VATIS UPDATE Article

According to a study by researchers at the National Institutes of Health (NIH) and other institutions in the United States, extending noninvasive prenatal screening to all 24 human chromosomes can detect genetic disorders that may explain miscarriage and abnormalities during pregnancy. Because of the way data have been analyzed, typical genomic tests performed during pregnancy have targeted extra copies of chromosomes 21, 18 and 13, but rarely evaluated all 24 chromosomes.

The study may ultimately improve the accuracy of these tests, including by explaining why some give false-positive results. Researchers analyzed DNA sequence data from nearly 90,000 samples of maternal plasma, the liquid portion of blood after all cells have been removed. Of these samples, 72,972 came from a U.S. cohort and 16,885 came from an Australian cohort. For each, researchers calculated a normalized chromosome denominator quality (NCDQ), which measures the likelihood that a sample has the standard two copies of each chromosome.

Those with an NCDQ of 50 or below were flagged for further evaluation. In the U.S. cohort, 328 (0.45%) samples were flagged and ultimately classified as abnormal. In the Australian cohort, 71 (0.42%) samples were deemed abnormal, 60 of which contained a rare trisomy. Trisomy 7 was observed most frequently in both study cohorts, followed by trisomies 15, 16 and 22. Pregnancy and other outcome data were available for 52 of the 60 cases of rare trisomies found in the Australian cohort.