Diagnosis of sex in preimplantation embryos by fluorescent in situ hybridisation.

The aim of prenatal genetic diagnosis is to give parents the option of terminating affected pregnancies. For most X linked conditions specific diagnosis is not possible and the only option is induced abortion of all male fetuses, of which half would be unaffected. An altemative is offered by preimplantation diagnosis of sex in embryos obtained by in vitro fertilisation and selective transfer of female embryos. The sex of preimplantation embryos has been determined by amplification of a DNA fragment specific to the Y chromosome by the polymerase chain reaction after biopsy of the embryo at the eight cell stage.' Live births of female infants have followed this procedure, testifying to its safety.2 Misdiagnosis is, however, possible because of contamination, failure of amplification, or the sampling of anuclear cytoplasmic fragments.' We report the application of dual colour fluorescent in situ hybridisation for sexing interphase nuclei of three day old human preimplantation embryos.