Doppler and Nuchal scans are both painless and non-invasive special ultrasound scans that are used to detect specific problems . Both types of scan are relatively new and they are available only at certain hospitals.
A Doppler scan is used to examine the blood flow in the baby or in the placenta. It is used to check babies who are small in relation to their due date or not growing as fast as expected. The test may also identify women at risk of developing high blood pressure. It uses a different form of high-frequency sound waves, which are processed to show special wave forms. These sound waves reflect off moving objects, particularly red blood cells moving through arteries and veins. A Doppler scan shows the speed at which these cells are travelling; this tells doctors about the flow of blood through the blood vessels, indicates whether the placenta is working properly, or if the baby is short of oxygen.
The Doppler scan has been used in obstetrics, gynecology, and many other areas of medicine for at least ten years and it has never caused any safety concerns. However, to be on the safe side, it is not used in very early pregnancy. It tends to be available only at larger hospitals with specialist units.
A Nuchal scan is an ultrasound scan in which the baby's neck is examined (see below) . It is a fairly new but safe method of early antenatal screening for Down's syndrome. Although it does not give a definitive answer, it can show at a very early stage if there is a chance that your baby has Down's. It may be the best non-invasive test available at the moment. If it shows this risk is high, you can be offered amniocentesis or CVS.