Characteristics and clinical consequences of bipartite monochorionic twin placentas.

OBJECTIVE: To investigate the angioarchitecture and clinical consequences of bipartite monochorionic (MC) twin placentas. METHODS: Case-control study of MC twin placentas examined at the Leiden University Medical Center (The Netherlands) and University Hospitals Leuven (Belgium). We injected all MC placentas with colored dye and studied the characteristics of bipartite placentas. In addition, we evaluated the concomitant occurrence of clinical complications including twin-to-twin transfusion syndrome (TTTS), twin anemia polycythemia sequence (TAPS) and selective fetal growth restriction (sFGR). RESULTS: Bipartite placentas were detected in 2.1 % (38/1804) of MC twin placentas. In the subgroup of MC twin placentas not treated with laser surgery, vascular anastomoses were detected in 75 % (21/28) of bipartite placentas versus 96 % (1002/1030) of non-bipartite placentas (p < 0.001). The total number of vascular anastomoses were lower in bipartite placentas (4 (IQR 0-8)) versus non-bipartite placentas (8 (IQR 5-13)) (p < 0.001). Arterio-venous (AV) anastomoses were found less often in bipartite placentas compared to non-bipartite placentas: 68 % (19/28) versus 96 % (984/1022), respectively (p < 0.001). Similarly, arterio-arterial (AA) anastomoses were detected less frequently in bipartite versus non-bipartite placentas: 50 % (14/28) versus 82 % (841/1027), respectively (p < 0.001). TTTS, TAPS and sFGR were diagnosed in 26 % (10/38), 13 % (5/38) and 5 % (2/38) of bipartite placentas, respectively. CONCLUSION: Although bipartite placentas in MC twin pregnancies are rare, the majority have vascular anastomoses and may therefore develop complications such as TTTS, TAPS or sFGR.