OBJECTIVE: To determine the prognostic impact of the embryo nuclear status at day 2 among other major morphologic parameters (first cleavage at day 1, number of blastomeres and anuclear fragmentation at day 2) on the birth rate.
DESIGN: Retrospective study.
SETTING: Hospital IVF department.
PATIENT(S): Women undergoing 1,629 day 2 transfers of 2,732 embryos from May 2006 to November 2008.
INTERVENTION(S): Four groups according to the embryo nuclear status.
MAIN OUTCOME MEASURE(S): Implantation, miscarriage, and birth rates.
RESULT(S): Univariate analysis indicated significantly higher birth rates when all blastomeres were mononucleated (15.0%) compared with embryos with not all blastomeres mononucleated (9.2%), embryos without any visible nucleus (7.7%), and embryos where at least one blastomere was multinucleated (4.2%). Multivariate analysis found significant decreased birth rates when multinucleated blastomeres were observed.
CONCLUSION(S): Blastomere nuclear status should be added to the kinetic and morphologic criteria traditionally used at day 2 to assess human embryo quality. The presence of multinucleated blastomeres has a negative impact on birth potential. The results argue for integrating the blastomere nuclear status at day 2 with the kinetic and morphologic criteria traditionally used to define the best embryo to transfer. Embryos with a single visible nucleus in all blastomeres should be given priority for transfer when available.