It has long been appreciated that genetic analysis of fetal or trophoblast cells in maternal blood could revolutionize prenatal diagnosis. We implemented a protocol for single circulating trophoblast (SCT) testing using positive selection by magnetic-activated cell sorting and single-cell low-coverage whole-genome sequencing to detect fetal aneuploidies and copy-number variants (CNVs) at ∼1 Mb resolution. In 95 validation cases, we identified on average 0.20 putative trophoblasts/mL, of which 55% were of high quality and scorable for both aneuploidy and CNVs. We emphasize the importance of analyzing individual cells because some cells are apoptotic, in S-phase, or otherwise of poor quality. When two or more high-quality trophoblast cells were available for singleton pregnancies, there was complete concordance between all trophoblasts unless there was evidence of confined placental mosaicism. SCT results were highly concordant with available clinical data from chorionic villus sampling (CVS) or amniocentesis procedures. Although determining the exact sensitivity and specificity will require more data, this study further supports the potential for SCT testing to become a diagnostic prenatal test.

In this exciting era of "next-gen cytogenetics," integrating genomic sequencing into the prenatal diagnostic setting is possible within an actionable time frame and can provide precise delineation of balanced chromosomal rearrangements at the nucleotide level. Given the increased risk of congenital abnormalities in newborns with de novo balanced chromosomal rearrangements, comprehensive interpretation of breakpoints could substantially improve prediction of phenotypic outcomes and support perinatal medical care. Herein, we present and evaluate sequencing results of balanced chromosomal rearrangements in ten prenatal subjects with respect to the location of regulatory chromatin domains (topologically associated domains [TADs]). The genomic material from all subjects was interpreted to be "normal" by microarray analyses, and their rearrangements would not have been detected by cell-free DNA (cfDNA) screening. The findings of our systematic approach correlate with phenotypes of both pregnancies with untoward outcomes (5/10) and with healthy newborns (3/10). Two pregnancies, one with a chromosomal aberration predicted to be of unknown clinical significance and another one predicted to be likely benign, were terminated prior to phenotype-genotype correlation (2/10). We demonstrate that the clinical interpretation of structural rearrangements should not be limited to interruption, deletion, or duplication of specific genes and should also incorporate regulatory domains of the human genome with critical ramifications for the control of gene expression. As detailed in this study, our molecular approach to both detecting and interpreting the breakpoints of structural rearrangements yields unparalleled information in comparison to other commonly used first-tier diagnostic methods, such as non-invasive cfDNA screening and microarray analysis, to provide improved genetic counseling for phenotypic outcome in the prenatal setting.