TABLE 2.

Relationship between SNP‐cfDNA zygosity and chorionicity assignment

Chorionicity recorded by provider		Results of SNP‐cfDNA
		Monozygotic (MZ)	Dizygotic (DZ)
Total cohort	55,344 (100.0%)	16,673 (30.1%)	38,671 (69.9%)
MC	6283 (11.4%)	5965 (94.9%)	318 (5.1%)
DC	28,388 (51.3%)	3927 (13.8%)	24,461 (86.2%)
Listed as “Don't know”	10,565 (19.1%)	3817 (36.1%)*	6748 (63.9%)
Left Blank	10,108 (18.3%)	2964 (29.3%)	7144 (70.7%)

Note: *p < 0.001 Percent of MZ cases compared with cases where chorionicity was specified as MC or DC.