Prenatal cytogenetic and cytogenomic diagnosis

Assessing the fetal karyotype is possible through procedures, such as amniocentesis and chorionic villus sampling, which allow the isolation of cell lines that are fetal in origin. Although aneuploidies are by far the most common chromosome abnormalities that lead to birth defects, a number of structural chromosome rearrangements can be identified by standard karyotype analysis. They include translocations, inversions, and supernumerary marker chromosomes. When balanced and inherited from a normal parent, these aberrations are generally not associated with a clinical phenotype; however, when de novo in origin, they have certain empirical risks. Molecular cytogenetic technologies, such as fluorescence in situ hybridization (FISH), can help to elucidate and further define fetal chromosome abnormalities. Cytogenomic techniques, such as array comparative genomic hybridization, can examine the genome at much higher resolution than karyotyping and FISH and are currently used as additional testing when ultrasound abnormalities are present with a normal karyotype as well as follow-up to abnormal karyotypes that involve de novo aberrations and material of unknown origin.