Preimplantation genetic diagnosis: State of the art

Preimplantation genetic diagnosis (PGD) is used to analyze embryos genetically before their transfer into the uterus. It was developed first in England in 1990, as part of progress in reproductive medicine, genetic and molecular biology. PGD offers couples at risk the chance to have an unaffected child, without facing termination of pregnancy. Embryos are obtained by in vitro fertilization with intracytoplasmic sperm injection (ICSI), and are biopsied mostly on day 3; blastocyst biopsy is mentioned as a possible alternative. The genetic analysis is performed on one or two blastomeres, by fluorescent in situ hybridization (FISH) for cytogenetic diagnosis, or polymerase chain reaction (PCR) for molecular diagnosis. Genetic analysis of the first or second polar body can be used to study maternal genetic contribution. Only unaffected embryos are transferred into the uterus. To improve the accuracy of the diagnosis, new technologies are emerging, with comparative genomic hybridization (CGH) and microarrays.