS. In these cases, it is caused by incomplete cauterizing of the vessels in the placenta. It used to be thought that it was common for the donor and recipient to “switch places”, ie the TTTS donor would become the TAPS recipient, and vice versa, but research from the International TAPS Registry showed that the difference was marginal, with only 55% of cases switching roles. It really highlights that the residual anastomoses are the problem.

There are several treatment options for TAPS, including (repeat) laser surgery, expectant management, early delivery, in-utero transfusions, and selective reduction. We don’t know the best treatment for TAPS yet, but this is one of the goals of the international TAPS Trial.

Long Term Effects

For post-laser TAPS, the long-term effects are about the same as for TTTS survivors, with around an overall 9% chance of neurodevelopmental impairment equally for donors and recipients equally. For spontaneous TAPS, however, this jumps to a 31% chance of neurodevelopmental impairment and a 15% chance of deafness in donor twins. Read more on long-term effects here.

Chance Of Developing TAPS

Spontaneous TAPS happens in around 3-5% of monochorionic twins without any explanation. Post-Laser TAPS happens in around 16% of cases after laser surgery with Selective Laser, with this reduced to just 3% after Solomon Laser.

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Page last updated: 30/12/2020