The right chord
complications may arise during pregnancy when a foetus has red blood cells that carry proteins inherited from the father, but the mother's red blood cells lack these proteins. Because of this mismatch between mother and foetus, antibodies produced by the mother's immune cells can destroy the foetus' red blood cells, leading to anaemia. This condition, known as maternal alloimmunization, may lead to brain damage or even the death of the foetus. When severe foetal anaemia is detected, a blood transfusion is often given to the foetus to restore red blood cells.
However, there is no widely agreed upon method of diagnosing foetal anaemia which occurs in thousands of pregnant women every year. They must undergo what is called an invasive procedure which necessitates some surgical intervention. Currently, all of those mothers must undergo a procedure called repeated cordocentesis, even though only about 10 per cent to 20 per cent of the foetuses will actually develop serious anaemia. Some physicians use amniocentesis, during which fluid that surrounds the foetus is extracted, while others rely on a procedure called cordocentesis, which involves drawing blood from the foetus. Cordocentesis carries a risk of infection, bleeding and foetal death, and also increases the likelihood that the mother develop the antibodies that cause serious foetal anaemia in the first place. In addition, all the invasive procedures carry risks. For example, 1-2 per cent of foetuses die as a result of cordocentesis alone. Moreover, it is also uncertain what is the best time to perform these procedures, and they may have to be repeated throughout pregnancy.
But in a study of 111 foetuses at risk of developing anaemia, researchers led by Giancarlo Mari, of the Yale University School of Medicine in New Haven, Connecticut, usa, report that an ultrasound scan that measures the speed of blood flowing through an artery in a foetus's head was 100 per cent effective at detecting moderate to severe anaemia. Foetuses, whose blood velocity was at least 50 per cent faster than normal, were at highest risk for anaemia. The test does not detect mild anaemia, but this is not much of a drawback, since mild anaemia usually is not treated during pregnancy, they note. The results of this study show that the ultrasound test, which involves bouncing sound waves off the foetus, can provide accurate results without putting a foetus at risk, as amniocentesis and cordocentesis do ( The New England Journal of Medicine , Vol 342, No 1).
The principle on which this method is based on is simple. The lower the level of red blood cells and the life-giving oxygen they carry, the faster the foetus's heart pumps, trying to get oxygen to the brain. The study found that foetuses in which the blood velocity was more than 1.50 times normal had either moderate or severe anaemia, necessitating a blood transfusion before the 34th week of pregnancy. The diagnosis was confirmed with cordocentosis, the current standard test for foetal anaemia. Ultrasound can detect virtually all cases of life-threatening anaemia in foetuses, sparing many pregnant women the need for a riskier surgical test, claim the authors.