The impact of the zona pellucida thickness variation of human embryos on pregnancy outcome in relation to suboptimal embryo development. A prospective randomized controlled study

BACKGROUND: The study represents a prospective randomized controlled study evaluating zona pellucida thickness variation (ZPTV) measurements versus conventional selection of embryos using classic embryo score criteria, prior to embryo transfer in human IVF/intracytoplasmatic sperm injection (ICSI). METHODS: Eighty-six patients having greater than or equal to3 embryos, with a classic embryo score of less than or equal to2.2, were allocated to either ZPTV measurement or classic embryo morphology score before embryo transfer. The technician selecting embryos using classic embryo scoring was not aware of the ZPTV measurement results. Of the embryos allocated to ZPTV measurements, only the embryos with the highest ZPTV were transferred. RESULTS: We found no differences in the pregnancy rate per embryo transfer between the two groups (34.4 versus 35.7 %). Neither did the implantation rates differ. However, significantly better results were obtained when ZPTV was used as the selection criteria in cases where all embryos had an asynchrony in development or a high embryo score (i.e. were of poorer quality) by classical evaluation (odds ratio = 2.51, confidence interval = 0.33-198). CONCLUSIONS: Using a normally-developed embryo with an optimal embryo score, no beneficial effect of using ZPTV measurement was seen. However, when only less optimal embryos were available to select for transfer, ZPTV provided a x 2.5 increase in the chance of achieving a clinical pregnancy.