Definition: Preimplantation genetic diagnosis is a procedure that allows a couple to have child that does not have specific conditions that are known to run in the family. In order to undergo preimplantation genetic diagnosis, a couple must have in vitro fertilization, which combines the egg and the sperm outside of the body to create an embryo. The embryo is then tested for a specific genetic condition. Any embryos that do not have the condition are then implanted in the woman’s uterus, and the pregnancy is allowed to continue.