People of any race, sex, or socioeconomic background can have Down syndrome, but certain parents have a higher chance of having a baby with the condition. The main factor that increases risk is the age of the pregnant person, especially age 35 and older.
Main risk factors
- Advanced maternal age: The chance of having a baby with Down syndrome rises steadily with age; for example, estimates go from roughly 1 in 1,000–1,400 in the mid‑20s to around 1 in 100 by age 40. Even so, most babies with Down syndrome are born to younger women, because younger people have more pregnancies overall.
- Previous affected pregnancy or parental chromosome change: Parents who already have a child with Down syndrome, or who carry a specific chromosome rearrangement (a translocation involving chromosome 21), have a higher chance of having another baby with Down syndrome.
Who is not specifically at higher risk
Down syndrome occurs in all ethnic groups and income levels, and typical lifestyle or environmental exposures are not known to cause it. Most parents of children with Down syndrome have normal chromosomes themselves and no clear risk factors other than age.
