Down's Syndrome Accurately Detected in First Trimester Test

A cell-free fetal DNA test can accurately and reliably screen blood samples from pregnant women for trisomy 21 (Down's syndrome).

Down’s syndrome can be detected using a non invasive first trimester cell free fetal DNA blood test, according to findings published in Ultrasound in Obstetrics & Gynecology.

Researchers from the United Kingdom scoured databases for relevant articles assessing the clinical validation of maternal blood cell free (cf) DNA analysis, and found 37 relevant studies. The studies the researchers analyzed reported cf DNA results in relation to fetal karyotype from invasive testing or clinical outcome.

The screening test can detect more than 99 percent of Down’s syndrome cases in singleton pregnancies, with very low false positive rates. Currently, it is the best type of test. The researchers wrote that the combined total number of affected (1,051) and unaffected (21,608) pregnancies was large and the heterogeneity between the studies was low. The majority of the studies were conducted on high risk pregnancies, but there were 5 studies focused on general populations as well.

The test is also capable of screening for Edward syndrome and Patau syndrome, but the accuracy rates are not as high. Edward syndrome scores at about 96 percent while Patau syndrome is about 92 percent. The false positive rate for these syndromes is 0.26 percent, though when screening for all 3 conditions, increases to 0.35 percent. Additionally, the number of affected cases examined for all 3 syndromes was much smaller than for Down’s syndrome alone.

“Traditionally, screening for fetal aneuploidies has focused on trisomy 21 [Down’s syndrome] and, with each new method of screening introduced over the last 4 decades, the 2 objectives have been to increase the detection rates and decrease the rate of unnecessary invasive tests,” the authors concluded. “There is now conclusive evidence that cfDNA analysis of maternal blood in screening for trisomy 21 in singleton pregnancies is superior to all previous methods in achieving both of these objectives. Performance of screening in twins by cfDNA testing requires further evaluation.”