Deep-hidden anastomoses in monochorionic twin placentae are harmless.

Objectives: Our objective was to identify the clinical consequences of deep-hidden anastomoses that occur underneath the placental surface.

Methods: Twelve placentae that underwent intrauterine laser ablation of placental anastomoses for twin-twin transfusion syndrome (TTTS) and 14 non-TTTS controls were investigated for deep-hidden anastomoses. Additionally, we investigated the inter-twin haemoglobin differences as an indicator for fetofetal transfusion. Placentae were divided into four groups: TTTS placentae without residual chorionic-plate anastomoses without deep-hidden anastomoses (group 1) and with deep-hidden anastomoses (group 2), and non-TTTS placentae with chorionic-plate anastomoses without deep-hidden anastomoses (group 3) and with deep-hidden anastomoses (group 4).

Results: Deep-hidden anastomoses were identified in 58% (7/12) of the TTTS placentae after laser surgery and in 64% (9/14) of the non-TTTS placentae. Groups 1 and 2 had equal inter-twin haemoglobin differences: medians 1.4 and 1.2 gr/dL, respectively (p = 0.48). In group 3, the median inter-twin haemoglobin difference without deep-hidden anastomoses was 2.6 gr/dL (group 3) and with deep-hidden anastomoses (group 4) it was 5.1 gr/dL (p = 0.26).

Conclusion: Both comparisons imply that deep-hidden anastomoses did not cause any additional increase in Hb difference. In conclusion, haematological and additional hemodynamical analysis show that deep-hidden anastomoses are likely to occur without any clinical consequences.