Abstract With the increasing capabilities of non‐invasive prenatal testing (NIPT), detection of sub‐chromosomal deletions and duplications are possible.

Mosaicism ratio, or MR, is a laboratory metric that can be calculated using massively parallel sequencing data from cell-free DNA (cfDNA) screening. MR compares the amount of cfDNA present from a particular chromosome or chromosomal region to the overall fetal fraction of the specimen.

Validation study of MaterniT21 for Trisomy 21 • International collaboration of 27 prenatal diagnostic centers • 4,664 singleton pregnancies • NIPT samples collected from women high-risk for Trisomy 21 pursuing prenatal diagnostic testing • NIPT T21 Detection rate = 98.6% (209 of 212) • False positive rate = 0.2% (3/1471) • Failures/non-reportable rate = 0