What is TAPS?

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What is TAPS?

TAPS stands for ‘Twin Anaemia-Polycythaemia Sequence’. This is a condition found only in monochorionic twin pregnancies. Anaemia means not having enough red blood cells (which contain haemoglobin, the red substance that carries oxygen) in the blood. 

Polycythaemia is the opposite—when there are too many red blood cells in the circulation. 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. These are smaller than the connecting blood vessels seen in TTTS. 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 its heart.

TAPS 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.

Who does TAPS affect?

TAPS is a rare condition that can affect monochorionic twins or more (with twins that share a placenta). It can occur spontaneously or following incomplete laser treatment for Twin to Twin Transfusion syndrome (see above). Small blood vessels in the placenta connecting the circulations of the two babies may allow blood to leak through from one baby (the donor) to the other (the recipient). 

What are the warning signs?

The mother rarely has symptoms from TAPS—it is something that is detected on ultrasound scan of the babies. The Doppler scan measures how fast blood is flowing through the babies’ blood vessels, in particular the Middle Cerebral Artery, one of the blood vessels in the baby’s brain. If a baby is anaemic, the blood is thinner and flows faster. If a baby is polycythaemic, the blood is thicker and flows more slowly. If the Doppler scan finds fast blood flow in one twin and slow blood flow in the other, then TAPS is diagnosed.

What are the complications?

Because it is the red blood cells that carry oxygen around the body, the anaemic twin has to try harder to pump enough blood and oxygen around the body. If the anaemia is severe, this may lead to heart failure. Because the recipient twin’s blood is thick, this can lead to blood clots (thrombosis) in the circulation; it can also lead to heart failure because the blood is harder to pump around the body. 

TAPS is usually graded into 5 different stages; Stage 1 is the mildest form while Stage 5 is the most severe.

What care should I expect during my pregnancy?

TAPS is a rare condition, so you should be cared for in a Fetal Medicine Unit with expertise in managing the complications of twin and more pregnancies. Your twins will have regular scans, at least every 1 week. The Doppler blood flow in the twins will be measured. In addition, the growth and amount of water (amniotic fluid) around the babies will be measured to distinguish TAPS from TTTS or other complications. 

What are the treatment options?

If you develop TAPS, your twins or more will be monitored regularly by ultrasound scan. If the health of either baby is affected by the TAPS, it may be necessary to deliver the babies early. If it’s too early to deliver the babies, however, other treatments may be necessary; these include laser ablation, intra-uterine transfusion and exchange transfusion.

Laser ablation therapy

Laser ablation therapy involves finding the small blood vessels connecting the twins and closing them to prevent the flow of blood from one baby to the other. The surgery is conducted under local anaesthetic or an epidural/spinal, so you should be awake and, if you wish, able to watch the procedure and your babies on an ultrasound or television screen.

The procedure begins by inserting a needle and thin hollow tube into the fluid sac of one baby. The needle is removed before all telescopes (fetoscope) with a thin laser fibre is inserted through the tube. The fetoscope finds all the blood vessels in the placenta that link the blood flow between the two babies. The laser is then used to seal these blood vessels. Each baby stays connected through its own umbilical cord to its main source of blood and nutrition; but the blood can no longer flow from one baby to the other through the placenta.

Intra-uterine transfusion

Intra-uterine transfusion (IUT) involves giving a blood transfusion to the anaemic baby while still inside the womb. You will usually be given a small injection of local anaesthetic in your abdominal wall to numb the area. Then a fine needle is inserted into the womb. The position of the needle is followed by watching it on the ultrasound scan. The needle is inserted into the anaemic baby’s umbilical cord, and the baby given a blood transfusion through the needle.

Intra-uterine exchange transfusion

The polycythaemic baby’s blood is too thick. If necessary, this can be treated by exchange transfusion. In this procedure, a needle is inserted into the polycythaemic baby’s umbilical cord, as described above. Some blood is then taken from this baby. This blood is then replaced by a similar amount of saline (salty water) effectively diluting the baby’s blood.   

What might happen to my babies?

It may be necessary to deliver the babies early because of TAPS. If this happens, the babies may need to spend some time in the neonatal unit because they are premature. If it’s too early to deliver the babies, another treatment, such as Laser surgery, intra-uterine blood transfusion +/- exchange transfusion (see above). 

How and when will my babies be born?

If the TAPS is mild, your babies may be born at the usual time, i.e. 36 weeks for twins. In this situation, vaginal birth may be possible, depending on other factors, such as the position of the babies. But if TAPS is affecting the babies’ health, it may be necessary for the babies to be born early; in this situation, Caesarean section is more likely. 

What can I do?

There is nothing active that you can do to prevent or treat TAPS. The most important thing is to make sure you attend your regular scans with the specialists who can detect TAPS if it occurs, and advise you on the best treatment.

(Source: Professor Asma Khalil and Twins Trust)