When do people get tested as a carrier for trisomy 18?

Translocation: If the edwards syndrome infant has translocation (joining of chromosomes) rather than a free-standing extra 18 chromosome (trisomy), then the parent may "carry" this translocation in balanced form without symptoms. Translocation carriers can have a 10-50% risk for future infants with edwards as opposed to the very small risk (<1%) when the child has trisomy 18.