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.