A Dopplers ultrasound test uses reflected sound waves to see how blood flows through a blood vessel. It helps doctors assess the blood flow through major arteries and veins, such as those of the arms, legs, and neck. It can show blocked or reduced flow of blood through narrow areas in the major arteries of the neck. This problem could cause a stroke . The test also can find blood clots in leg veins (deep vein thrombosis, or DVT) that could break loose and block blood flow to the lungs. This problem is called a pulmonary embolism. During pregnancy, Doppler ultrasound may be used to look at blood flow in an unborn baby to check the baby’s health.