Samples obtained from CVS and amniocentesis procedures are typically tested using the following methods:
Karyotype analysis
Karyotype can be defined as the number and appearance of chromosomes in the nucleus of a cell. Karyotype analysis involves the cytogenetic staining of the chromosomes in the specimen with subsequent microscopic analysis to determine total number and size of chromosomes, the sex, and any structural abnormalities with individual chromosomes. Giemsa dye is the most commonly used stain to identify chromosomes. Although karyotype analysis is considered the gold standard for chromosomal analysis of CVS and Amniocentesis specimens, it does have limitations on its ability to identify specific gene mutations.
Fluorescence in situ hybridization (FISH)
Fluorescent in situ hybridization (FISH) is a molecular cytogenetic technique that uses fluorescent probes that bind or hybridize to only those parts of the chromosome with a high degree of complimentary sequence. The technique detects and localizes the presence or absence of specific DNA sequences on chromosomes. The hybridization probe process is typically performed on a microscope slide and a fluorescence microscope is used to identify where the fluorescent probe is bound to the chromosomes.
FISH is an important technique in the clinical diagnosis of various chromosomal abnormalities including the detection of common fetal aneuploidies. The technique is often used in conjunction with karyotyping analysis and is a rapid way to detect most common fetal aneuploidies including trisomy 21, 18, and 13. Although FISH has high sensitivity and specificity for the detection of abnormalities associated with the targeted probe sequences, its diagnostic scope tends to have reduced sensitivity compared with conventional karyotype analysis. Therefore, FISH results are typically confirmed by routine karyotype analysis for chromosome analysis.
