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Down Syndrome - What Increases Your Risk

Risk factors associated with Down syndrome vary according to its classification. Factors that increase the risk that a baby will have trisomy 21 type Down syndrome, the most common type, include:

Having an older mother. The risk of having a baby with a genetic problem increases as a woman gets older. Many doctors use 35 and older as the age at which the chance of having a child with this type of Down syndrome increases. This risk increases continually with advancing age.
Having a previous pregnancy in which the fetus had Down syndrome. Women who have had a pregnancy with trisomy 21 type Down syndrome have a 1-in-100 chance of having another child with the condition.²

Translocation-type Down syndrome is the only type that is sometimes directly inherited. But the majority of translocation-type Down syndrome cases are sporadic (random), with no known cause. Translocation accounts for about 4% of all cases of Down syndrome.¹

You may be a carrier of the translocation chromosome if you have:

A family history of Down syndrome. Translocation-type Down syndrome may have been passed on to you if other members of your family have the condition.
Had other children with this type of Down syndrome.

Mosaicism is a type of Down syndrome that produces extra genetic material in some of the baby's cells while the other cells develop normally. Mosaicism affects about 3 out of 100 people who have Down syndrome.⁴ The risk factors for mosaicism are similar to those for trisomy 21.

Questions still need to be answered about the specific risk factors for Down syndrome. So far, research has not found any environmental influences that contribute to developing the condition. Medical researchers do not know why chromosomes sometimes divide abnormally and make the extra genetic material that results in Down syndrome.

WebMD Medical Reference from Healthwise

Last Updated: February 10, 2010

This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.