Down Syndrome Risk Factors

Researchers have found that it is more likely for an older mother to have reproductive cells with an extra copy of chromosome 21. So an older mother is more likely to have a baby with Down Syndrome than a younger mother.

However, most of the babies who have Down Syndrome (about 75%) are born to mothers who are 35 or younger. This is because older mothers tend to have fewer babies. (Only about nine percent of total births occur in mothers over age 35 – but about 25% of babies with Down Syndrome are born to women in this age group.)

The likelihood that a woman under age 30 who becomes pregnant will have a baby with Down syndrome is less than one in 1,000, but the chance of having a baby with Down Syndrome increases to 1 in 400 for women who become pregnant at age 35. The likelihood of Down Syndrome continues to increase as a woman ages, so that by age 42, the chance is one in 60 that a pregnant woman will have a baby with Down syndrome, and by age 49, the chance is one in 12.

Because the chances of having a baby with Down Syndrome increase with the age of the mother, many health care providers recommend that women over age 35 have pre-birth testing for the condition. Testing the baby before it is born to see if he or she is likely to have Down Syndrome allows parents and families to prepare for the baby’s special needs. 

Parents who have already have a baby with Down Syndrome or who have abnormalities in their own chromosome 21 are also at higher risk for having a baby with Down Syndrome. 

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National Down Syndrome Society