10/24/2011 07:52 pm ET | Updated Dec 24, 2011

The Blood Test to Diagnose Down Syndrome Goes on Sale (Finally!)

Once again we are on the cusp of a maternal blood test for Down syndrome. Sequenom announced it would launch its test that diagnoses Down syndrome without an invasive test -- amniocentesis or chorionic villus samping (CVS). The familiar pundits weighed in: the doctor quoted in the New York Times lauding the benefit to women of fewer invasive tests; the anti-abortion advocate worrying about making it easier to terminate a Down-syndrome-affected pregnancy.

Here's my prediction: nothing will change for years. It will take a long time for this test (and the others like it that will launch in 2012) to impact obstetric medicine. There are a few reasons.

The Sequenom test, with the clever name MaterniT21, isn't perfect. In more than one percent of cases of Down syndrome, the test called the fetus normal. It also called a few normal fetuses abnormal. Few women are going to choose it over an amniocentesis or CVS because they select those tests for certainty, not "pretty sure." Most women who end up with an invasive test like amniocentesis or CVS already had a blood test that called them "high-risk" for Down syndrome, and then chose the invasive test (that carries a small risk of miscarriage) because the invasive test speaks certainty.

Then there is the cost: the new test costs $1,900 -- about as much as an amniocentesis or CVS. It seems unlikely to me that insurance companies are going to cover the test for two reasons. First, if the test comes back "Down syndrome," many women are going to want an invasive test to rule out the chance that the original test is wrong. This will double the cost of making the diagnosis.

But the real reason I suspect insurance companies won't cover this test is because it would open the door to using the test on everyone -- replacing the cheap, widely-available (but not-too-accurate) blood tests that estimates the risk of Down syndrome with a test that costs $1,900.

Naturally, Sequenom wants as many women to use its test as possible. The company suggested in its launch press release that 750,000 pregnant women at "high risk" for Down syndrome should use its test every year (that's nearly a quarter of the 4.3 million pregnancies annually in the U.S.).

Will anyone care that the Sequenom test was delayed a couple of years when the company's scientists fabricated their data? I doubt it. The company has clearly retained top-level consulting scientists in academia.

A good use for the Sequenom test at this point would be for the women (50,000 to 100,000) who are genuinely at high risk of carrying a Down-syndrome-affected fetus, either because they are over 40 years old (approximately 1-percent risk) or have a blood test result suggesting a 0.5- to 2-percent risk and can tolerate the uncertainty left in the Sequenom test in order to avoid an invasive procedure.

It will take my colleagues some time to sort this out (and to fend off the Sequenom sales reps who will accost us in the halls and at conferences). Meanwhile, I don't expect much to change when the test becomes available.