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Ultrasound Detects Rh-Disease Complication in Womb

It negates the need for repeated amniocentesis, study finds

THURSDAY, July 13, 2006 (HealthDay News) -- Using Doppler ultrasound tests to detect severe anemia in an unborn baby -- a complication of Rh disease -- is just as effective, if not more so, than the current standard of care, amniocentesis, a new study found.

That's good news for pregnant women with Rh disease, a blood incompatibility between mother and baby, who might have needed five or six invasive amniocentesis procedures throughout their pregnancy to monitor the baby's health.

"We can reliably detect fetal anemia with a non-invasive technique, saving women the risk of miscarriage or premature labor that comes from multiple amniocentesis," said one of the study's authors, Dr. Gareth Seaward, medical director of the labor and delivery unit at Mount Sinai Hospital and the University of Toronto.

Results of the study are published in the July 13 issue of the New England Journal of Medicine.

Rh disease generally occurs when a mother has Rh-negative blood and the father has Rh-positive blood. During pregnancy, some of the mother's blood and baby's blood inevitably mixes. If the baby has Rh-positive blood, the mother's body will begin to develop antibodies to fight against the incompatible blood. During a woman's first pregnancy, this isn't usually a problem, because the mother's body hasn't had enough time to develop antibodies, or not enough blood has mixed between mother and baby to cause the mother's immune system to respond, according to the March of Dimes.

An estimated 4,000 infants are born each year in the United States with Rh disease.

In subsequent pregnancies with an Rh-positive baby, however, this can be a potentially deadly problem if the mother isn't treated with preventive medication that stops the body's immune response to the positive blood cells. If a mother's body has developed antibodies to Rh-positive blood, it will attempt to destroy any Rh-positive blood cells it comes in contact with. If enough fetal blood cells are destroyed, anemia, jaundice, brain damage and even death can occur.

But, by monitoring the baby's health in the womb, doctors can intervene with blood transfusions for the baby if the baby's anemia gets severe enough. Currently, the usual way this is done is through amniocentesis repeated periodically throughout a pregnancy.

But, amniocentesis is an invasive procedure that carries the risk of miscarriage, infection and more. And, in an accompanying editorial in the journal, Dr. Kenneth J. Moise Jr., with the department of obstetrics and gynecology at the University of North Carolina School of Medicine, pointed out that the amniocentesis procedure itself could make Rh disease worse by mixing the mother's and baby's blood to a greater degree.

To diagnose fetal anemia with Doppler ultrasound, doctors measure the blood flow through the unborn baby's brain. Babies with anemia have thinner blood that moves faster through the brain.

To assess whether Doppler ultrasound was as effective as amniocentesis, researchers from Europe, Canada and the United States recruited 164 pregnant women who had evidence of Rh antibodies. One woman was pregnant with twins, so the study included 165 fetuses.

The study volunteers underwent both amniocentesis and Doppler ultrasound. The researchers didn't know the outcome of the ultrasound test (given first) until after the amniocentesis was performed.

They found that Doppler ultrasonography had a sensitivity rate of 88 percent, compared to 76 percent for amniocentesis. Sensitivity refers to the number of people who actually have a condition that are positively identified. Doppler ultrasonography had a specificity of 82 percent, compared to 77 percent for amniocentesis. Specificity refers to the number of people who don't have a particular condition who are correctly diagnosed.

Overall, the study found that the accuracy of ultrasound was 85 percent, versus 76 percent for amniocentesis.

"Non-invasive ultrasound is as good, if not better, in the detection of fetal anemia than an invasive test," Seaward said. "By using it, we're picking up as many fetal anemias and not exposing the pregnancy to the miscarriage rates of multiple amniocentesis."

Moise, who is the Upjohn distinguished professor of obstetrics and gynecology, added, "There's now a better test, a more accurate test with a lot less risk."

Both doctors said they would now recommend Doppler ultrasound over amniocentesis in most cases.

Moise said that if you're pregnant and have Rh antibodies, and your doctor or hospital still only performs amniocentesis to check on your baby's health, ask to be referred to a center that's already performing Doppler ultrasounds.

He said most large medical centers are using Doppler ultrasound. But, he added, in small communities where it would take a woman a long time to get to a hospital that performs these ultrasounds, it might make sense to still have an amniocentesis.

More information

The March of Dimes has more information on Rh disease.

SOURCES: Gareth Seaward, M.D., medical director, labor and delivery unit, Mount Sinai Hospital, University of Toronto, Canada; Ken Moise, M.D., Upjohn distinguished professor of obstetrics and gynecology, University of North Carolina School of Medicine, Chapel Hill; July 13, 2006, New England Journal of Medicine
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