Genetic Testing for Down Syndrome

By ⁠Dr. Brandon Colby MD, an expert in genetic testing and personalized medicine.

Down syndrome is the most common chromosome-related disorder in the United States. Parents, especially older ones, worry about their baby suffering from it, as it can be quite debilitating. Fortunately, due to genetic testing for down syndrome, parents can learn about their baby’s risks.  

About Down Syndrome

Down syndrome, also known as trisomy 21, is a disorder that can lead to intellectual disabilities and health problems, such as hearing loss, thyroid problems, and heart defects. 

Down syndrome is a chromosomal disorder. Chromosomes are part of the cells in a body that contain genes. These genes are inherited from the mother and father. 

Usually, people have 46 chromosomes - two pairs of 23 chromosomes. One pair comes from the mother and the other comes from the father. 

Children who have Down syndrome have an extra chromosome - identified as chromosome 21. Unfortunately, this extra chromosome changes the way the body and brain develop. 

Chromosomal abnormalities can be identified during pregnancy with screening and diagnostic testing. 

Risk Factors for Down Syndrome

A mother’s age is one risk factor for Down syndrome. Many health care providers encourage pregnant women over 35 to screen for Down syndrome, as the risk increases with the women’s age. 

There is also an increased risk for mothers who already have a child with the condition.

Screening Tests for Down Syndrome

Prenatal tests can identify the risks a fetus will be born with the condition or diagnose it. The consideration many parents have to face though is that most screening tests carry a slight risk of miscarriage. 

Screening can be performed during the first trimester and second trimester. 

First Trimester Screening for Down Syndrome

During the first trimester starting around 10 weeks of pregnancy, a blood test and ultrasound can show signs of Down syndrome. The blood test can reveal levels of certain proteins in maternal blood. The ultrasound can show developmental issues that could indicate the fetus may have the disorder. 

Second Trimester Screening for Down Syndrome

If there was any sign of the disorder in the first trimester, a doctor may recommend a triple screen, which identifies three different substances. A quadruple screen may also be performed to look at four different substances. 

Depending on the results of the screenings, a doctor may encourage a diagnostic test to see if the fetus does indeed have the disorder. 

Understanding the Screening Results

Pregnant women who receive positive results during screening tests should seek guidance from a genetic counselor. A higher risk of having the genetic disorder doesn’t necessarily mean the baby will have it. Prenatal testing is reliable but they are not 100% accurate.

Diagnosis of Down Syndrome

These are three types of tests performed during pregnancy:

1. Amniocentesis: A small sample of amniotic fluid is extracted for analysis. 

2. Chorionic villus sampling (CVS): A sample of the placenta is removed for testing. 

3. Percutaneous umbilical blood sampling (PUBS): A blood sample is removed from the umbilical cord. This is the most accurate way to diagnose Down syndrome. 

A blood test can be performed on the baby after birth if pregnant women don’t want prenatal screening. Many women decide not to have diagnostic testing even if the screening tests show a high risk for the genetic condition due to the small risk of miscarriage. 

Why It’s Important to Know

Test results can prepare parents to care for their baby as soon as he/she is born. Early intervention can help decrease the severity of the symptoms. It can also help mitigate some of the medical conditions the baby may suffer from throughout development. 

Protect Your Baby with Genetic Testing

In addition to prenatal screening or genetic testing for Down syndrome, you can learn more about other risks with genetic testing.

Genetic testing can be performed at any time. Genetic testing before pregnancy, also known as carrier screening, can identify any possible threats if a couple decides to conceive. ⁠Genetic testing during pregnancy can identify any gene mutations the mother may be passing on to the fetus. Upon birth, genetic testing can be performed on a baby with a simple cheek swab. You can learn more about that in our article ⁠How Soon Can You DNA Test a Baby After Birth. 

⁠Genetic testing for babies is valuable because it can prepare parents to look for the signs of diseases and inherited conditions. For example, genetic testing for autism can warn parents of high risk for it, and as soon as symptoms present they can implement medications and therapies that will mitigate the symptoms to improve outcomes.

About The Author

Dr. Brandon Colby MD is a US physician specializing in the personalized prevention of disease through the use of genomic technologies. He’s an expert in genetic testing, genetic analysis, and precision medicine. Dr. Colby is also the Founder of Sequencing.com and the author of Outsmart Your Genes.

Dr. Colby holds an MD from the Mount Sinai School of Medicine, an MBA from Stanford University’s Graduate School of Business, and a degree in Genetics with Honors from the University of Michigan. He is an Affiliate Specialist of the American College of Medical Genetics and Genomics (⁠ACMG), an Associate of the American College of Preventive Medicine (⁠ACPM), and a member of the National Society of Genetic Counselors (⁠NSGC).