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Over the last few decades, prenatal diagnosis of fetal chromosomal abnormalities has relied on
conventional cytogenetic analysis of cultured amniocytes,
chorionic villi, or fetal blood. FISH on uncultured
amniocytes or chorionic villi has been added in some cases
for the rapid detection of aneuploidy in chromosomes
13, 18, 21, X and Y. In the last few years, the clinical
utility of using QF-PCR to detect common aneuploidies
has been reported by a number of investigators. These
new molecular techniques for the prenatal detection of
chromosomal aneuploidy are reviewed in more detail in a
Society of Obstetricians and Gynaecologists of Canada
technical update.1 QF-PCR is a PCR-based technique
that consists of amplifying polymorphic markers located
on the chromosomes of interest to determine the
number of copies of those chromosomes present per
cell. The advantages of QF-PCR are that it requires a
small sample and allows automation of the procedure,
providing a rapid turnaround time at a lower cost than
conventional cytogenetics. Moreover, diagnostic testing
with QF-PCR eliminates the unexpected or incidental
identification of rare chromosomal abnormalities of
uncertain significance, whereas G-banding karyotyping
can yield results with a low predictive value for abnormal
phenotype because of the detection of mosaicism
and de novo balanced rearrangements.2 Some authors
have suggested that because of its high sensitivity and
specificity for the detection of the common aneuploidies,
QF-PCR should replace conventional chromosome
analysis as the method of prenatal diagnostic testing
in pregnancies at an increased risk for fetal trisomy 18
or trisomy 21 because of maternal age or an abnormal
prenatal screening test result; conventional chromosome
analysis would continue to be used for cases determined
to be at increased risk for fetal chromosomal abnormality
because of a fetal structural anomaly detected by
ultrasound.3–5
To assess the performance of QF-PCR in detecting nonmosaic trisomy 13, 18, 21, triploidy, and sex chromosomal
aneuploidies, data were collected from the relevant
publications to answer three main questions:
1. What percentage of cases cannot be reported because
either the PCR failed or the results are inconclusive
because of maternal cell contamination?
ABBREVIATIONS
FISH fluorescence in situ hybridization
QF-PCR quantitative fluorescent poly
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