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Is amniocentesis becoming obsolete for Down’s syndrome screening?

A recently developed test called the Materni21 allows non-invasive screening for Down’s syndrome during early pregnancy simply from a blood draw from the mother. The test is being evaluated further by clinical trials for its reliability and accuracy, but the initial studies report promising results.

It appears that fetal DNA is detectable in the maternal blood and can be used for Down’s syndrome (Trisomy 21) screening. Blood is drawn any time after 10 weeks of pregnancy and fetal DNA is purified and analyzed to determine whether it is in the expected range similar to a normal pregnancy or increased in its DNA content which would suggest Down’s syndrome. The results are available within 7-10 days and if the test is positive, chorionic villus sampling (CVS) or amniocentesis is recommended for definitive diagnosis.

Although a negative test result does not completely eliminate the risk, the initial studies suggest good correlation between positive test results and confirmation based on invasive testing such as the CVS or amniocentesis. If the test is negative, based on initial studies, the risk of Down’s syndrome is reported to be extremely low.

The indications for this test are the same indications for genetic screening during pregnancy including advanced maternal age, increased risk for Down’s syndrome based on personal or family history and increased risk based on other prenatal screening tests. The test now includes information about Trisomy 18 and 13 which are two other relatively common genetic abnormalities.

The benefit of this test is to minimize the number of invasive tests such as the CVS and amniocentesis to diagnose or rule out Down’s syndrome. Most women would prefer to get their blood drawn to find out about the health of their child rather than undergoing an invasive test which carries a small risk of miscarriage and infection (~ 1%). If verified by further studies, this new test may be combined with other screening tests during early pregnancy, eliminating the need for more invasive testing. It would be important to verify the investigational data before using this test routinely for all pregnant women to screen for Down’s syndrome and other chromosomal problems.