What is the Risk for Down Syndrome?

Some parents have a greater risk of having a baby with Down syndrome. The risk factors include:

Maternal Age

As a woman’s eggs age, there is a higher risk of the chromosomes dividing incorrectly. Therefore the risk of Down syndrome increases with a woman’s age.

Previous child with Down syndrome

Generally, couples who have had one child with Down syndrome have a slightly increased risk (about 1%) of having a second child with Down syndrome.

A carrier parent

Parents who are carriers of the genetic translocation for Down syndrome have an increased risk depending on the type of translocation, therefore prenatal screening and genetic counseling are important.

People with Down syndrome rarely reproduce. Fifteen to thirty percent of women with trisomy 21 are fertile and they have about a 50% risk of having a child with Down syndrome. There is no evidence of a man with Down syndrome fathering a child.

While the incidence of births of children with Down syndrome increases with maternal age, more children are born to women under the age of 35 due to higher fertility rates. Eighty percent of children with Down syndrome are born to women under the age of 35 years.

What is the difference between a Screening Test and a Diagnostic Test?

A screening test will help identify the possibility of Down syndrome. Screening tests do not provide conclusive answers, but rather, they provide an indication of the likelihood of the baby having Down syndrome. An abnormal test result does not mean that your baby has Down syndrome. The goal with a screening test is to estimate the risk of the baby having Down syndrome. If the screening test is positive and a risk for Down syndrome exists, further testing may be recommended. Diagnostic tests can identify Down syndrome before the baby is born.

In the January issue of Obstetrics & Gynecology, the American College of Obstetricians and Gynecologists released guidelines recommending screening for Down syndrome to all pregnant women during their first trimester.

Diagnostic tests tend to be more expensive and have a degree of risk; screening tests are quick and easy to do. However, screening tests have a greater chance of being wrong; there are “false-positive” (test indicates the baby has the condition when the baby really does not) and “false-negatives” (baby has the condition but the test indicates they do not).