The predictive value of using a combined Z-score and day 3 embryo morphology score in the assessment of embryo survival on day 5

Background: The purpose of this study was to evaluate the ability of using the Z-score alone, or, in combination with the day 3 embryo morphology score, to predict embryo viability at day 5 from a large cohort of embryos derived from patients undergoing treatment with IVF/ICSI. Methods and results: In this retrospective study, a total of 1894 zygotes from 346 treatment cycles (295 couples) was analysed between January 2001 and May 2002. The Z-scoring system was useful in predicting day 5 embryo survival. The mean ± SD day 5 embryo survival rates were 78.2 ± 1.7, 49.0 ± 2.5, 21.4 ± 3.2 and 11.8 ± 5.6% for Z-1, Z-2, Z-3 and Z-4 zygotes groups respectively. Embryos derived from Z-1 scores and grade I day 3 embryo scores showed the best day 5 embryo survival and a very high implantation potential. Conclusions: These data suggest that a combined evaluation of the Z-score and day 3 embryo morphology is highly predictive of embryo outcome after IVF/ICSI. The Z-score could be of great help in the selection of embryos for cultures extended to later stages. The Z-score alone, or preferably in combination with day 3 embryo morphology, is useful in the determination of the most suitable embryos and the number of embryos for transfer, thus achieving the optimal chance of conception while reducing the risk of high order multiple pregnancy.