Received April 30, 1998
Accepted October 17, 1998

Introduction: One of the most important and unsolved problems in IVF is to decide which embryos are more suitable to implant and therefore should be transferred. Material and Methods: We analysed the in vitro development of isolated biopsied blastomeres and compared to the development of the original embryo, in order to find a relationship that could show embryos potential future development and increase implantation rates. Results: A total of 66 normally fertilized human embryos were biopsied at the 6- to 10- cell stage. At day 6, blastomeres were counted by nuclear labelling. A total of 33 embryos reached the blastocyst stage (50%). Of the isolated blastomeres, 63% divided and 53% cavitated over 3 days in culture. Of the blastomeres taken from embryos that developed to the blastocyst stage, 88% divided, 79% cavitated, 76% divided and cavitated and 9% neither divided nor cavitated; ln those from arrested embryos, 39% divided (p<0.001), 21% cavitated (p<0.001), 1 5% divided and cavitated (p<0.001) and 55% neither di vided nor ca vitated (p<0.001). Conclusions : Blastomeres biopsied from embryos that reached the blastocyst stage presented a significantly higher proportion of division and cavitation than those originated from arrested embryos. Culture of the isolated blastomeres can demonstrate the embryos with more likelihood to develop to blastocysts stage and that are probably more suitable to implant. Cryopreserving biopsed embryos and culturing blastomeres would increase implantation rates. Embryos can be selected according to the blastomere development and thawed for transfer in a future cycle.