What are the risks associated with genetic testing? It's not all about the numbers
For several years as a prenatal genetic counselor, I spent my days discussing pregnancy risks with expecting women and couples. One of the most common reaons for referral was a screen-positive result on maternal serum screening. (At the time, first-trimester screening was in its infancy, so I'm referring here to second trimester screening) This blood test is performed in the second trimester of pregnancy and outputs the risk for spina bifida, Down syndrome, and trisomy 18 based on three (or, now, four) maternal serum proteins.
It's intention is to flag those pregnancies that are at higher risk, so that further investigation with high-resolution ultrasound and/or amniocentesis can be offered. It's real effect is to scare the living daylights out or pregnant women, who often assume that their baby definitely has the condition instead of simply an increased risk for the condition.
Here is a common risk-communication scenario:
The results of the maternal serum screen indicate a 1 in 100 chance for the fetus to have Down syndrome. That's 1%. Or, turned around, there is a 99/100 chance or 99% chance that the fetus does NOT have Down syndrome.
However, to find out for certain, amniocentesis must be performed. There is a chance of pregnancy loss with amniocentesis that's usually quoted around 1 in 200, or 0.5%.
The risk of pregnancy loss is lower than the risk of Down syndrome. If you were making a decision based solely on the numbers, it makes sense to have the amniocentesis performed.
However, it should not surprise you that people making decisions about their pregnancy and future child aren't concerned only with the numbers. They are concerned about lots of other factors: facing the possibility of a child with disabilities, making a choice about abortion, miscarrying a healthy pregnancy, getting poked with a big needle. I think you get the picture.
Often, it boils down to what I like to call the "rock or a hard place" question. Would you feel worse if you delivered a child with Down syndrome and didn't have the diagnosis prenatally, or if you found out you experienced pregnancy loss because of amniocentesis?
Nobody wants to make that kind of decision, and nobody does it based just on the numbers. Throw in the complexity nature of families, reproduction, marital relationships, past experience with disability, and so many other factors, and you can understand why it's call genetic counseling.
Nicole Teed, MS, CGC
We never know when when our turn might come
Our daughter is expecting her second child and had the second ultrasound while I was visiting last week. Everything looked good and they even learned--unintentionally--the baby's gender. The next day, a call came from the office requesting that she schedule a repeat ultrasound.
As Alex says in his comment, no reason was given. When I left town to return home, she was balancing her common sense--the ultrasound was done too rapidly and simply missed some measurements needed to complete the chart, but there is no suspicion of a problem--with her fears--there's something wrong.
Haven't heard the results yet, but her fears and mine will remain. Sometimes I really wonder whether we were better off when we didn't have all the diagnostic tools we have now. Knowledge--even accurate knowledge--can be a fearsome thing.
Marie
Avoiding Numbers
Nicole -
My wife and I went through this very thing a few years ago with our first child.
Just as you described it, we had the blood test and it came back positive. This was right around the Christmas holidays, so a nurse called us on our cell phone while we were out of town to schedule an appointment with a genetic counselor. She wouldn't give us the test results nor any details over the phone, but said it was "serious" and we needed to come in "as soon as possible." We knew immediately that the test had come back positive.
Numbers, probabilities, increased risks...none of those meant anything to us for the next week or so. All we could think about over the holiday was how we felt about having a child with Down syndrome.
Could we live with that? Did we have enough time to schedule an amniocentesis, find out those results, and then get an abortion, if we decided to go that route?
Our meeting with the genetic counselor didn't help things. Not that it was her fault; she just wasn't in a position to alter our course. I do remember thinking our counselor was a bit like a statistician and psycologist rolled into one person. She explained how to intrepret the results of the test, as well as explored with us how we felt about our various options. It was emotionally draining and we left more determined to see this thing through to the bitter end and have an amnio.
Of course, everything turned out fine. Our daughter is now three years old and she just became a big sister with the arrival of our second child. This time, however, we chose not to take this test nor have an amnio. We came to realize the minimal value of knowing the numbers. And I have to say it was a huge relief to us to simply not factor them in on this second go-around.
Alex