Pronuclear zygote score following intracytoplasmic injection of hyaluronan-bound spermatozoa: a prospective randomized study

The aim of this study was to determine whether the early stages of embryo development, as assessed by the zygote score (Z-score), could be influenced by the injection of spermatozoa that had been preselected on the basis of their binding to hyaluronic acid (HA). A total of 407 sibling metaphase II oocytes, belonging to 44 different patients, were injected in a prospective randomized way, with either hyaluronic acid bound (HA+) or non-bound (HA−) spermatozoa. The fertilization rate (75-70%), the percentage of the different Z-scores (Z1: 22-24%, Z2: 22-22.5%, Z3: 44-45%, Z4: 12-8.5%), the mean score of the transferred embryos (3.76 ± 1.29, 3.78 ± 1.1) and the number of embryos at the 4-cell stage 45 h after injection (77-76%) were not different between the two groups. The ongoing pregnancy rate in this study (>20 weeks of gestation) was 36.4% per replacement, the implantation rate 28% and the twin pregnancy rate 44% (7/16). Although binding to HA did not apparently influence the Z-score, this agent continues to be used for the immobilization of spermatozoa prior to injection, on the basis that it is a natural product that can easily be metabolized by the oocyte via normal biological mechanisms.