Effects of critical time-point for selection of early cleaving 2-cell embryos on the pregnancy outcomes of IVF

Abstract

OBJECTIVE: Evaluation of early cleaving time to 2-cell stage has been proposed for the selection of embryos with high implantation potential. In order to provide criteria for the selection of early cleaving 2-cell embryo, a prospective study was performed. DESIGN: A prospective clinical observation study. MATERIALS AND METHODS: Embryos that had cleaved early at 25 hours and 27 hours postinsemination were designated as EC (early cleavage)-1 and EC-2, respectively, while others were designated as NEC (non-early cleavage). Statistical analysis was performed using the unpaired student t-test and chi-square test. P<0.05 was considered statistically significancy. RESULTS: At least one early cleavage embryo was observed in 98 (51.5%) for the EC-1 and 44 (23.2%) for the EC-2 of the 190 cycles assessed. Clinical pregnancy rates were significantly higher in the EC-1 group (58.2%) compared to the EC-2 group (31.8%) or the NEC group (22.9%) (P<0.05). Clinical pregnancy rates and implantation rate were increased if at least one EC-1 embryo was produced, and the increased pregnancy outcome was related positively with the number of EC-1 embryo. When the number of EC-1 embryo transferred was 0 or 1, most pregnancies were singleton (88.0%, 87.5%, respectively). However, when the number of EC-1 embryo transferred was 2 or more, multiple pregnancy rates were increased up to around 40%. CONCLUSIONS: These results shows that 25 hours postinsemination is more effective than 27 hours as a critical time-point for the selection of early cleaving 2-cell embryos with high implantation potential, and that number of early cleaving embryos is an important parameter for the prediction of pregnancy outcome including the chance of multiple pregnancies.