Noninvasive prenatal test for rare trisomies showed 5 percent confirmation rate in 64,889 pregnancies
Researchers examined genome wide noninvasive prenatal testing results from 64,889 singleton pregnancies at a single center between March 2021 and July 2024. The test flagged 112 cases as positive for rare autosomal trisomies, representing 0.17 percent of the cohort. Among 79 subjects who chose invasive diagnosis, the positive predictive value for fetal confirmation reached 5.1 percent, with four cases confirmed. When uniparental disomy and runs of homozygosity findings were included, diagnostic yield rose to 8.9 percent, adding three more cases. Follow up of 104 pregnancies found 63 uncomplicated outcomes, 34 adverse pregnancy outcomes, and 7 terminations. A sequence derived theoretical mosaicism ratio showed poor discrimination for adverse outcomes in 93 pregnancies, with an area under the curve of 0.643. A threshold of 0.63 or higher associated with adverse outcomes after adjustment, yielding an adjusted odds ratio of 3.66.
Positive screens for rare trisomies carried meaningful pregnancy risk despite low fetal confirmation rates, reinforcing that invasive testing remains necessary and that sequence parameters like theoretical mosaicism ratio should supplement, not replace, chromosome, diagnostic, ultrasound, and obstetric findings.
Written by the Genomes desk from the primary source linked above and checked against it. Research use only; not medical advice. Corrections: [email protected].