Jc. Shih et al., Doppler waveform analysis of the intertwin blood flow in acardiac pregnancy: implications for pathogenesis, ULTRASOUN O, 14(6), 1999, pp. 375-379
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.