![]() The two most common forms of testing, karyotyping and cytogenomic single nucleotide polymorphism (SNP) microarray, are the most definitive forms of prenatal genetic testing available to assess the risk for chromosome abnormalities and copy number variants in the fetus. This testing is invasive and carries a small risk of miscarriage. Prenatal genetic diagnostic testing is used to confirm whether a fetus has certain genetic disorders before birth. This topic focuses on prenatal testing for fetal aneuploidy and neural tube defects for more information on the use of laboratory tests in carrier screening for genetic disorders, see the ARUP Consult Carrier Screening for Genetic Disorders topic. Abnormal results should be followed by confirmatory prenatal genetic diagnostic testing. Like other screens, NIPT can result in false positives and false negatives, and it is not considered diagnostic. Of the two tests, cfDNA, also referred to as noninvasive prenatal screening (NIPS) or noninvasive prenatal testing (NIPT), is more sensitive and specific. In addition, MSS assesses risk for ONTDs. Maternal serum screening (MSS) and cell-free DNA (cfDNA) screening estimate a patient’s risk of carrying a fetus with a chromosomal disorder. Most professional guidelines define prenatal genetic testing as encompassing two categories of testing: screening and diagnosis. Prenatal testing is offered to all pregnant women to identify pregnancies with a chromosomal disorder, such as trisomy 21 (Down syndrome), or an open neural tube defect (ONTD).
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