3 questions to ask about Down syndrome testing during pregnancy
September 10, 2019
In July, Olympic gold medal-winning gymnast Shawn Johnson East and her husband, NFL player Andrew East, shared a personal video about their pregnancy – and their doctor's concerns that their developing baby might have Down syndrome.
Around the eight-minute mark of the video, Shawn and Andrew discuss the moment their doctor discovered two concerning findings at their 20-week ultrasound: the baby's kidneys were dilated (a little more urine visible than normal), and the umbilical cord had just two blood vessels instead of three, which is also called having a single umbilical artery.
Neither condition is rare – 3% of normal fetuses have mild increases in fluid in their kidneys and about 1% of all fetuses have a single umbilical artery. However, having the two findings might be indicative of Down syndrome.
I was struck by her use of the word “helpless” to describe how they felt in that moment, adding to the stress they already were feeling having previously gone through a miscarriage. Shawn said that as "control freak" athletes and new parents, it was difficult to accept that there was nothing they could do to improve their baby's health. However, they could pursue genetic testing if they wanted to know for sure. They opted for testing, and the couple recently shared that their testing came back negative for genetic anomalies – their baby does not have Down syndrome.
As a maternal-fetal medicine specialist (MFM), I often see patients who have to make decisions like Shawn and Andrew did. Their story inspired me to share three basic questions to ask if your provider is concerned your baby might have Down syndrome.
1. Why do you think my baby is at risk for Down syndrome?
There are multiple reasons your doctor might be concerned about Down syndrome, the most common of which is the age of the mother. Research has shown that as women age, their eggs tend to develop more chromosomal anomalies.
Your doctor might also be concerned if you had an abnormal screening, such as:
- Cell free fetal DNA screen. Also known as non-invasive prenatal testing or screening (NIPT/NIPS), this screening examines DNA fragments in a pregnant woman's blood for potential indicators of a genetic condition. Many patients are choosing to have this test as part of routine prenatal care in the first trimester, even if they are at low risk for Down syndrome.
- First trimester nuchal translucency screen. This ultrasound exam measures the amount of fluid at the back of the baby's neck. Excessive fluid can indicate a risk for Down syndrome. Adding in results from blood work gives you a numerical risk for having a baby with Down syndrome.
- Second trimester multiple marker screen. This test measures risk factors associated with levels of specific substances in a pregnant woman's blood that come from the placenta, the baby, or both.
- Ultrasound. As in Shawn's case, certain physical findings seen on an ultrasound might be associated with Down syndrome.
2. Do you want to know for sure before delivery?
It comes down to your level of concern about the results. I've had plenty of patients who opt for Down syndrome screening and, when the results show elevated risk, decide not to pursue diagnostic testing. That decision is completely OK.
However, you might want to have more certainty whether your child has a genetic condition and potentially which one. Some patients choose to undergo genetic testing to get more information and feel more prepared, while others prefer not to know for their own personal reasons. It's entirely the parents' choice.
If you do want to know more, we can perform further testing. Talk to your provider, who can recommend the most appropriate test. Certain diagnostic tests are available only during certain trimesters and some carry a risk of pregnancy loss. Also, keep in mind that some tests require a longer waiting period to return results.
3. What options are available for my stage of pregnancy?
Below are the diagnostic testing options available during the first and second trimester if screening suggests an increased risk for Down syndrome. We do not screen for Down syndrome after the second trimester, but invasive testing can be performed in the third trimester if new ultrasound findings that are worrisome are found later in pregnancy.
In the first trimester, you can consider a diagnostic test such as chorionic villus sampling, which is a biopsy of placental tissue. We usually don’t recommend having another screening test after you've already had a positive one. However, I’m seeing more patients select cell free fetal DNA screening to avoid the risks of invasive testing.
If your pregnancy was considered low risk for Down syndrome but you had an abnormal NIPT, I’d recommend using this positive predictive value calculator from the National Society of Genetic Counselors to estimate the risk. Enter the condition for which your test came back positive (such as Down syndrome) and the age you’ll be at delivery. The calculator will give you the probability that the NIPT result was right and that your baby has Down syndrome. Young women are often surprised to learn that even though their test came back abnormal, the true risk of their baby having Down syndrome is less than 50%.
In the second trimester, you can consider amniocentesis (analyzing the fluid around the baby) or fetal blood sampling. These tests provide the most complete information but do carry a small risk (less than 1 in 300 for amniocentesis) of pregnancy loss. As such, many patients who have an abnormal second trimester screen opt for less-invasive NIPT over diagnostic testing.
Understanding your fetal ultrasound
Dr. Robyn Horsager-Boehrer explains step-by-step what obstetricians are looking for when they conduct 18- to 20-week ultrasounds on pregnant women. You'll see as they check for birth defects such as Down syndrome and spina bifida.
A word about abnormal ultrasound screenings
Counseling patients about abnormal ultrasound findings is more complex than discussing next steps after abnormal screening results. Recommendations in this scenario must be tailored to the specific abnormality the provider sees.
Some abnormalities, such as mild fluid collections in the kidneys and a small or absent nose bone are considered soft markers for Down syndrome, which means the trait is associated with but not necessarily indicative of the condition. Some of these markers are more indicative of a higher risk of Down syndrome, such as increased fluid buildup in the back of the neck.
If you have your full ultrasound report and want to learn more, consider entering the findings in this Down syndrome risk calculator from Perinatology. Here, you can use the cumulative findings to estimate the risk for the condition and help you decide whether to pursue genetic testing.
We typically don’t suggest another round of non-invasive testing when we see major anomalies unless we have a good idea of which genetic condition might be affecting the baby. Diagnostic testing for total number of chromosomes, as well as changes like small additions or deletions, will gives you more information in the setting of fetal abnormalities.
However, rapid advances in non-invasive testing are changing recommendations. If you're concerned, talk with an MFM about next steps that might include advanced diagnostic testing.
Like Shawn Johnson East, you might be nervous or worried about your pregnancy due to positive results from a Down syndrome screening. Whether you want to know more or you'd prefer not to pursue further testing, you can reach out to us for information, answers, and support at any point during your pregnancy.
To visit with an maternal-fetal medicine specialist, call 214-645-8300 or request an appointment online
