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 s ource of spermatozoa used for intracytoplasmic sperm injection (ICSI) has a n impact on the morphological features of pronucleate zygotes, which make u p the basis of a pronuclear scoring system for the selection of the most vi able embryos for transfer. METHODS AND RESULTS: The study group consisted o f 194 two pronucleate (2PN) ICSI zygotes, of which 144 originated from ejac ulated (ES) and 50 from testicular spermatozoa (TS). At 18 h postinjection, 2PN zygotes were assessed for pronuclear alignment, polarity in nucleoli a nd cytoplasmic appearance; all of which were found to exhibit similar patte rns 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 z ygotes 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 embr yo. Pronuclear scoring in both groups of spermatozoa correlated with embryo quality score at 48 h postinjection. There was a trend for a higher incide nce of early cleavage and a lower incidence of pronuclear arrest with bette r 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.