0.5 Mb Array as a First-Line Prenatal Cytogenetic Test in Cases without Ultrasound Abnormalities and Its Implementation in Clinical Practice

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Using whole-genome array testing instead of karyotyping in prenatal diagnosis for all indications may be desirable because of the higher diagnostic yield and shorter reporting time. The goal of this research was finding the optimal array resolution that could replace routine prenatal karyotyping in cases without ultrasound abnormalities, for example, referred for advanced maternal age or abnormal first trimester screening. As variants of unknown clinical significance (VOUS), if reported, might complicate decision-making about continuation of pregnancy, such an optimal array resolution should have a high abnormality detection rate and reveal a minimal amount of VOUS. The array data of 465 fetuses were retrospectively evaluated with several resolution levels, and the Decipher microdeletion/microduplication syndrome list was reviewed to assess what could be theoretically missed with a lower resolution. A 0.5-Mb resolution showed a high diagnostic yield potential and significantly minimized the number of VOUS. Based on our experience, we recommend genomic SNP array as a first-tier test in prenatal diagnosis. The resolution should be chosen based on the indication. In cases of fetal ultrasound abnormalities or intrauterine fetal death (IUFD), high-resolution analysis should be done. In other cases, we advise replacing karyotyping by SNP array analysis with 0.5 Mb resolution.Based on our experience and the results presented here, we recommend performing rapid array testing as a first-tier test in all cases referred for invasive prenatal diagnosis by using the same array platform and performing high resolution analysis in cases of ultrasound abnormalities and 0.5Mb analysis for other indications. A 0.5Mb resolution shows a high diagnostic potential and significantly minimizes the number of VOUS. It can detect the well-known microdeletion syndromes including the atypical 22q11 microdeletion presented on the image.

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