RESUMEN
PURPOSE: To analyze the results of our transferred embryos, especially those that "changed" their blastomere nuclearity from Multinucleated (MN) to Mono-nucleated during development. METHODS: Pregnancies where at least one MN embryo was transferred were retrospectively evaluated and categorized in order to record and follow-up on the ones that were implanted. Embryos were classified as normal (when all blastomeres were mono-nucleated on day one and two of development), corrected (multinucleated embryos on day one that became mono-nucleated on day two) and non-corrected (multinucleated either on day one, on day two or both days). RESULTS: There were 633 transfer cycles analyzed. Thirty-three percent (206) had at least one embryo with a MN blastomere at a given stage of development. Pregnancy and implantation rates were 29.0% and 19.0% for the group of exclusively mono-nucleated embryo transfers, and 28.6% and 15.8% for the group with at least one MN embryo transferred. The pregnancy outcome for "corrected" and "non-corrected" embryos could be corroborated unequivocally in only 9 cases, with an outcome of 8 and 4 normal babies, respectively. CONCLUSIONS: Because the amount of data analyzed is not satisfactorily large, differences were not significantly different; however, a trend may exist showing that normal at term pregnancies obtained from corrected embryos are more likely to occur than those from non-corrected embryos. Nuclear observation on a daily basis should be one of the strategies used to select the best embryos for transferring, to improve implantation rates and avoid multiple pregnancies.