Doppler waveform analysis of the intertwin blood flow in acardiac pregnancy: implications for pathogenesis

Objective To investigate interfetal hemodynamics in acardiac twins and the implications for pathogenesis. Design A retrospective study. Subjects All acardiac twins involved in this study were identified by B-mod e ultrasound at a teaching hospital in Taiwnn. Methods Color Doppler imaging and, in one case, color power angiography wer e used to assess umbilical blood flow between acardiac twins and their norm al co-twins. Placental anastomoses were examined by pathologists after deli very. Results In total Jive sets of acardiac twins and their normal co-twins were enrolled. Autonomous cardiac activity in the form of a contractile pocket was detected in two cases. Analysis of the pattern of the Doppler waveforms in each case enabled us to classify the type of hemodynamics into one of t hree categories: 'collision-summation', typified by a pattern of cyclic alt ernations of bidirectional flow; 'twin-pulse' which described the simultane ous recordings of true opposite constant flows wish different pulsating rat es; and the 'pump in' pattern, which indicated pulsatile flow in the revers ed direction towards the acardiac mass. In two cases we detected, we believ e for the first time, an artery-to-vein placental anastomosis between the a cardiac twin and its co-twin. The nature of the vascular connections were c onfirmed on pathological follow-up. Conclusions Our observations suggest that acardiac twins may be not only th e result of but also the cause of placental vascular anastomoses, which may involve either artery-to-artery or artery-to-vein anastomoses.