The strategy of group embryo culture based on pronuclear pattern on blastocyst development: a two center analysis.

PurposeTo compare two embryo grouping strategies.MethodsRetrospective time-course analysis in two different centres. Two culture protocols were used at the zygote stage: "Random Group" in which zygotes were randomly grouped and "Definite Group" in which zygotes were grouped based on pronuclear pattern. Embryo culture was extended to blastocyst stage. Primary and secondary outcomes were respectively the blastulation rate and the cumulative clinical pregnancy and implantation rates.Result(s)A similar blastulation rate [42 and 41% day (5 + 6) blastocysts] was obtained in the two groups. Conversely, after adjusting for baseline and cycle variables, cumulative pregnancy [adjusted Odds Ratio = 2.10 (95%CI: 1.08-4.07)] and implantation [adjusted Odds Ratio = 1.78 (95%CI: 1.06-2.97)] rates were significantly higher in the "Random Group" compared to the "Definite Group".Conclusion(s)Two strategies of group culture gave similar results in terms of blastulation rate but the random grouping of zygotes improves pregnancy and implantation rates in IVF-cycles.