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New Testing for Down Syndrome: The Establishment Pushes Back

My hunch is that obstetricians on the front lines -- the ones who counsel pregnant women every day about their testing options -- will realize that the new tests are just plain better. Patients of all ages -- who can inform themselves more easily than ever before -- will demand them too.
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When the new, non-invasive prenatal test for Down syndrome was introduced at South Shore Hospital last year where I practice, patients were offered several options:

  1. They could have an invasive test -- an amniocentesis or a chorionic villus sampling -- that is 100 percent accurate but occasionally causes miscarriage.

  • They could choose the new, highly-accurate, non-invasive prenatal test (we offered the Harmony test from Ariosa Diagnostics).
  • They could choose the older screening test for Down syndrome that requires one or two blood draws and an ultrasound. This test is quite sensitive (the test is "positive" 95 percent of the time when the fetus has Down syndrome), but is designed to tell 5 percent of all women that their fetus is at increased risk for Down syndrome even though it almost certainly isn't.
  • Patients were annoyed. They understood the pros and cons of the invasive test (certainty vs. a small risk of miscarriage). But they couldn't understand why we were offering them an older test that isn't as good as the newer test.

    We stopped offering the older test.

    We thought we were doing our patients a service. But to listen to the "Wise Women (and men) of Obstetrics," we were being rash, or as the latest article on this topic put it, practicing "beyond the boundaries of available evidence." So why the disconnect between what patients say they want and what the senior experts advise?

    In spite of scientists' best efforts, the available tests to screen for Down syndrome and other common chromosomal abnormalities simply weren't very good -- until recently.

    No one wants a long needle stuck into their uterus, even if the test results are perfectly accurate. More importantly, the rare miscarriage that results from an amniocentesis or chorionic villus samping test is unquestionably heartbreaking.

    The older screening test was enormously problematic: First, results took the form of a "risk." Hundreds of my patients over the years have looked at me with a blank face when I said: "Your screening result says you have a 1 in 700 risk of having a baby affected by Down syndrome." They had no idea what I meant. I would try to explain it lots of different ways, but frequently, I knew I had failed to communicate the meaning of that risk. Besides the complexity, the best version of the test failed to warn women that their fetus was affected with Down syndrome at least 5 percent of the time. More problematic was the 5 percent screen positive rate, which meant that literally one in 20 women got a "positive" result even though their fetus was almost certainly normal. The sheer terror that those results caused represented an enormous failure on the part of the obstetric community.

    Then along came non-invasive prenatal testing in late 2011, and within a year, four companies offered a version of this blood test, including the Harmony test from Ariosa Diagnostics that we use at South Shore Hospital in Massachusetts, 15 miles South of Boston. These tests all take advantage of genetic sequencing technology and fast computers to measure tiny differences in the amount of extra (or missing) genetic material from the fetus circulating in a woman's blood. The published results were nothing short of astounding: near-perfect risk assessment of Down syndrome, and 80-97 percent detection of other aneuploidies, with a false-positive rate significantly below 1 percent.

    What was the response from the "Wise Women (and men) of Obstetrics?" Was it jubilation? Was it gratitude toward the scientists who had brought forth testing worthy of our patients? No -- it was caution.

    The "Big Three" societies of prenatal diagnosis -- the American College of Obstetricians and Gynecologists, the Society for Maternal-Fetal Medicine, and the International Society for Prenatal Diagnosis -- all took the official position that the new test should be kept from low-risk women (generally those under 35 years old) because the test hadn't been proven in that population.

    This strikes me as a little bit like saying that a test for sickle cell disease shouldn't be used by caucasian patients because the test was developed in a black population (where sickle cell disease is more common). That's one of the nice things about biochemistry: It's colorblind.

    Medicine's most prestigious journal took up this torch last week by publishing an article that used a complex explanation of statistical principles to make the same point. I have nothing against complex statistics (which would be antithetical to my training as a physician) but rather I am puzzled by the disconnect between the widespread reluctance among the nation's obstetric cognoscenti (bet you want to be part of that club) to embrace this new technology and the overwhelmingly positive experience of patients who are using it.

    My hunch is that obstetricians on the front lines -- the ones who counsel pregnant women every day about their testing options -- will realize that the new tests are just plain better. Patients of all ages -- who can inform themselves more easily than ever before -- will demand them too.

    For more by Adam Wolfberg, M.D., click here.

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