Embryo biopsy Embryos of grade A, B or C with at least five blastomeres were biopsied (Joris et al., 2003) in the morning of day 3 after ICSI. These selection criteria to decide whether an embryo was suitable for biopsy were the same as those used to decide whether an embryo was transferable on day 3 in the regular ICSI programme without PGD. Before biopsy of one blastomere, the blastomeres were checked for the presence of nuclei. If consequently no nuclear material was found during fixation, a second blastomere was removed. Embryo biopsy was carried out in HEPES-buffered medium under oil using laser technology (Fertilase) as was earlier described in detail (Staessen et al., 2004).