Study of nucleation status in the second cell cycle of human embryo and its impact on implantation rate.

OBJECTIVE: To study nucleation status in two- and four-cell embryos and its effect on reproductive outcomes.

DESIGN: Retrospective cohort study.

SETTING: University-affiliated private center.

PATIENT(S): A total of 1,679 embryos from 940 oocyte donation cycles from May 2012 to May 2014.

INTERVENTION(S): None.

MAIN OUTCOME MEASURE(S): Implantation, morphokinetics, and nucleation status restoration.

RESULT(S): Multinucleation was present in 42.53% of embryos with known implantation data at the two-cell stage; it was present in approximately 14% of them at the four-cell stage. In all, 73.4% of the embryos were multinucleated at two cells and restored their nucleation status when they cleaved into four cells. Embryos with blastomeres multinucleated (more than two nuclei) at the four-cell stage showed a lower implantation rate. The average length of S-phase in the first embryo cell cycle in the positive known implantation data (KID+) embryos was longer than in KID- (15.50 hours vs. 14.38 hours) and slightly shorter in the second embryo cell cycle (8.35 hours in KID+ vs. 8.60 hours in KID-).

CONCLUSION(S): Multinucleation in two-cell-stage embryos is a frequent event, which is reversible in a high proportion of embryos, without impact on the implantation rate; and embryos with multinucleated blastomeres have a reduced outcome compared with those with binucleated blastomeres when multinucleation is present in four-cell-stage embryos.