Investigating the Fetal Circulation: Liver, Renal and Intracranial Vasculature

Abstract

Whilst interrogation of the umbilical artery (and vein) using Doppler has been a standard part of fetal assessment for over 20 years, the role of other vessels amenable to study has been subject to a slower development. Initial interest in other vessels concentrated on fetal assessment in conditions where fetal growth was sub-optimal, but as the use of ultrasound equipment with colour and pulsed wave Doppler has become more commonplace, so have the applications become wider. Examination of the fetal circulation now has a role in detection of aneuploidy, risk assessment in monochorionic twins, noninvasive assessment of fetal anaemia and the investigation of structural malformations. Whilst there is no indication for routine Doppler examination in obstetric ultrasound, there are many specific indications, some of which are only relevant to tertiary level scans. However, application of Doppler in the assessment of suspected anomalies is appropriate in the routine setting in many situations. The techniques for examining blood flow in different fetal vessels are essentially the same as those employed for the umbilical artery. The fetus needs to be quiescent. The direction of flow in the vessel should be as near vertical to the transducer as possible, with the sampling gate being small enough to accommodate the vessel. Angle correction is not essential for assessment of resistance, but is required for absolute velocities. Care should be taken to avoid excess pressure with the transducer, particularly on the fetal head, as this does affect blood flow.