Down Syndrome Risk Factors

Advanced maternal age is the only known risk factor for Down syndrome. The older the woman is when she delivers the infant, the higher the chances of having a child with Down syndrome.

• At age 25: the risk is 1 in 1,250
  
  
• At age 30: the risk is 1 in 1000
  
  
• At age 35: the risk is 1 in 400
  
  
• At age 40: risk is 1 in 100
  
  
• At age 45: the risk is 1 in 30

Couples who have had one child with Down syndrome are at a slightly increased risk (about 1%) for having another affected child. The risk of having a baby with Down syndrome is increased, if one of the parents has a translocation involving chromosome 21. The recurrence risk is as high as 100% if the carrier parent has a translocation in which two chromosomes 21 are fused.

People with Down syndrome rarely reproduce. About 15% to 30% of women with trisomy 21 are fertile, and they have a 50% risk of having an affected child. Men with Down syndrome are even less fertile, but at least one case is known, in which a man with Down syndrome fathered a child.