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CLINICAL STUDIES
Study: Genetic sonogram increases Down syndrome detection rates
The addition of genetic sonography can increase detection
rates and maximize the accuracy of noninvasive testing for
Down syndrome during the second trimester of pregnancy, according
to a substudy of the FaSTER screening trial published in the
November edition of Obstetrics and Gynecology.
The study, which sought to estimate the effectiveness of applying
genetic sonography to modify Down syndrome screening results,
utilized data generated from the First and Second Trimester
Evaluation of Risk (FaSTER) aneuploidy screening trial, whose
participants included nearly 39,000 pregnant women. In using
this data, the authors said they were able to demonstrate that
the addition of a genetic sonogram to all modes of screening
in pregnancy allows for optimal noninvasive prenatal detection
of Down syndrome.
Kjersti Aagaard, MD, assistant professor of obstetrics and
gynecology at Baylor College of Medicine in Houston, and colleagues
screened a total of 7,842 of the nearly 39,000 pregnant women
who took part in the FaSTER trial for the study using a noninvasive
genetic sonogram, an ultrasound system that details the fetal
anatomy in the second trimester and searches for the presence
of major fetal anomalies or specific anatomic features that
might be found in a child with Down syndrome, said Aagaard.
The women were studied in 13 different locations, where a
15- to 23-week genetic sonogram was performed in the same location.
Mid-trimester Down syndrome risks were estimated for five screening
test policies: first-trimester combined, second-trimester quadruple,
and testing sequentially by integrated, stepwise or contingent
protocols, said the authors.
Noninvasive screening for Down syndrome can include an early
ultrasound to detect nuchal translucency in the fetus’ neck
tissues and series of tests for looking for biochemicals in
the mother's blood at particular points during the pregnancy,
typically the first and/or second trimesters.
Invasive screening tests, which are commonly considered to
be more definitive, include amniocentesis, the direct measurement
of chromosomal material in fetal cells found in the fluid inside
the uterus and chorionic villus sampling, an earlier means
of obtaining fetal cells from tissue found in the placenta.
Both tests carry the risk for complications and many pregnant
women hope to try to avoid these risks, said the authors.
The study saw a detection rate of Down syndrome babies as
varying from 69 percent for the genetic sonogram alone to 81
to 90 percent with the combined test and the quadruple test
seeing the same rate, 93 to 98 percent with the integrated
test, from 97 to 98 percent with the stepwise test and 95 to
97 percent with the contingent test.
Additionally, the enhanced detection rate was accompanied
by a decrease in the screening tests false-positive rates,
according to the authors.
"We did not miss a single case of Down syndrome with
our overall screening program, which included an option for
invasive testing," concluded Aagaard. "Based on our
findings, it is our expectation that this will serve as the
definitive study with which clinicians can reliably inform
women of their risk in a noninvasive fashion with currently
available technology.”
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