Clinician-reported chorionicity and zygosity assignment using single-nucleotide polymorphism-based cell-free DNA: Lessons learned from 55,344 twin pregnancies.

One in 20 suspected MC twin pregnancies were reported as DZ using SNP-cfDNA. Approximately 30% of 55,344 twin pregnancies were found to be MZ, including cases where chorionicity was unknown. SNP-cfDNA zygosity assessment is a useful adjunct assessment for twin pregnancies, particularly those reported as MC or without determined chorionicity.