Ultrasound detects anaemia in the fetus

Haemolytic disease of the fetus can be detected accurately by using Doppler ultrasound to measure velocity of blood flow in the middle cerebral artery, the main artery supplying blood to the brain. Because ultrasound is noninvasive and safe, investigators believe this test can replace amniocentesis. Haemolytic disease of the fetus occurs when the mother carries antibodies that attack a protein called rhesus (Rh) D that may be found on the fetus' red blood cells. Usually, the mother develops these antibodies during one pregnancy and then the problem occurs during a subsequent pregnancy. A counter-antibody therapy called RhoGAM is given to the mother and is usually, but not always, successful in preventing the problem. In pregnancies complicated by so-called 'Rh alloimmunisation', fetuses can develop haemolytic anaemia, causing decreased blood viscosity, which results in high blood-flow velocities that can be detected by ultrasound. Traditionally, serial amniocentesis specimens were required, and a diagnosis of haemolytic anaemia was based on a technique called spectrophotometry to quantify bilirubin level, an indirect indicator of red cell destruction. Researchers from the University Medical Center in the Netherlands compared the results of the two methods in 165 fetuses. They found that Doppler ultrasound had greater sensitivity, specificity and accuracy for severe anaemia, than amniocentesis. Doppler ultrasound can safely replace invasive screening in the management of Rh-alloimmunised pregnancies. However, they also emphasise that the sensitivity of Doppler ultrasound is not 100 percent, even among experts with extensive experience in performing Doppler ultrasound of the fetus and managing Rh-alloimmunised pregnancies, so there are likely to be occasions when serial amniocentesis will still be required.