ACOG/SMFM released a new practice bulletin (August 2020) that addresses prenatal screening for fetal chromosomal anomalies. The guidance clearly states that both aneuploidy screening and diagnostic testing “should be discussed and offered to all patients regardless of maternal age or risk for chromosomal abnormality”
NIPS is a blood test that utilizes cell-free DNA technology (cfDNA) to predict the risk for fetal genetic disorders during pregnancy. In 2011, NIPS was introduced as a screen for T21 (trisomy 21 or Down syndrome). Today, NIPS cover the most common aneuploidies (T21, T13 and T18), as well as sex chromosomes and may also include some microdeletions and single gene genetic disorders
The preferred nomenclature is NIPS (‘S’ for screening) to emphasize that this test is used for screening only and not diagnostic. Cell-free DNA (cfDNA) is also commonly used with an understanding that the DNA is derived from placenta and not the fetus. NIPS utilizes next generation sequencing and bioinformatics algorithms to look at the DNA fragments in the mother and fetus, as a way of determining the likelihood of certain genetic conditions in the fetus. While there are multiple panels available, there is consensus regarding the clinical utility of NIPS screening for T13, T18 and T21. Patient education, especially around the concept of positive predictive value (PPV) is a priority. Calculator tools are available from professional societies (see ‘Learn More – Primary Sources’ below) or ideally laboratories should be able to provide obstetric professionals with real world test performance results.
Note: NIPS is a screening test and not diagnostic | Regardless of PPV, screen positive results require patients be offered invasive diagnostic testing to confirm results
Follow-Up for ‘No Call Result’
Note: It is preferred that the laboratory report the fetal fraction
In addition, the ACMG
Laboratory requisitions and pretest counseling information should specify the DR, SPEC, PPV, and NPV of each CNV screened. This material should state whether PPV and NPV are modeled or derived from clinical utility studies (natural population or sample with known prevalence).
Single Gene and NIPS
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