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Obstetric Doppler ultrasound: Are we performing it correctly?

Introduction Over the last 20 years, Doppler ultrasound has been increasingly used for the monitoring of fetal well being in a wide variety of clinical scenarios, most commonly in the investigation of the small for gestational age (SGA) fetus and intrauterine growth restriction (IUGR). With modern ultrasound machines, obtaining Doppler signals from fetal and maternal vessels has become quick and easy. We can confidently target umbilical arteries, vessels inside the fetal skull (middle cerebral artery, MCA) and tiny vessels with diameters in the single millimetre range (ductus venosus). Doppler tests are generally only used in high-risk pregnancies and obstetricians heavily rely on the results in determining the management pathway for the mother and baby. Often the decision to deliver or continue the pregnancy is made on the basis of the Doppler results. It is therefore vital that Doppler assessments are performed correctly. And therein lies the catch. As with many ultrasound applications, things may not always be as easy as they seem. Despite a large body of literature, good training schemes and widely publicised international bestpractice guidelines to help the sonographer or sonologist, there are a number of ways that errors regularly creep into our assessments. Most of these errors fall into one of the following categories: 1 Technical acquisition errors. 2 Errors related to physiologic factors. 3 Incorrect application of measurements.