The problem of erroneous prenatal testing

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02 Jan 2022, 12:55 pm

When They Warn of Rare Disorders, These Prenatal Tests Are Usually Wrong
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In just over a decade, the tests have gone from laboratory experiments to an industry that serves more than a third of the pregnant women in America, luring major companies like Labcorp and Quest Diagnostics into the business, alongside many start-ups.

The tests initially looked for Down syndrome and worked very well. But as manufacturers tried to outsell each other, they began offering additional screenings for increasingly rare conditions.

The grave predictions made by those newer tests are usually wrong, an examination by The New York Times has found.

Nonetheless, on product brochures and test result sheets, companies describe the tests to pregnant women and their doctors as near certain. They advertise their findings as “reliable” and “highly accurate,” offering “total confidence” and “peace of mind” for patients who want to know as much as possible.

Some of the companies offer tests without publishing any data on how well they perform, or point to numbers for their best screenings while leaving out weaker ones. Others base their claims on studies in which only one or two pregnancies actually had the condition in question.

These aren’t the first Silicon Valley firms to try to build a business around blood tests. Years before the first prenatal testing company opened, another start-up, Theranos, made claims that it could run more than a thousand tests on a tiny blood sample, before it collapsed amid allegations of fraud.

In contrast with Theranos, the science behind these companies’ ability to test blood for common disorders is not in question. Experts say it has revolutionized Down syndrome screening, significantly reducing the need for riskier tests.

However, the same technology — known as noninvasive prenatal testing, or NIPT — performs much worse when it looks for less common conditions. Most are caused by small missing pieces of chromosomes called microdeletions. Others stem from missing or extra copies of entire chromosomes. They can have a wide range of symptoms, including intellectual disability, heart defects, a shortened life span or a high infant mortality rate.

Some of the companies offer tests without publishing any data on how well they perform, or point to numbers for their best screenings while leaving out weaker ones. Others base their claims on studies in which only one or two pregnancies actually had the condition in question.

These aren’t the first Silicon Valley firms to try to build a business around blood tests. Years before the first prenatal testing company opened, another start-up, Theranos, made claims that it could run more than a thousand tests on a tiny blood sample, before it collapsed amid allegations of fraud.

In contrast with Theranos, the science behind these companies’ ability to test blood for common disorders is not in question. Experts say it has revolutionized Down syndrome screening, significantly reducing the need for riskier tests.

However, the same technology — known as noninvasive prenatal testing, or NIPT — performs much worse when it looks for less common conditions. Most are caused by small missing pieces of chromosomes called microdeletions. Others stem from missing or extra copies of entire chromosomes. They can have a wide range of symptoms, including intellectual disability, heart defects, a shortened life span or a high infant mortality rate.

But it is clear some of the tests are in widespread use. One large test maker, Natera, said that in 2020 it performed more than 400,000 screenings for one microdeletion — the equivalent of testing roughly 10 percent of pregnant women in America.

To evaluate the newer tests, The Times interviewed researchers and then combined data from multiple studies to produce the best estimates available of how well the five most common microdeletion tests perform.

The analysis showed that positive results on those tests are incorrect about 85 percent of the time.

Experts say there is no single threshold for how often a test needs to get positive results right to be worth offering. They note that when the tests do accurately identify an abnormality, it can give expectant parents time to learn about and prepare for challenges to come.

But there are hundreds of microdeletion syndromes, and the most expansive tests look for between five and seven, meaning women shouldn’t take a negative result as proof their baby doesn’t have a genetic disorder.

There are few restrictions on what test makers can offer. The Food and Drug Administration often requires evaluations of how frequently other consequential medical tests are right and whether shortfalls are clearly explained to patients and doctors. But the F.D.A. does not regulate this type of test.

Patients who receive a positive result are supposed to pursue follow-up testing, which often requires a drawing of amniotic fluid or a sample of placental tissue. Those tests can cost thousands of dollars, come with a small risk of miscarriage and can’t be performed until later in pregnancy — in some states, past the point where abortions are legal.

The companies have known for years that the follow-up testing doesn’t always happen.

After being presented with some of The Times’s reporting, half a dozen of the largest prenatal testing companies declined interview requests. They issued written statements that said patients should always review results with a doctor, and cautioned that the tests are meant not to diagnose a condition but rather to identify high-risk patients in need of additional testing.


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