Longer distance between umbilical cord insertions is associated with spontaneous twin anemia polycythemia sequence

The aim of the study was to investigate the placental characteristics in spontaneous twin anemia polycythemia sequence.

A retrospective case-control study of spontaneous twin anemia polycythemia sequence, twin-to-twin transfusion syndrome and normal monochorionic diamniotic twin pregnancies was performed. The primary outcome was placental characteristics.

The prevalence of artery-artery anastomoses in spontaneous twin anemia polycythemia sequence and twin-to-twin transfusion syndrome groups was significantly lower than in the normal monochorionic diamniotic twin group (40.0% vs 33.3% vs 88.8%, respectively, P < .001). The total number of vascular anastomoses in the spontaneous twin anemia polycythemia sequence group (with range given in parentheses) was significantly lower than in the two control groups (3 [1-6] vs 5 [1-14] vs 6 [1-20], P = .001/<.001/.794). The number of artery-vein anastomoses in the spontaneous twin anemia polycythemia sequence was significantly lower than in the two control groups (2 [1-5] vs 4 [1-13] vs 5 [1-19], P = .011/.001/1.000). The total diameter of all vascular anastomoses was significantly smaller in the spontaneous twin anemia polycythemia sequence than in the two control groups (0.9 mm [0.3-4.7] vs 5.2 mm [0.8-24.6] vs 7.3 mm [1.0-25.1], P < .001/<.001/.104), as was the total diameter of artery-to-artery anastomoses (0.5 mm [0.3-1.3] vs 2.0 mm [0.5-11.8] vs 2.3 mm [0.7-9.7], P = .003/<.001/1.000) and the total diameter of artery-to-vein anastomoses (0.8 mm [0.3-2.1] vs 4.6 mm [0.8-15.3] vs 4.0 mm [0.2-21.8], P < .001/<.001/1.000). The ratio between the distance of the two umbilical cords insertion points and the placental maximum diameter in the spontaneous twin anemia polycythemia sequence group was significantly larger than in the two control groups (0.78 [0.49-0.99] vs 0.64 [0.32-1.00] vs 0.55 [0.05-1.00], P = .033/<.001/.138).

In spontaneous twin anemia polycythemia sequence placentas, the number of superficial vascular anastomoses is lower, their diameter is smaller and the distance between the two umbilical cord insertion points is longer.