Large proximal intertwin vascular anastomoses as a rare cause of twin anaemia-polycythaemia sequence (TAPS): case report

Abstract

Background: Twin anaemia-polycythaemia sequence (TAPS) is a form of chronic twin-to-twin transfusion syndrome (TTTS) secondary to slow unidirectional blood flow across minuscule arteriovenous (AV) anastomoses. We present a case of presumed TAPS secondary to unusual, large, proximal anastomoses. Case report: Monochorionic diamniotic (MCDA) twins were born at 25+6 weeks gestation following intrauterine fetal demise. Ultrasound scan two weeks beforehand showed mild growth discordance (0.7%) with normal amniotic fluid volumes. At post-mortem, Twin 1 (825g) appeared pale and Twin 2 (770g) plethoric. Placental examination revealed side-by-side, fused cord insertions at the extreme placental edge, with one artery-to-artery (AA) anastomosis close to the cord insertion and one umbilical vein-to-umbilical vein (UV-UV) anastomosis within Twin 1's cord. All chorionic veins drained into Twin 1’s UV proximal to the anastomosis. Discussion: TAPS is characterised by anaemia in the donor twin and polycythaemia in the recipient twin without oligohydramnios or polyhydramnios and is typically caused by very small (<1 mm diameter) AV anastomoses. To our knowledge, this is the first reported case of TAPS associated with large AA and UV-UV anastomoses. The possibility of acute exsanguination from Twin 1 into Twin 2 following the demise of Twin 2 cannot be excluded. Reference 1. Tollenaar LSA, Slaghekke F, Lewi L, et al. Spontaneous twin anemia polycythemia sequence: diagnosis, management, and outcome in an international cohort of 249 cases. Am J Obstet Gynecol 2021; 224: 213.