Screening for Down syndrome

Thanks to Becky Wilcox, site supporter, for this post.

One out of every 691 babies born each year will have Down syndrome making it the most common chromosomal abnormality. First named by English physician John Langdon Down, the condition occurs when a person has a full or partial extra copy of their 21st chromosome. Simply put, they have 22 pairs of all chromosomes plus one set that has three.

The decision to screen for Down syndrome is a personal choice between you, your partner and doctor. Some parents-to-be feel strongly about having these answers as soon as possible so they can pursue additional confirmatory testing and guide future healthcare decisions. Others choose not to know at all.

What are the risk factors for delivering a baby with Down syndrome?

Down syndrome occurs in all races and ethnicities with no clear link to its cause, but there are some risk factors that we know raise the chances of your baby being born with the disorder. These include:

• Maternal age of 35 or older (though babies with Down syndrome can be born to younger mothers)
• Previous birth of a baby with Down syndrome
• Being a carrier of the genetic translocation for Down syndrome

How will I be tested for Down syndrome?

Most doctors offer screening tests for Down syndrome in the first or second trimester.  Some tests must be completed earlier than others, but they should all be done no later than your 20th week. It’s best to complete them as early as possible.

Your doctor may use a combination of blood work and ultrasound technology to gather more information about your baby’s risk for Down syndrome and other chromosomal abnormalities. In the past, samples would be taken from the amniotic sac and results were returned as a percentage or risk ratio that had to be interpreted by your doctor. Newer screening tests called cell-free DNA tests look at fetal DNA existing in your own bloodstream and does not have to compromise your baby’s sterile environment.  Referred to as “noninvasive” options, these tests can indicate a likelihood that abnormalities may be affecting the pregnancy.  You will need additional testing based on the results of your blood work and ultrasounds to confirm a diagnosis.  This may include invasive tests like chorionic villus sampling (CVS) or amniocentesis.

Can noninvasive prenatal testing tell me about other genetic conditions?

Yes.  Some noninvasive prenatal tests will screen for a spectrum of genetic conditions—not just Down syndrome. Some conditions that can be detected include:

• Trisomy 18 (Edwards syndrome)
• Trisomy 13 (Patau syndrome)
• Rarer chromosomal abnormalities like DiGeorge syndrome, Jacobsen syndrome, Cri-du-chat syndrome and others

What is the outlook for a child with Down syndrome?

Children with Down syndrome may also have other health problems at birth. About half are born with some type of heart condition that could be life threatening, and may require corrective surgery. In addition, people with Down syndrome have a higher risk for other health problems including:

• Leukemia
• Infectious diseases
• Dementia
• Obesity
• Vision problems
• Sleep apnea

Children born with Down syndrome are living longer, better lives than they did a century ago and many are integrating into today’s schools, community organizations and workforces.  Most people with Down syndrome will possess some form of cognitive delay ranging from mild to severe that will shape how they live and how much care or supervision is required from day to day.

Only you can decide

No screening tool for Down syndrome is guaranteed to be 100% accurate and the decision to have prenatal genetic testing is unique to you and your situation. Talk with your doctor to learn more about the risks and benefits associated with testing, consider your risk factors and move forward with the decision that feels right for you.