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

Abstract 

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 45h after injection (77–76%) were not different between the two groups. The ongoing pregnancy rate in this study (>20weeks 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.

Keywords: hyaluronic acid, ICSI, nucleogenesis, Z-score, pronucleus