With MPSS technology, millions of fragments of maternal and fetal DNA are sequenced simultaneously in a single sample of maternal plasma, which is assigned to a given chromosome region and counted in comparison with a reference standard expected of a normal individual. However, to screen for aneuploidy requires a different approach-the use of massively parallel DNA shotgun sequencing (MPSS).ĭetection of aneuploidy is more difficult than for single-gene disorders because detecting fetal trisomy must reflect quantitative differences between affected and unaffected pregnancies. A similar approach can be adapted for the detection of some single-gene disorders. In Europe, noninvasive testing is commonly used to determine fetal rhesus factor (Rh) status in RhD-negative women using real-time polymerase chain reaction (PCR) amplification. The concept of using cfDNA for prenatal diagnosis is not new cfDNA has been used successfully to determine fetal sex in pregnancies at risk for X-linked disorders by identifying the Y-chromosome signal. Maternal plasma contains small fragments of cfDNA (50 to 200 base pairs) derived from the breakdown of both maternal and fetal cells, primarily derived from the placenta. However, patients should be counseled about the limitations of cfDNA analysis, including the possibility of a false-positive or false-negative test result and the necessity of confirmatory diagnostic testing to confirm screening results. Numerous studies have validated the ability of cfDNA screening for common trisomies (13, 18 and 21) and sex chromosome abnormalities with high sensitivity and false-positive rates less than 1%. Such testing can be performed as early as 10 weeks' gestation.
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This method uses massive parallel sequencing analysis of cfDNA and was introduced into clinical practice in 2011.
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The newest screening test for aneuploidy is cfDNA analysis, sometimes referred to as noninvasive prenatal screening (NIPS). Landon MD, in Gabbe's Obstetrics: Normal and Problem Pregnancies, 2021 Cell-Free DNA Analysis