Experts warn prenatal screening tests may lead to false positive results in some cases

Non-invasive prenatal testing (NPNI) on pregnant women to detect the risk of a fetus having rare genetic abnormalities can often be wrong, according to recent reports. These tests, according to several health experts, can actually give false positives, which can create significant anxiety in future parents.

Health experts told Fox News that NIPT works by taking blood samples from the pregnant mother and then analyzing fragments of the cells’ free DNA (cfDNA). The screening test then predicts the risk of a baby being born with certain genetic abnormalities. Some patients opt for these screening tests over diagnostic tests such as amniocentesis because they are less invasive to the fetus, health experts told Fox News.

Genetics specialists and obstetricians told Fox that non-invasive prenatal testing worked well to screen for fetal risks for common chromosomal disorders like Down syndrome, but said the tests are not as accurate for conditions relatively rare associated with chromosomal microdeletions such as Wolf-Hirschhorn syndrome.

File photo of a pregnant woman. Non-invasive prenatal tests may not be as accurate as other tests in diagnosing certain conditions.


Dr Siobhan Dolan, vice president of systems for research in the Department of Obstetrics, Gynecology and Reproductive Sciences at Icahn School of Medicine at Mount Sinai in New York City, told Fox News he is important for expectant parents to recognize that these types of maternal blood tests are screening tests and not real diagnostic testing.

“Screening tests assess risk, but they are NOT diagnostic. All screening tests have associated false positive and false negative rates – they are never 100% accurate,” Dr Dolan told Fox.

Dolan, who is also director of the Genetics and Genomics Division at Mount Sinai, added: “It is really difficult to screen for very rare diseases, even if you have a great screening test. The results of screening tests must therefore be fully interpreted. differently from diagnostic test results – and that’s where the confusion comes in. “

Dolan explained to Fox News that diagnostic tests are done during pregnancy by chorionic villus sampling or amniocentesis, which takes DNA from the fetus, which allows genetic testing.

“It provides accurate information and will determine whether a fetus has a genetic disease or not,” Dolan said. “But there is a small risk of miscarriage due to the procedure (1/500 – 1/1000), so some women don’t want to have these procedures,” Dolan added.


According to health experts, tests such as NIPT are used to detect chromosomal disorders caused by the presence of an extra or missing copy (aneuploidy) of a chromosome. Primarily, non-invasive prenatal testing detects the risk to the fetus of common chromosomal conditions, including trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). The tests have now expanded to be used to detect other rare chromosomal diseases and conditions associated with chromosomal microdeletion disorders, according to multiple reports. Depending on the disorder, the accuracy of the test may vary, according to experts.

Researchers in a 2017 report published in the Journal of Obstetrics and Gynecology said tests involving screenings for “microdeletions did not demonstrate a false positive rate low enough to be considered practical or ethically acceptable.” The authors of this study also stated in the published report that “false positive rates can be as high as 90% for some diagnostic tests for microdeletions” and suggested that diagnostic tests seem preferable for maximizing the detection of microdeletion syndromes or of microduplication which can lead to mental disorders and physical development problems in a baby.

Nurse drawing blood from a pregnant woman.

Nurse drawing blood from a pregnant woman.


The American College of Obstetricians and Gynecologists (ACOG) revised its position on non-invasive prenatal testing (NIPT) in 2020. ACOG has approved both serum protein screening and cfDNA NIPT in all pregnancies for women. chromosomal abnormalities common to all pregnant patients, regardless of age or otherwise. risk factors. (Previously, screening was only recommended for people 35 years of age and older or those with other known risk factors). However, Dolan told Fox that ACOG advises against the routine use of these screening tests for microdeletion syndromes.

ACOG said in its 2020 guidelines: “Screening of a limited number of microdeletions with cell-free DNA is available; however, this test has not been clinically validated and is not recommended ”.

The ACOG also noted in its guidelines that drug tests are not equivalent to diagnostic tests and warned doctors to be aware of potential false positives as well as false negatives.

A pregnant woman receives medical advice.  Prenatal screening may not provide the diagnostic accuracy desired by expectant parents.

A pregnant woman receives medical advice. Prenatal screening may not provide the diagnostic accuracy desired by expectant parents.


Dolan told Fox News that genetic counselors play an important role in educating patients about the risks, benefits and limitations of genetic tests they may want to undertake during pregnancy. Dolan said his colleagues at the Mount Sinai Health System educate patients BEFORE choosing their testing route to make sure they understand the difference between screening tests and diagnostic tests.

“It is important to know BEFORE your screening test results come back that an increased risk result means a diagnostic test is recommended – it does not mean the fetus is affected.”
For some people who want to be sure, Dolan recommended that they ignore the uncertainty of drug tests and go straight to diagnostic tests.

“It’s a good choice for many pregnant people,” Dolan told Fox News.

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