This is a competing renewal to continue our investigations of the use of molecular cytogenetic testing by array copy number analysis in prenatal diagnostic testing. We have completed a prospective blinded comparison of copy number analysis (aCNA) with standard conventional karyotyping in 4400 unselected prenatal diagnostic tests. Our work demonstrates that aCNA identifies all pathologic findings seen by karyotyping and provides significant incremental information in 2% of all patients tested.