Down Syndrome

Certain things increase the chance that you will have a baby with Down syndrome. These are called risk factors. Risk factors may be different based on the Reference type of Down syndrome.

Trisomy 21

Trisomy 21 is the most common type of Down syndrome. People with this type have an extra Reference chromosome Opens New Window (47 instead of 46) in every cell. Risk factors for this type include:

• Reference Being older when you get pregnant. The risk of having a baby with a genetic problem increases as a woman gets older. Many doctors believe that the risk increases for women age 35 and older. This risk keeps rising the older a woman gets.
• Having a previous pregnancy in which the fetus had Down syndrome. Women who have had a pregnancy with trisomy 21 Down syndrome have a 1-in-100 chance of having another child with the condition.^{Reference 2}

Mosaicism

This type of Down syndrome is caused by only some cells producing 47 chromosomes. Mosaicism affects up to 3 out of 100 people who have Down syndrome.^{Reference 3} Risk factors for mosaicism are similar to those for trisomy 21.

Translocation

Translocation type is the only type of Down syndrome that may be passed through families, but most of the time it happens randomly. A person with this type has 46 chromosomes, but part of one chromosome breaks and then attaches to a different chromosome. Up to 4 out of 100 people with Down syndrome have the translocation type.^{Reference 4}

You may be a Reference carrier Opens New Window of the translocation chromosome if you have:

• A family history of Down syndrome.
• Had other children with this type of Down syndrome.

If you are thinking about becoming pregnant and you're at risk for having a child with Down syndrome, you may want to see a Reference geneticist Opens New Window or Reference genetic counselor Opens New Window. They can help you understand your risk and work with you on genetic testing.

© 1995-2011, Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Reference Terms of Use. Reference How this information was developed to help you make better health decisions.