How can Trisomy 21 be prevented? What Prenatal Testing can be done?

Although there is no way to prevent Down syndrome, there is less than a 1% chance (depending on the age of the mother) that parents who have a child (or other relative) with Down syndrome will have another baby with the same genetic abnormality. When there is an increased risk because of a mother's age (35 years or older) or a history of genetic defects in a family, parents may want to use screening and diagnostic tests.