Why is SNP-based prenatal testing supplanting US as the definitive test to distinguish chorionicity and zygosity? And how early can this test be performed?

Why is SNP-based prenatal testing supplanting US as the definitive test to distinguish chorionicity and zygosity? And how early can this test be performed?

Why is SNP-based prenatal testing supplanting US as the definitive test to distinguish chorionicity and zygosity? And how early can this test be performed?