Terminating A Pregnancy Based On A Test

Beth Daley recently reported on prenatal screening errors:

Two recent industry-funded studies show that test results indicating a fetus is at high risk for a chromosomal condition can be a false alarm half of the time. And the rate of false alarms goes up the more rare the condition, such as Trisomy 13, which almost always causes death. Companies selling the most popular of these screens do not make it clear enough to patients and doctors that the results of their tests are not reliable enough to make a diagnosis. …

Now, evidence is building that some women are terminating pregnancies based on the screening tests alone. A recent study by another California-based testing company, Natera Inc., which offers a screen called Panorama, found that 6.2 percent of women who received test results showing their fetus at high risk for a chromosomal condition terminated pregnancies without getting a diagnostic test such as an amniocentesis.

Libby Copeland summarizes Daley’s findings:

The problem with the new class of prenatal screenings, which look at placental DNA in the mother’s bloodstream, is that these companies’ tests are not regulated by the FDA due to a loophole that dates back to the 1970s, Daley writes. So there’s no one evaluating their claims of accuracy. Many doctors appear not to understand how predictive the tests they’re giving are, since they often get information about a test’s purported accuracy from the salespeople selling them the tests.

Genetic counselors should be stepping in to explain the tests’ limitations to patients, Daley writes, but that’s not always happening. She points to an apparently smaller but growing group of women who gave birth to severely ill babies—some of whom died within days—after screens showed their fetuses at minimal risk. (In a separate story, she outlines one of these stories, and another about a healthy baby born after a prenatal screen predicted, supposedly with 97 percent accuracy, that he would be born with a fatal chromosomal disorder.)

The companies that make these tests say they’re studying the false positive rate, but they’re also poised to push back on the FDA’s looming efforts to regulate them. For now, the industry is policing itself, which doesn’t seem to be working out so well for a number of American women.

However, Emily Oster defends the tests as “a huge leap in accuracy over what was previously available”:

The problem may not lie in the claims made by the companies who make the tests, but in the interpretation of these results by doctors and patients. The earlier versions of the screening tests were so inaccurate that no one would think of acting on their results by terminating a pregnancy. The enhanced accuracy here may, perversely, encourage acting on this information when it is still not certain. But that problem can’t be fixed by the test manufacturers; it requires greater statistical literacy among doctors and patients.