Doppler flow is a type of ultrasound that uses sound waves to measure the flow of blood through a blood vessel. Waveforms of the blood flow are shown on the ultrasound screen. Doppler flow studies may be used to assess blood flow in the umbilical vein and arteries, fetal brain, fetal heart, and other organs. Doppler flow is sometimes called Doppler velocimetry. A Doppler flow study is often used when a fetus has intrauterine growth restriction (IUGR), which means the fetus is smaller than normal for his or her gestational age. The waveforms may show that blood flow in the umbilical vessels of a fetus with IUGR is decreased, indicating that the fetus may not be receiving enough blood, nutrients, and oxygen from the placenta.
A specially trained doctor performs this test using a specialized ultrasound machine. The ultrasound transducer is placed on the mother's abdomen using a gel to help conduct the sound waves. The test takes several minutes to assess the flow in each blood vessel being tested. The test does not harm the fetus. If the test shows a decreased amount of blood flow, other testing may be needed.