The End of Amniocentesis? (and the Discontents Thereof)

This blog has carried posts about the development of non-invasive prenatal testing for chromosomal or genetic abnormalities.  Because some DNA of a fetus (unborn baby) circulates in the mother’s bloodstream, it is now possible to identify genetic abnormalities just by drawing a blood sample from a pregnant woman’s vein.  The more traditional techniques, done much later in pregnancy, are amniocentesis and the related procedure chorionic villus sampling.  Those techniques are invasive, requiring obtaining a sample directly from a pregnant woman’s womb (with some risk to the fetus).  Because diagnosis of conditions such as Down syndrome may lead to the decision to have an abortion, pro-life advocates such as the late Dr. C. Everett Koop called amniocentesis “a search-and-destroy mission.”  One does not have to be too prescient to see the day, fairly soon, when the mission moves much earlier in pregnancy, is done non-invasively, and covers a host of not only serious disorders that greatly shorten the life of a born child, or abnormalities like Down syndrome, but other genetic diseases or even variations that may or may not be desirable.  It is also a short but timely step to consider how this will affect the number and timing of abortions in the future.

Geneticists remind us that we should be careful not to let concerns run ahead of the state of the art.  They point out, for example, that:

  • The current non-invasive tests are mainly focused on chromosomal abnormalities—specifically, three trisomies:  Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13).
  • By professional guideline and, in some states, law, non-invasive testing should only be done in pregnant women who are at high risk for bearing babies with one of these syndromes.
  • The tests are not fully diagnostic, but only screening tests.  A positive result should still be confirmed with one of the more invasive tests.
  • The tests may be highly sensitive and specific for what they are assessing, but that is not the same as having a high predictive value.  The predictive value of positive or negative results may not be well-established, and depends critically on how prevalent, or common, the condition being tested for is in the population being tested.  For example, a positive result of a very accurate test for a rare disease still has a low likelihood of having actually detected the disease in an individual who tests positive.  This is an entirely trustworthy, if seemingly counterintuitive, fact—trust me.
  • Consequently, at the present, non-invasive prenatal genetic testing should not be done routinely, and should be done only with prior and ongoing careful medical counseling.  Also, care should be taken that women not rush into a decision to terminate a pregnancy based on one of these tests, out of a sense of feeling pressured not to wait too late into pregnancy.  This last point is likely to be apropos as legislative restrictions on abortions after 20 weeks—which I generally consider laudatory—gain some traction.

It seems to me that the basic ethical issues are the same, but one’s day to day approach should keep the current state of the art in mind.   This post was prompted by my morning email from Medscape, with more detailed discussions here and here, a brief visionary statement here, and a brief very top-level comment on the implications for abortion, by Dr. Arthur Caplan, here.

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