Colour Doppler energy insonation of placental vasculature in monochorionic twins: absent arterio‐arterial anastomoses in association with twin‐to‐twin transfusion syndrome

Objective To determine in vivo whether monochorionic pregnancies complicated by twin‐to‐twin transfusion syndrome are associated with absence of haemodynamically‐compensatory arterioarterial anastomoses. Design Forty monochorionic pregnancies were prospectively recruited for an ultrasonographic survey of the chorionic plate using colour Doppler energy. Arterio‐arterial anastomoses were identified by their characteristic bidirectional interference pattern on spectral Doppler. Angioarchitecture was confirmed by postnatal injection study. Setting Fetal medicine tertiary referral centre in London. Main Outcome measures Presence of arterio‐arterial anastomoses, development of twin‐to‐twin transfusion syndrome, survival. Results Arterio‐arterial anastomoses were detected by colour Doppler energy in 21 pregnancies (53%), and there were no false positives. An arterio‐arterial anastomosis was more commonly found in unaffected (n= 28) compared to pregnancies affected by twin‐to‐twin transfusion syndrome (n= 12), both by colour Doppler energy [20/28 (71%) vs 1/12 (8%); Δ= 63%, 95% CI 40%‐86%] and by postnatal injection study [25/28 (89%) vs 3/12 (25%); Δ= 64%, 95% CI 37%‐91%]. In pregnancies in which no arterio‐arterial anastomoses were detected, a diagnosis of twin‐to‐twin transfusion syndrome was made in 58%, and the perinatal loss rate was 40%, compared with one case of twin‐to‐twin transfusion syndrome (5%) (P < 0.001) and a loss rate of 12% (P = 0.005) in pregnancies in which an arterio‐arterial anastomosis was detected. Conclusion Twin‐to‐twin transfusion syndrome is associated with an absence of functional arterio‐arterial anastomoses in vivo in monochorionic twin pregnancies. This contributes to our understanding of the pathophysiology of twin‐to‐twin transfusion syndrome and confirms ex vivo studies demonstrating that twin‐to‐twin transfusion syndrome is associated with a paucity of superficial anastomoses. Prospective studies are indicated to determine the utility of colour Doppler energy for arterio‐arterial anastomoses in predicting risk in monochorionic pregnancies.