Confirmatory test versus screening test analyses for fetal mosaic variations; a large scale study.

Mosaic genetic anomaly is a problematic and interpretative issue in prenatal diagnosis. Conventional karyotyping, as a confirmatory test traditionally used for detecting mosaic and nonmosiac prenatal disorders. Recently Quantitative Fluorescence PCR (QF-PCR) is used for prenatal testing. We retrospectively assessed the frequency of both mosaic and nonmosaic conditions in a large-scale study and compared the clinical value of confirmatory cytogenetic analysis with QF-PCR and other screening tests. Of 6033 cases identified as abnormal conditions by sonography or protein marker screening tests, only 180 nonmosaic and 8 mosaic cases confirmed to be abnormal by confirmatory karyotyping test results. The cytogenetic analysis was correlated with other QF-PCR confirmatory test results for nonmosiac conditions but it was not comparable for mosaic cases. The cytogenetic analyses were shown to have the greatest clinical value in revealing the various mosaic conditions. The QF-PCR test is shown to be a reliable confirmatory test for nonmosaic diseases but not for mosaicism, and the screening protein marker test can weakly indicate the presence of abnormal cell lines. Moreover, older mothers (>30 years) are at greater risk for developing mosaic ova. [ABSTRACT FROM AUTHOR]