Limited importance of pre-embryo pronuclear morphology (zygote score) in assisted reproduction outcome in the absence of embryo cryopreservation

Objective To investigate the hypothesis that Z-score criteria represent a reliable predictor of implantation rate and pregnancy outcome in in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) cycles, excluding the possibility of embryo selection before the embryo transfer. Design Retrospective clinical study. Setting Centre of Reproductive Medicine, Department of Obstetrics and Gynecology, Arcispedale S. Maria Nuova (ASMN), Reggio Emilia, Italy. Patient(s) We analyzed 393 pregnancies obtained by IVF or ICSI cycles. Intervention(s) Morphologic evaluations of Z-score in pre-embryos obtained from IVF or ICSI cycles. Main Outcome Measure(s) Evaluations of Z-scores, implantation rate, and clinical pregnancy outcome. Result(s) We did not find any statistically significant correlation between the Z-score of 1032 embryos transferred in 393 embryo transfers and the implantation rate or the pregnancy outcome. In particular, the best Z-score identified (Z1, 7.2%) did not seem to correlate with embryo implantation rate or pregnancy outcomes any better than those with worse scores (Z2, 6.9% and Z3, 85.9%). Conclusion(s) Our results seem to confirm that Z-score alone cannot be considered a better tool than standard morphologic criteria for identifying, controlling, or selecting embryos with a better chance of successful ongoing pregnancy.