Down Syndrome | Causes & Risk Factors


Are some people more likely than others to have a baby who has Down syndrome?

If you have already had a baby who has Down syndrome, you are more likely to have another one. For every 100 couples who have another baby, 1 will have another who has Down syndrome. If you have been diagnosed with a chromosomal abnormality, you also have an increased risk of having a baby who has Down syndrome.

Additionally, the risk of Down syndrome increases with the age of the mother, as shown in this table:

Risk of Down Syndrome

Mother's age Chance of having a baby with Down syndrome
20 years 1 in 1,667
25 years 1 in 1,300
30 years 1 in 950
35 years 1 in 365
40 years 1 in 100
45 years 1 in 30


See a list of resources used in the development of this information.

Some of this content was developed by the University Centers for Excellence in Developmental Disabilities in CA (USC), MA (UMass Boston), IA (U of IA), KY (U of KY) and supported in part by the National Center on Birth Defects and Developmental Disabilities (NCBDDD) of the Center for Disease Control and Prevention through a cooperative agreement with Association of University Centers on Disabilities (AUCD). The opinions expressed are strictly those of the authors and do not necessarily reflect the opinions of the supporting organizations.

Written by editorial staff

Reviewed/Updated: 02/14
Created: 01/99