Understanding Twin Anaemia-Polycythaemia Sequence (TAPS)

Understanding twin anaemia-polycythaemia sequence (TAPS)

Twin anaemia-polycythaemia sequence, or TAPS, is a rare but serious complication in pregnancies where your babies share one placenta, called monochorionic pregnancies. It happens in around three to five % of these pregnancies and can develop on its own or after laser treatment for twin-to-twin transfusion syndrome.

To understand TAPS, it helps to look at what happens to the blood. Anaemia means not having enough red blood cells, which carry haemoglobin. Haemoglobin is the substance that transports oxygen around the body. Polycythaemia is the opposite, where there are too many red blood cells in circulation.

In a pregnancy with twins, triplets or more sharing a placenta, tiny blood vessels can form between your babies. In TAPS, these vessels allow blood to move slowly from one baby to the other. Over time, one baby becomes anaemic while the other becomes polycythaemic. This imbalance makes both babies’ hearts work harder than they should.

Unlike twin-to-twin transfusion syndrome, TAPS usually does not cause big changes in the amount of amniotic fluid around each baby. This makes it harder to spot without detailed scans, so regular monitoring is essential.

How TAPS affects twins, triplets or more

TAPS only affects pregnancies where at least two babies share a single placenta. If each baby has their own placenta, known as dichorionic twins or trichorionic triplets, they are not at risk of TAPS.

Most of the time, you will not feel any clear symptoms yourself. TAPS is usually picked up on scans rather than through changes you notice in your body. This is why it is so important to attend every appointment and scan you are offered.

Your team will often use doppler scans to look for TAPS. A doppler scan measures how fast blood is flowing through your babies’ blood vessels, especially in the middle cerebral artery in the 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 shows one baby has faster blood flow and the other has slower blood flow, TAPS may be diagnosed. Sometimes TAPS is only confirmed after birth, by checking your babies’ blood and examining the placenta for tiny vessel connections.

If TAPS is not treated, both babies are at risk. The anaemic baby works harder to pump enough oxygen around the body. The polycythaemic baby is at risk of blood clots, called thrombosis, and heart strain because the blood is thicker. Once diagnosed, TAPS is graded into five stages, from mild to very severe, which helps guide treatment.

Monitoring and treatment options for TAPS

Because TAPS is rare, you should be referred to a specialist fetal medicine unit with experience in complications of twin and triplet pregnancies.

You can expect to have scans at least every two weeks. These usually include growth scans and doppler scans, and your team will also measure the amniotic fluid around each baby. This helps them tell TAPS apart from twin-to-twin transfusion syndrome or other conditions.

Every pregnancy is different. Your care plan will depend on how severe TAPS is and how far along your pregnancy is. If TAPS is mild, your team may suggest close monitoring without intervention, sometimes called ‘expectant management’. If there are signs that either baby is becoming unwell, more active treatment may be recommended.

Laser ablation therapy

In this procedure, doctors find the tiny blood vessels that connect your babies and seal them to stop the abnormal blood flow. It is done under local anaesthetic or an epidural, so you are awake but the area is numb. A needle and thin hollow tube are inserted into the womb, then replaced with a small telescope, called a fetoscope, and a laser fibre. The laser seals the connecting vessels so that each baby remains attached only to their own part of the placenta through their umbilical cord.

Intra-uterine transfusion (IUT)

If the anaemic baby is very unwell, they may need a blood transfusion inside the womb. You will have a small injection of local anaesthetic to numb the skin. A fine needle is then guided by ultrasound into the womb, and blood is given directly into the anaemic baby’s umbilical cord.

Intra-uterine exchange transfusion

If the polycythaemic baby’s blood is very thick, they may need an exchange transfusion. A needle is placed into their umbilical cord, some blood is taken away, then replaced with a similar amount of saline. This helps to thin the blood and ease the strain on the heart.

Sometimes the safest option is to plan an early birth so your babies can be treated in the neonatal unit after delivery. If an early delivery is likely, you should be offered steroid injections to help your babies’ lungs mature sooner. Your doctors should discuss the timing and type of birth with you, including your right to be involved in decisions about your care.

Planning birth and finding support with TAPS

As your pregnancy continues, your team will keep reviewing the safest way for you to give birth. The decision will take into account your babies’ wellbeing, how stable TAPS is and how many weeks pregnant you are. Your team will talk through the benefits and risks of different options so you can agree a plan together.

Hearing that one or both of your babies is unwell can be frightening and overwhelming. It is normal to feel worried, upset or confused while you try to take in a lot of information. None of this is your fault, and you deserve clear explanations and kind support.

Make sure you attend all your appointments, eat as well as you can, keep moderately active if it feels comfortable and rest often. Our pregnancy tracker (LINK - antenatal care checklist) can help you keep on top of the appointments and tests you should expect during pregnancy. You can also access specialist advice at TAPS Support, which can help you feel less alone with your diagnosis.

If you notice any new symptoms, or if something simply does not feel right, contact your midwife, doctor or maternity triage straight away. Asking for help early means your team can check you and your babies and offer the best possible care at every stage.