Embryo quality and impact of specific embryo characteristics on ongoing implantation in unselected embryos derived from modified natural cycle in vitro fertilization

Objective: To study the implantation potential of unselected embryos derived from modified natural cycle IVF according to their morphological characteristics. Design: Cohort study. Setting: Academic department of reproductive medicine. Patient(S): A series of 449 single embryo transfers derived from modified natural cycle IVF. Intervention(s): None. Main Outcome Measure(s): Ongoing implantation rate according to embryo characteristics. Result(s): The best implantation was found in embryos with 4 and 8 cells on day 2 and 3 respectively, <= 10% fragmentation, and absence of multinucleated blastomeres. In contrast to findings from other studies, we found embryos with fewer than four blastomeres on day 2 to do relatively well. Furthermore, we found the implantation potential of embryos containing multinucleated blastomeres to be less severely impaired than expected. Conclusion(s): Findings from this study suggest that in currently used embryo scoring systems, the implantation potential of embryos with low numbers of blastomeres on day 2, as well as embryos containing multinucleated blastomeres, is underestimated. However, it is unclear whether the results of our study apply to embryos derived from controlled ovarian hyperstimulation cycles. (Fertil Steril(R) 2010;94:527-34. (C) 2010 by American Society for Reproductive Medicine.)