Some fixed/some vary
risks are specific to a couples family tree.
All pregnancies have ~ 4% risk of an unexpected outcome, from clefts to prematurity & others. The risk of a chromosome is lowest in the early 20's (~1/1700) & rises to 1/100 @ 40 & 1/50 >45. I encourage those with the question to seek out a geneticist @ a children's hospital or medical school for the a review of personal risk.