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.”