The impact of the source of spermatozoa used for ICSI on pronuclear morphology

BACKGROUND: The aim of this prospective study was to find out whether the source of spermatozoa used for intracytoplasmic sperm injection (ICSI) has an impact on the morphological features of pronucleate zygotes, which make up the basis of a pronuclear scoring system for the selection of the most viable embryos for transfer. METHODS AND RESULTS: The study group consisted of 194 two pronucleate (2PN) ICSI zygotes, of which 144 originated from ejaculated (ES) and 50 from testicular spermatozoa (TS). At 18 h postinjection, 2PN zygotes were assessed for pronuclear alignment, polarity in nucleoli and cytoplasmic appearance; all of which were found to exhibit similar patterns of distribution between the ES and TS groups (P = not significant). At 25 h, the presence of first cleavage was similar for both groups; 11 % of zygotes in the ES and 10 % of those in the TS group underwent early cleavage (P = not significant). At 48 h, a quality score was obtained for cleaving embryos by multiplying the number of blastomeres with the grade of the embryo. Pronuclear scoring in both groups of spermatozoa correlated with embryo quality score at 48 h postinjection. There was a trend for a higher incidence of early cleavage and a lower incidence of pronuclear arrest with better pronuclear scoring embryos for both types of spermatozoa. CONCLUSION: The morphological features of pronucleate zygotes at 18 h after microinjection with ES and TS are similar to each other.