My wife is pregnant. Wanting to be a supportive spouse, I attended the first prenatal visit to see one member of her team of midwives. (Being a "minimalist" I was, like my wife, fond of the idea of not unnecessarily "medicalizing" the [usually] natural act of labor and birth.) I realized during that first visit that understanding the intricacies of medical decision making can be a double-edged sword when dealing with practitioners, especially outside of one's specialty. If ignorance is bliss, 'tis folly to be wise, it is said. I've come to wonder which is better for you when you get entangled in US healthcare, wisdom or bliss.
During the first visit, we were offered, with an air of agnosticism, a referral for genetic counseling +/- non-invasive prenatal testing (NIPT). "How accurate is it," I naturally inquired, trying to avoid technical terms such as sensitivity and specificity. "Something like 99%" came the reply. So we were given the referral. But I quickly realized that this was a classic problem of base rates. The likelihood of a chromosomal abnormality is so low given my wife's age, that even extremely high sensitivities and specificities are inadequate to guide our decision - that is, the test is rendered practically useless because of the low base rates in our case. And this despite the fact that the sensitivities and specificities of
prenatal blood testing are inflated by the way they were derived. But think of the decision we would have faced had we blindly proceeded with testing without this consideration - given the low base rate, the posterior probability of a chromosomal abnormality such as Down's Syndrome given a "positive" test result would be around 33%. How would we act on this information? Is that threshold high enough that we would consider an elective abortion (if we were morally disposed towards that as an option)? Or would we ignore the information and proceed to term? And if we were not ethically accepting of elective abortion as a possibility, what other remedy would we have that would justify the information from the testing? Why would we talk about getting prenatal genetic testing before talking about the choices we may have to face after we receive the results? Why would not a discussion of remedies, specifically abortion, precede consideration of the testing? How many couples dive into the rabbit hole only to wonder how they got there and how they can get out? In this case, we decided that ignorance was indeed bliss, and deferred NIPT.
At that same visit, blood was ordered to be drawn. I had difficulty understanding why you would need to draw blood from a perfectly healthy woman at 12 weeks gestation. Blood types and anemia and all that I guessed. But I was particularly caught by the thyroid testing. Why are we screening an asymptomatic woman for thyroid disease? Is that justified by the prior probabilities? It takes only a google search to learn that ACOG (the American College of Obstetrics and Gynecology) and an endocrine society do not recommend universal testing. But my questioning why we were doing this was off-putting and frankly unanswerable for the midwife - she was just following the usual routine, whatever her supervisors and mentors had told her to do, without understanding....well without understanding any of this Bayesian mumbo jumbo that I was hinting at. Alas, thyroid testing, like NIPT, was deferred. But not for long.
