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.c The Associated Press
Ultrasound can detect virtually all cases of life-threatening anemia in fetuses, sparing many pregnant women the need for a riskier surgical test, according to a study in today's New England Journal of Medicine.
Serious anemia occurs in a small percentage of fetuses who inherit certain types of red blood cells from their fathers. If the mother doesn't have the same type, her immune system may form antibodies that attack the fetus's red blood cells, causing serious complications and even death in the fetus.
The study found that ultrasound was 100 percent effective at detecting moderate or severe fetal anemia.
Researchers used ultrasound to measure the speed of blood moving through the middle cerebral artery in 112 fetuses at risk for anemia.
The lower the level of red blood cells and the life-giving oxygen they carry, the faster the fetus's heart pumps, trying to get oxygen to the brain. The study found that fetuses in which the blood velocity was more than 1 1/2 times normal had either moderate or severe anemia, necessitating a blood transfusion before the 34th week of pregnancy.
The diagnosis was confirmed with the current standard test for fetal anemia: cordocentesis, which involves inserting a needle through the mother's uterus and into the umbilical cord to withdraw fetal blood.
An estimated 14,000 pregnancies in the United States each year involve a risk of fetal anemia. Currently, all of those mothers must undergo repeated cordocentesis, even though only about 10 percent to 20 percent of the fetuses will actually develop serious anemia, said Dr. Giancarlo Mari, a Yale University researcher who led the study.
Cordocentesis carries a risk of infection, bleeding and fetal death, and also increases the likelihood the mother will develop the antibodies that cause serious fetal anemia in the first place.
Ultrasound diagnosis would allow most at-risk mothers to avoid cordocentesis, which would be needed only to confirm the presence of anemia after it is detected by ultrasound, Mari said.
``This is the problem - we do invasive procedures in 80 to 90 percent of pregnant women who do not need anything,'' Mari said.
The most common type of fetal anemia occurs when the mother's blood is Rh-negative and the fetus's blood is Rh-positive. Screening for the Rh factor is nearly universal in developed countries and a simple treatment is available to prevent antibody formation.
Also see:
Ultrasonography Detects Fetal Anemia Non-Invasively
