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ISUOG practice guidelines (updated): use of Doppler velocimetry in obstetrics
WHY THE STUDY WAS PERFORMED
The study provides a practice guideline on the use of Doppler in ultrasound to assess the fetoplacental circulation of a pregnancy. The study aims to guide the ultrasound user on pulsed Doppler ultrasound and its different applications including spectral, colour flow, and power Doppler. The use of the techniques of Doppler ultrasound defined in the study aims to increase reproducibility and minimize technical errors that arise throughout the scan. The guideline also recognises the significance of not exposing the fetus unnecessarily or for a prolonged period, particularly in the 1st trimester.
HOW THE STUDY WAS PERFORMED
The authors describe commonly used techniques and principles of Doppler ultrasound in obstetric imaging acknowledging solid scientific literature. The authors provided the grade of recommendation used in the guideline to ensure strong scientific evidence was used.
WHAT THE STUDY FOUND
When assessing a pregnancy using Doppler ultrasound the ultrasound machine must be able to perform colour Doppler and spectral wave analysis as well as calculate the maximum velocity. In addition to this, the machine should be able to calculate the peak systolic velocity (PSV), the end diastolic velocity (EDV), time average maximum velocity, the resistive index (RI) and pulsatility index (PI) of a vessel.
Samples of vessels should be acquired whilst the fetus is still and not breathing. Colour mapping can assist the user in identifying vessels and guide where to position the sample, however not required. Ideally the angle of insonation should be as close to zero as possible without angle correction. The greater the angle of insonation, the greater the error in velocity. Doppler settings should be adjusted for optimization. This includes the wall filter (50-60MHz), PRF (low enough to enable visualization of the vessel) and appropriate sweep speed. Multiple samples should be obtained to prove reproducibility but not averaged.
Uterine artery Doppler waveforms are obtained transabdominally by showing the mid sagittal plane of the uterus with the cervix in view and moving laterally till the uterine arteries are seen at the paracervical plexus. The uterine artery should be seen ascending cranially as it goes into the uterine body. Measurements should be taken prior to the main uterine artery branching into arcuate arteries, where the PSC is >60cm/sec.
There is great variance of Doppler flows amongst the umbilical artery between the fetus and the placenta with the velocity at its highest at the fetal end of the umbilical cord. Measurements and samples of the umbilical artery should be obtained in a free loop to ensure consistency. Multiple measurements can also be taken at different locations along the cord to show reproducibility and consistency.
REVIEWED BY Sophie O’Brien ASA SIG Women’s Health
REFERENCE Bhide A, Acharya G, Baschat A, Bilardo CM, Brezinka C, Cafici D, Ebbing C, Hernandez-Andrade E, Kalache K, Kingdom J, Kiserud T, Kumar S, Lee W, Lees C, Leung KY, Malinger G, Mari G, Prefumo F, Sepulveda W, Trudinger B. ISUOG Practice Guidelines (updated): use of Doppler velocimetry in obstetrics. Ultrasound Obstet Gynecol 2021; 58: 331–339.
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The Middle Cerebral Artery (MCA) is visualised in a transverse plane of the mid brain caudal to the transthalmic plane as it arises from the Circle of Willis. Sampling of the MCA should take place in the proximal 3rd of the vessel close to its origin. Between 3 and 10 consecutive waveforms is recommended. Whilst measuring PSV with a manual trace is acceptable, autotrace is preferred when calculating the PI and RI.
Ductus venosus (DV) is seen by connecting the umbilical vein to the IVC in the abdomen using either a transverse or a longitudinal plane however, sampling is best in the mid sagittal plane. Colour mapping of the DV demonstrates a high velocity vessel. The waveform varies, usually triphasic, although biphasic waveforms have been seen in healthy fetuses.
RELEVANCE TO CLINICAL PRACTICE
Doppler is an integral part of assessing a fetus and is a technical aspect of our role as a sonographer. Up to date guidelines provide sonographers with the tools to accurately assess the fetus and ensure the wellbeing of a pregnancy. n
