Chromosomal, gestational, and neonatal outcomes of embryos classified as a mosaic by preimplantation genetic testing for aneuploidy.

Objective: To understand the clinical risks associated with the transfer of embryos classified as a mosaic using preimplantation genetic testing for aneuploidy.

Design: Analysis of data collected between 2017 and 2023.

Setting: Multicenter.

Isochromosome 21q is overrepresented among false-negative cell-free DNA prenatal screening results involving Down syndrome.

False-negative cell-free DNA (cfDNA) screening results involving Down syndrome are rare, but have high clinical impact on patients and their healthcare providers. Understanding the biology behind these results may allow for improved diagnostic follow-up and counseling. In 5 different centers offering cfDNA prenatal screening, 9 false-negative results were documented in 646 confirmed cases of trisomy 21; a false-negative rate of 1.