The Doppler effect is a change in frequency of a wave when it interacts with a moving structure. When an ultrasound pulse is in a blood vessel, blood flow adds speed to the ultrasound pulse. Velocity and frequency are directly related. The ultrasound machine measures the frequency shift and calculates velocity. This may seem a little confusing, but it is a very good way to measure how things are moving deep inside the body (of the Mom or fetus. The left image is a one dimensional pulsed Doppler tracing from a very tiny embryo just 26 days after conception.
A really nice wrinkle for ultrasound is instead of measuring velocity along just one line path, we can sample movement all around the image, which lights up the heart and blood vessels wherever we are looking. This is very much like Radar weather Doppler for showing storm clouds moving through the sky. The bright red in the right sided image outlines the heart and great vessels in this 3/4 of an inch embryo, about 6.5 weeks after conception. This image is, by the way, one of our clinical images from 1990; there has been a lot of progress in Doppler technology and uses since then.
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The It is easy to see that the heart is beating. A Doppler pattern lets us establish the heart rate with great precision (which may be the best way to establish the age of an embryo early in pregnancy). The form of the Doppler pattern tells us a lot about how the heart is function as a pump, which is very important because pump failure is a component of embryonic demise in at least 60% of miscarriages. Our hope is that if we can identify early indications of heart failure, perhaps we can prevent those forms of miscarriage that are not associated with chromosome problems. Conversely, a 'normal' Doppler pattern is about 98+% predictive that the pregnancy will continue. We really prefer to see patienst first between 6 and 10 weeks gestational age.
This flash segment combined 2D Doppler imaging and 3D reconstruction of a segment of umbilical cord. Arteries are in red, the vein is in blue.
