Preimplantation genetic diagnosis

Preimplantation embryo biopsy is now technically feasible for
some genetic disorders and available in a few specialised
centres. In this method in vitro fertilisation and embryo culture
is followed by biopsy of one or two outer embryonal cells at the
6–10 cell stage of development. DNA analysis of a single cell or
chromosomal analysis by in situ hybridisation is performed so
that only embryos free of a particular genetic defect are
reimplanted. An average IVF cycle may produce 10–15 eggs,
of which five or six develop to the stage where biopsy is
possible. The reported rate of pregnancy is about 20% per
cycle and confirmatory genetic testing by chorionic villus
biopsy or amniocentesis is recommended for established
pregnancies. This method may be more acceptable to some
couples than other forms of prenatal diagnosis, but has a very
limited availability.