Individual assessment of sperm morphology of single spermatozoa used for intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) is an integral part of assisted reproduction. Although many papers have shown that global sperm count, sperm motility and sperm morphology of the ejaculate play no role in the fertilization rate after ICSI, embryologists who carry out ICSI, try to use the 'best looking' spermatozoa. The aim of the study was to investigate whether those spermatozoa with the best morphology really achieve the highest fertilization rate. In the present study, a total of 798 spermatozoa used for ICSI were documented by high-resolution photo. After ICSI the oocytes were cultured in single droplets and the formation of pronuclei was assessed 16 h later. The spermatozoa (all normal according to WHO criteria) were classified into four groups of different morphology. Group 1: normal head shape (approximately 5 microm diameter), group 2: like group 1, but with 15-20% smaller diameter, group 3: like group 1, but with 15-20% larger diameter, and group 4: like group 1, but with slight mid-piece cytoplasmic irregularities. Using the Pearson chi-square test, no significant difference in terms of fertilization was found among the different groups, showing that marginal sperm differences do not alter the fertilization process in ICSI.