Preimplantation diagnosis of aneuploidy using fluorescent in-situ hybridization: evaluation using a chromosome 18-specific probe.

Fluorescent detection of in-situ hybridization (FISH) with a chromosome 18-specific probe (P5041 B.5 D18Z1) has been used to assess the use of this method for preimplantation diagnosis of aneuploidy. Interphase nuclei (n = 802) have been analysed from 59 normally fertilized embryos developing in vitro at the normal rate between days 2 and 7 postinsemination. The efficiency of hybridization in control cells, as assessed by the proportion with two signals in normal female lymphocytes was 88.9% (n = 353) and with three signals in a trisomic (48,XXX+18) fibroblast cell line 74.0% (n = 290). Fifty-four of the human embryos were considered to be diploid on the basis that the majority of nuclei had two signals. Some nuclei in these embryos had one or no signal, especially on day 2, and tetraploid nuclei were also widespread. Among the remaining five embryos, one 5-cell embryo on day 2 had three hybridization signals in 4/5 nuclei and was trisomic for chromosome 18, one 4-cell embryo on day 2 had only one signal in 4/4 nuclei and was monosomic, and the three other embryos were aneuploid mosaics and/or had multi-nucleated blastomeres. Analysis of the incidence of interphase nuclei with more or less than the diploid number of hybridization signals indicates that more than a single nucleus will be necessary for accurate preimplantation diagnosis of aneuploidy.