Prenatal genetic test results need to be communicated better, according to the US Food and Drug Administration (FDA).
The FDA published a report highlighting to patients and healthcare professionals that non-invasive prenatal testing (NIPT) can only convey the risk of a fetus having a genetic condition, and are not diagnostic in most situations. Only invasive tests – amniocentesis or chorionic villus sampling (CVS) – can give a definitive diagnosis.
'Without proper understanding of how these tests should be used, people may make inappropriate health care decisions regarding their pregnancy,' said Dr Jeff Shuren, director of the FDA's Centre for Devices and Radiological Health. 'We strongly urge patients to discuss the benefits and risks of these tests with a genetic counsellor or other health care provider prior to making decisions based on the results of these tests.'
NIPT isolates and analyses small amounts of DNA that cross from the placenta into the pregnant woman's bloodstream. The advantage over traditional prenatal genetic tests is that it can rule out some types of abnormalities without the associated one percent risk of miscarriage inherent in amniocentesis and CVS. However, NIPT alone cannot definitively confirm the presence of most fetal genetic abnormalities.
The FDA highlighted that NIPT is over 99 percent accurate at ruling out certain genetic conditions, such as Down's syndrome. However, some US companies are offering NIPT for very rare mutations where small amounts of the chromosome are missing, called microdeletions, and for these applications the accuracy level can be lower and may lead to false-positive results.
Following the FDA warning, The New York Times reported on the false positive rate of NIPT for microdeletions, showing that 80-93 percent of positive results could be errors. The article quoted women who received false-positive screening results for extremely rare conditions, and highlighted examples of misleading marketing by companies selling the tests.
Currently, one in three pregnant women in the USA currently choose to have NIPT, and one test maker, Natera, reported that they had performed more than 400,000 microdeletion screenings.
In the UK NIPT is being rolled out across the NHS for the trisomies that cause Edward's, Patau's and Down's syndromes only. It is part of a pathway where risk of these conditions is first assessed by ultrasound and blood tests. People whose pregnancies are identified as higher risk are offered a non-invasive test, and if this also indicates high risk, a diagnostic amniocentesis or CVS test is offered to give a definitive answer.
Sources and References
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F.D.A. warns patients about some prenatal genetic tests
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FDA warns of risks associated with non-invasive prenatal screening tests
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Genetic non-invasive prenatal screening tests may have false results: FDA safety communication
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FDA warns against relying on genetic screening tests to make prenatal diagnoses
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The FDA warns prenatal screening tests may give false results: What this means if you're pregnant
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When they warn of rare disorders, these prenatal tests are usually wrong
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