Although karyotyping remains the gold standard of chromosome analysis and is still the most frequently used genetic method in prenatal diagnosis, the most important advance in cytogenetics has been the development of fluorescent in situ hybridization (FISH) technology and quantitative fluorescent polymerase chain reaction techniques (QF-PCR).
Full karyotype analysis takes approximately two weeks from amniotic fluid or chorionic villi (Fig. 16.2). Samples are cultured until sufficient dividing cells are harvested and the metaphase chromosomes spread onto microscope slides. These chromosomes are then banded by enzyme digestion and finally analysed under the microscope. In addition to detecting numerical chromosomal abnormalities (aneuploidies), this method also detects structural rearrangements and abnormalities where the size of the aberration is greater than 3Mb. A similar technique is used for fetal blood although a much more rapid result can be obtained (within 48 hours) as cultured lymphocytes divide much more quickly than amniocytes.
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Once your pregnancy is over and done with, your baby is happily in your arms, and youre headed back home from the hospital, youll begin to realize that things have only just begun. Over the next few days, weeks, and months, youre going to increasingly notice that your entire life has changed in more ways than you could ever imagine.