Core outcomes for twin anaemia polycythaemia sequence in Twin pregnancies

Twin anaemia polycythaemia sequence (TAPS) occurs when one of a monochorionic twin pair is anaemic and the other polycythaemic. It is usually diagnosed by the finding of discordant middle cerebral artery (MCA) Doppler peak systolic velocity (PSV) between the twins (the MCA PSV should be more than 1.5 MoM in the donor and less than 1.0 MoM in the recipient). TAPS is thought to be due to slow transfusion of blood from the donor to the recipient via minute arterial-venous anastomoses (less than 1 mm in diameter). It occurs in up to 5% of MCDA twins, but in 13% following twin-to-twin transfusion syndrome (TTTS) treated with laser ablation. Postnatally, the diagnosis of TAPS is confirmed with a difference in haemoglobin concentration of more than 8 g/dl and a reticulocyte count ratio greater than 1.7, or by identifying small vascular anastomosis (less than 1 mm in diameter) on histopathological examination of the placenta. Severe TAPS may result in intrauterine death of both twins, but mild TAPS may have excellent outcomes for both. The optimal treatment and frequency of surveillance for TAPS is not yet established.

Treatment after birth may include blood transfusion of the anaemic twin and/or partial exchange transfusion of the polycythaemic twin. It seems, however, that significant TAPS can result in cerebral damage and neurodevelopmental delay in up to 20%. Brain imaging during the third trimester (by MRI if feasible) and neurodevelopmental assessment of the twins at the age of two years are therefore recommended. The optimal management of TAPS remains uncertain.

Professor Asma Khalil, St George's University of London, UK
Professor Basky Thilaganathan, St George's University of London, UK
Dr Sanne Gordijn, University Medical Center Groningen, The Netherlands
Dr Wessel Ganzevoort, Academic Medical Center, Amsterdam, The Netherlands