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This is a rare complication that only affects twins who share a placenta (Monochorionic). In TTTS, a blood transfusion occurs from one twin (the ‘donor’) to the other (the ‘recipient’). The donor twin becomes smaller and may suffer anaemia, while the recipient twin is put under strain. Often the donor twin also has less amniotic fluid but the recipient has lots, which can cause the mother’s belly to become larger than would be expected. If TTTS is diagnosed, your pregnancy will be closely monitored by frequent ultrasounds to check on the babies’ growth. If necessary, you may be offered laser ablation therapy to separate the blood vessels in the placenta.

Although monochorionic monoamniotic twin and triplet pregnancies are very rare, they have a high risk of adverse pregnancy outcomes (MCMA pregnancies occur in about 1 in 10,000 pregnancies overall and triplet pregnancies occur in about 3 per 10,000 pregnancies).

This occurs after one fetus develops normally whilst the other fails to develop but there are blood vessels that form in the placenta, connecting them. This results in the normal baby pumping blood directly into the fetus that didn’t develop, which becomes an abnormal appearing mass that continues to grow (undeveloped fetus). The normal baby will eventually become tired and begin to show signs of strain.

Usually involves laser therapy, to stop the blood flowing into the undeveloped fetus.

Following the procedure, the normal baby will continue to be monitored closely. Occasionally, this is discovered later in the pregnancy, and provided the normal baby is well, you may be closely monitored without intervention.

Twin Reversed Arterial Perfusion sequence (TRAPs) is a very rare complication that is specific to monochorionic pregnancies (babies who share a placenta) and occurs in roughly 1 percent of these pregnancies.

Twin Anaemia-Polycythaemia Sequence (TAPS) 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.