Antenatal visualization of vascular anastomoses in monochorionic twins using color Doppler sonography: the protective function of these anastomoses and the phenomenon of interference beating.

This report concerns the antenatal visualization and velocimetry of an arterioarterial and a venovenous anastomosis in a monochorionic twin pregnancy using color Doppler sonography. The phenomenon of 'interference beating' occurs when two flow velocity waveforms are superimposed in one blood vessel. This characteristic image can be generated antenatally to confirm the existence of a vascular communication. We were able to reveal these anastomoses postnatally using the dye injection technique.