The U.S. government plans to regulate a booming prenatal testing market that has recently come under scrutiny for a high share of false positive results for some rare conditions and marketing that could mislead parents.

In a notice posted this month, the Food and Drug Administration said it intended to write rules to “make explicit” that it had the authority to oversee laboratory-developed tests, a category of screening and diagnostic tests developed and used within a single lab.

The new regulations would cover noninvasive prenatal tests, which use a small blood sample to screen for genetic abnormalities in a fetus during the first trimester of pregnancy. In just over a decade, these tests have gone from relatively obscure laboratory experiments to an industry that serves more than a third of the pregnant women in America.

The screenings are very accurate when they look for more common genetic disorders like Down syndrome. But newer tests that claim to detect rare abnormalities usually get their positive results wrong, a New York Times investigation found last year.

The Times’s investigation found that, when these tests screened for rare diseases, their positive results were wrong 80 percent to 93 percent of the time. But on product brochures and test result sheets, companies often described the tests to pregnant women and their doctors with the language of near certainty. They advertised their findings as “highly accurate,” offering “total confidence” and “peace of mind.”

Those results can cause significant distress for parents, requiring follow-up testing that can be invasive and expensive. Some genetic counselors described cases to The Times in which expectant parents had decided to terminate a pregnancy based on a screening they later learned was a false positive.

“The F.D.A. is very concerned about problematic LDTs currently used in the U.S. that might not provide patients with accurate and reliable results,” said James McKinney, an F.D.A. spokesman, about laboratory-developed tests.

The agency’s concerns about laboratory-developed tests extend beyond prenatal screenings. It has described problems with tests for heart disease and autism that could lead to improper treatments. This month it announced a pilot program for laboratory-developed tests used in cancer drug trials. It will ask some drugmakers to voluntarily report accuracy data on their tests that it could then make public.

In April last year, the F.D.A. issued a specific warning about the risks of false positives from noninvasive prenatal tests, instructing doctors not to make suggestions based on these results alone and stressing the need to follow positive screenings with more reliable diagnostic testing. It said it was “aware of reports” that some women “ended pregnancies based only on the results” of these screening tests.

“While genetic noninvasive prenatal screening tests are widely used today, these tests have not been reviewed by the F.D.A. and may be making claims about their performance and use that are not based on sound science,” Dr. Jeff Shuren, the director of the agency’s center for devices and radiological health, said in a statement at the time.

Experts who reviewed the testing companies’ marketing materials for The Times said they were “problematic” and made claims based on numbers that were “meaningless.”

F.D.A. regulation could mean marketing for tests like these would need to be submitted to the government for approval. The agency could say tests it deems “high risk,” like those that would inform major medical decisions, would have to go through a federal review process before reaching the market.

The F.D.A. considered regulating these tests a decade ago before backing away. Legislators have repeatedly introduced bills that would give the F.D.A. authority to oversee laboratory-developed tests, but none have passed.

A draft of the F.D.A.’s new proposed rule is expected to be published this summer and figures to face significant pushback. The regulation may draw legal challenges from test manufacturers, who have previously argued the agency does not have the authority to regulate this type of product.

“There will clearly be some challenges because the laboratories are really opposed to this,” said Alberto Gutierrez, the former director of the F.D.A. office that oversees many medical tests. He said he thought the F.D.A. had jurisdiction, “but working through the legal challenges will probably take a while.”

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