Definition

Placenta-derived cell-free DNA (cfDNA) fragments in maternal blood are sequenced to screen for trisomy 21 (Down syndrome), trisomy 18 (Edwards), trisomy 13 (Patau) and sex chromosome aneuploidies. According to a meta-analysis, pooled sensitivity is 99.3% for Down syndrome, 97.4% for Edwards and 97.4% for Patau; specificity is 99.9% for all three. The test is a screening test, not a diagnostic one; a positive result requires invasive confirmation (amniocentesis/CVS), and sensitivity is lower in twin pregnancies.

Method

Next-Generation Sequencing

Accepted sample types

Special Tube

Description

24-chromosome NIPT and whole-genome CNV analysis of ≥7 Mb - IVD-CE.

Inheritance

The DNA analyzed is of fetal/placental origin and is distinct from the maternal genome; the aneuploidies tested are usually de novo (arising from a meiotic error) and are not inherited from a parent, but if a parent carries a translocation there may be a familial inherited component.

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Inheritance Patterns

Describes how a genetic condition is passed on within a family. There are five main patterns

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Carrier (Heterozygous / Homozygous)

Why it matters: In autosomal recessive inheritance, when each parent is a carrier (while both appear healthy), the chance of their child being born with the disease is 25% in each

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VUS (Variant of Uncertain Significance)

This is the situation where the test has detected a change in the DNA, but the role of this change in the development of disease is unconfirmed.

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How to Read a Genetic Test Result (Positive / Negative / VUS)

A genetic test result falls into three main categories

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Types of Genetic Tests

A genetic test is a type of medical test that detects changes in genes, chromosomes or proteins. Today there are more than 77,000 genetic tests available.

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