Maximum Accuracy In Down Syndrome Testing

December 11, 2009

It's always preferable that testing on pregnant women be as non-invasive as possible. The problem is that non-invasive testing is not always accurate. Now, it seems that the accuracy of non-invasive tests for Down syndrome have been improved by the use of a type of ultrasound testing known as the "genetic sonogram."

Early Ultrasound

Screening of a non-invasive nature for Down syndrome and other major chromosomal or genetic abnormalities in a developing baby involves a type of early ultrasound as well as a series of other tests. These tests are performed during either the first and/or second trimester of the pregnancy, depending on the individual clinic and its standards. It is felt that the optimal way to effect non-invasive screening is to include ultrasound testing during the latter part of the first trimester for the detection of nuchal translucency. This test measures the translucent area in the tissue that is found at the back of the baby's neck. When an abnormality is present, fluid may accumulate there causing the nuchal fold to enlarge. Nuchal translucency can only be spotted during a brief window of the pregnancy.

Noninvasive Screening

In a recent study, Dr. Kjersti Aagaard-Tillery and her colleagues screened more than 8,000 pregnant women. These expectant moms had undergone FaSTER screening for chromosomal abnormalities. FaSTER stands for First and Second Trimester Evaluation Risk. Dr. Aagaard-Tillery, who is an assistant professor of obstetrics and gynecology at Baylor College of Medicine (BCM) said, “We wanted to be able to definitively describe the detection and accuracy of noninvasive prenatal screening for the detection of Down syndrome. Using our data generated in the most comprehensive study performed to date (the FaSTER trial), we demonstrated that the addition of a genetic sonogram to all modes of screening in pregnancy allows for optimal noninvasive prenatal detection of Down syndrome.”

Invasive tests carry risks for potential complications. For this reason, many women try to avoid having those tests in an effort to protect what may very well be healthy pregnancies. For this reason, scientists have been working for several decades to improve non-invasive prenatal diagnostic screening tests.

The main focus of Aagaard-Tillery's research was to include the genetic sonogram to improve the possibility of obtaining accurate results without invasive testing. This type of sonogram is a more sophisticated kind of ultrasound that can show fetal anatomy in greater detail. During the sonogram, the technician looks for the presence of what are known as the "soft markers" of Down syndrome, including specific anatomic features or fetal anomalies associated with the syndrome.  

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