If Trisomy 18 sounds vaguely familiar, it may be because the condition has been in the public eye in recent years. Former Senator Rick Santorum’s daughter Bella has the condition and introduced America to Trisomy 18 during his presidential bid in 2012.
Most babies with T18 do not reach their first birthdays, although some children may survive longer, with severe disabilities.
A story about a Trisomy diagnosis
I saw a patient “Erica” recently for a follow-up ultrasound. She had been on my mind, and I was glad to see her looking cheerful and calm, very different from her state of mind when we first met. Two months ago, Erica was referred to me for consultation and ultrasound after a blood test in her OB’s office indicated that her fetus had an increased risk for Trisomy 18.
Fetuses with Trisomy 18 have an extra eighteenth chromosome in each of their cells.
Erica was nervous and upset at that first visit. Our genetic counselor explained to her that her serum screening test from her OB’s office showed a Trisomy 18 risk of 1 in 136. The test is reported as abnormal when the risk of a chromosome abnormality is greater than that of a 35-year-old patient. Erica was 21 years old, overwhelmed and shy, and clearly going to pieces with worry. Her husband was at work, and she had come to her appointment by herself.
The ultrasound didn’t help.
The fetus appeared normal for a 20-week pregnancy, with the exception of one small finding: choroid plexus cysts. Choroid plexus cysts are harmless fluid collections in the brain and are present in many normal fetuses, but they are a minor marker for Trisomy 18.
This means that they are seen more frequently in fetuses with Trisomy 18 than in normal fetuses.
The majority of fetuses with Trisomy 18 will have several ultrasound abnormalities, like poor growth, heart defects, hernias, or clenched fists. When choroid plexus cysts are the only abnormality, the risk of abnormal chromosomes doesn’t go up much. Unless you have another risk factor, like an abnormal serum screen.
What are the options?
We talked about her options at that point. Noninvasive blood testing for Trisomy 18, amniocentesis, or following her with ultrasounds and waiting until the birth of the baby to see if he had Trisomy 18.
She elected to have an amniocentesis. An amnio is a fairly straightforward office procedure; it only takes a minute or two, but there is a small risk of complications that may lead to miscarriage. And nothing is straightforward for a young woman who is terrified that her baby may have a life-limiting abnormality.
When the world just stops
When a test comes back abnormal, the world just stops.
Or more accurately, the world continues rushing forward, and YOU stop – frightened and isolated. Nothing that you hear makes sense. Your family, who loves you, will tell you that everything will be fine, fine. Your friends will tell you all about their pregnancy experiences, helpful or not.
And as for your visit with me, your doctor – serum screen, odds risks, choroid plexus cysts, amniocentesis, life-limiting condition – these phrases are meaningless when it’s your baby we’re talking about. Your mind leaps forward, “how will I deal with an abnormal baby?“. Then backward, “was it something I ate, drank, did?”
Erica had her amnio, and I sent her home with assurances that her baby was most likely normal and healthy. After all, the risk of Trisomy 18 was in the neighborhood of 1-2%. I asked her to try to stay positive. A few days later, when her result came back, I told myself that I had been mistaken to dangle hope – a shiny, cruel gift – before the amnio result was back.
I just wanted so much for her go home feeling better; she was so scared and miserable. But her baby had Trisomy 18.