Doppler ultrasound is a noninvasive prenatal test that can be used to check a baby’s health in high-risk pregnancies. Providers usually use Doppler ultrasound during the last trimester, but it may be done earlier.
During Doppler ultrasound, your provider or ultrasound technician holds a plastic tool, called a transducer, against your skin to measure the blood flow in the umbilical cord and some of your baby’s blood vessels. (Regular ultrasound will show you a still image, but it cannot show the actual blood flow.) High-frequency sound waves are bounced off circulating red blood cells to project the image of the flow. This test shows if your baby is getting enough oxygen. Your provider also can listen to your baby’s heartbeat using Doppler ultrasound.
Some providers use Doppler ultrasound to check mothers with Rh disease. This is a condition where a difference between the mother’s blood and baby’s blood can cause a dangerous kind of anemia in the baby. Anemia is when the body doesn’t have enough red blood cells or the red blood cells are too small. When the condition is found early and treated, most affected babies survive. Doppler ultrasound has reduced the need for amniocentesis to monitor fetuses at risk of Rh disease.