Genetic Testing

“If you want CVS, you’ll have to decide within the next three days,” the genetic counselor told us.

My husband and I were sitting in the upscale office of the maternal fetal medicine (MFM) practice in downtown San Francisco. Our obstetrician had referred us here for genetic testing of our twins in addition to the ultrasound to check for thickness of the babies’ necks that can predict risk of some disorders.  I was still early in the pregnancy and although I was not yet close to 35, the “advanced maternal age” I had learned about as a medical student, a lot had changed since then. Now there were blood tests, which would help predict the odds of some genetic abnormalities in the fetus.

We met with the genetic counselor who explained that we had options.  We could get the blood tests just one time, or get them twice a few weeks apart with more precision, or for absolute certainty we could do amniocentesis once I was a few weeks more advanced. If we wanted to, we could do something called chorionic villus sampling (CVS) but that had to be done now. We were told that all the blood tests are validated for singleton pregnancies: with twins the uncertainty is even higher because we didn’t just have one baby about whose health we were trying to predict, we had two.  In fact for this very reason in other countries these blood tests are not routinely offered to parents of twins.

We are both doctors, but even so as first time parents we were confused by the options, and now, due to the urgency of deciding on CVS, we felt additional time pressure. Did we, after all, want CVS? “If you want to be sure,” he had said, “the genetic tests are the only way.” And that is true. But you can have the most perfect birth with the healthiest baby and die in a car accident on the way home from the hospital.

Even though we were far removed from our pediatric and OB rotations in medical school, we still remembered that the list of terrible things that can befall infants was far longer than the five or so diseases the counselor was proposing to test for and included obstetric complications at birth.  And, as we were quickly learning thanks to the San Francisco Parents of Multiples Club, there were all sorts of complications, which became more common with twins. Not just pregnancy complications, but complications arising from premature birth. Twins can be premature about half the time and when babies are very premature they can have severe lifelong complications, even if their genetics are impeccable.

Our world is uncertain and we are all constantly making decisions based on imperfect information. In medicine, we consider each possibility and assess the risk versus the benefit of the proposed intervention. For most medical interventions this assessment is more qualitative than quantitative. When it comes to genetic testing, however, the numbers are available, and because the decisions can hinge on personal preference and the discussion can be lengthy, it is relegated to a genetics counselor.

The thing is, while we make decisions in a variety of ways that can vary even within individuals based on decisions, in healthcare, often we decide based on trust. For some people, this type of decision can be clear. Nothing short of 100% certainty on these four genetic defects would be tolerated, and they know early on that they want an invasive procedure to get it, even if that wouldn’t be the case for most. I’ve also had physician friends who declined any type of screening reasoning that even if they found a genetic defect, they wouldn’t terminate the pregnancy, and therefore the test was not worth doing for psychological preparation alone.

There are some who research each proposed intervention to the hilt and make their own decision. But we are ill-equipped to evaluate the primary data. Even as scientists trained in reading research studies, we are only too aware of the biases that can lead to a “positive” study for an intervention, and too unaware of the context of the one study within the rest of the field.  In other words, even if we can read the study, if we are not experts in the field, it is difficult to discern how much to trust its results.

For the most part, we make these difficult decisions the way we make decisions about almost anything else. We consult the local expert. When it comes to our healthcare, the local expert is our doctor. We rely on our doctor to know the field and the relevant studies in context, to know what the published guidelines are, but more importantly, to understand what the evidence that these guidelines are based on is, and to be able to digest that for us in a reasonable recommendation for us that takes account our personal concerns.

We are unable to determine whether our doctor has the medical knowledge, but we can judge her the way we assess anyone else we encounter. Does she seem competent and does she seem to care? If the answer to both is “yes,” then we likely trust her.  And if we do, then she can explain the risks and benefits of any intervention, and walk us through the rationale for her recommendation, but in the end, we do as she recommends. If we don’t trust her, or we don’t trust her enough, then we will look for another local expert. That local expert may be our neighbor who encountered a similar problem, our friend who read a newspaper article on the topic and has a strong opinion, or the blog that pops up on Dr. Google.

In the end, even with all our advanced medical training, we decided to do what our doctor had recommended. She hadn’t sent us there for procedures. She had referred us for the blood tests, and that is what we did. Fortunately our twins were born at term without incident, which does not necessarily mean we made the right decision.

I’ve thought about this encounter often in the years since, especially when discussing various options with my patients. I try very hard to make sure that the patient not only hears, but absorbs what I tell them. I write down things for them to take home. Often, I find, people are glad to understand, but more than anything, they decide what to do much like my husband and I did: they make their decision based on whether they trust their doctor (me).

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