Determining the Risk of Birth Defects

How much information does one need to make a decision about life or death?


| Fall 2014



An infant's foot

Despite the black-and-white and either-or that we daydream is fundamental in modern medicine, in the end our choice is often just a best guess.

Photo by Flickr/Sabianmaggy

When my son Teddy settles into his numerous chins, he looks like a Chinese Winston Churchill. At the time of this writing, he is six months old, clocking in at a respectable 18 pounds 12 ounces and 26.75 inches long. Numbers comfortably above average. The numbers my husband and I don’t talk about any more are those that defined him before he was born.

When he was 12 weeks in utero, the number 3.8 triggered a cascade of genetic tests. That number was the measurement of what is called the nuchal translucency—the space in the tissue at the back of a baby’s neck. In the first trimester of pregnancy, having fluid accumulate in that space could mean a chromosomal abnormality. The average distance for nuchal translucency, my husband and I were told, is around two millimeters. For our baby, the doctor said, the high measurement suggested that the risk of Down syndrome or another chromosomal defect was about one in five. There was also a one in 10 chance of serious heart defects.

I felt the room spin. My husband tried to anchor us in the numbers. But one number leads you to other numbers and possibilities: gene deletions or additions, Noonan syndrome, cystic hygroma, diaphragmatic hernia, duodenal atresia. The best we could hope for was to rule most of them out, one by one, through testing and ultrasounds. If tests didn’t show anything definitive by 20 weeks, doctors said, the odds for something going wrong would drop back to something approximating normal risk.

Zero risk is impossible, of course, when it comes to making a human being. We accept that. But zero is the only direction to aim for. Every test result is another recalculation of risk; we hope the number gets smaller, and then smaller still. But as my husband and I moved through medical offices, and waded further into the realm of diseases our baby could have, our perception of safety became less quantifiable. Some tests were relatively new, or only partially informative—the test for Noonan syndrome can only identify 75 percent of the genetic markers for the disease. My logical husband became increasingly frustrated at the decrease in certainty. After five ultrasounds, an amniocentesis, an echocardiogram, two fetal anatomical surveys, and a microarray, he asked our doctor, “What’s the order of magnitude risk we’re talking about now? One in 10? One in 100?”

“We don’t know,” the doctor explained. Despite the black-and-white and either-or that we daydream is fundamental in modern medicine, in the end our choice is often just a best guess.

The tests stopped after 15 weeks, which left us 31 days to our destination of 20 weeks. Slowly it began to dawn on us that the results of all the tests wouldn’t say for sure if there was something wrong. And there were no more tests to do.