[Medical aspects of diagnosis before implantation].

With the currently available techniques, it is not possible to perform cytogenetic and enzymatic analyses on 1 or 2 cells collected from a human embryo prior to its reimplantation. The recent techniques of polymerase chain reaction may allow DNA analyses in some cases: sexing or diagnosis of monogenic diseases. The reliability of these techniques and the absence of adverse effects due to embryo micromanipulation have to be demonstrated. The practical medical application of preimplantation diagnosis requires in vitro fertilization in a fertile couple and its low rate of success has to be compared to the reliability of the early prenatal diagnosis on chorionic villus samples.