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Achieving reliable results from non-invasive prenatal testing (NIPT) requires a sufficient amount of fetal cell-free DNA (cfDNA) in the maternal plasma. Several factors can reduce the fetal fraction, potentially leading to test failure or a 'no result' report. These include: screening before 10 weeks of gestation, suboptimal sample collection or processing, maternal obesity, certain fetal anomalies (e.g., Trisomy 18, triploidy), the use of low molecular weight heparin, and pregnancies conceived via in vitro fertilization (including multiple gestations).
While cfDNA testing is the most sensitive screening option for Trisomies 21, 18, and 13, its performance can vary. The combined false positive rate for these three trisomies is 0.15%. However, for sex chromosome aneuploidies, such as Monosomy X (Turner Syndrome), the cfDNA test performance differs. The detection rate for Monosomy X can decrease to approximately 90%, while the false positive rate for cases without Turner Syndrome increases to 0.23%.
How is the Fetal DNA Test Performed Most Reliably?
While cfDNA testing is the most sensitive screening option for Trisomies 21, 18, and 13, its performance can vary. The combined false positive rate for these three trisomies is 0.15%. However, for sex chromosome aneuploidies, such as Monosomy X (Turner Syndrome), the cfDNA test performance differs. The detection rate for Monosomy X can decrease to approximately 90%, while the false positive rate for cases without Turner Syndrome increases to 0.23%.