Is it necessary to focus on morphologically normal acrosome of sperm during intracytoplasmic sperm injection?

The detailed assessment of sperm morphology is important in the semen of infertile men because there is a low proportion of normal spermatozoa. One of the parameters of such sperm morphology is the acrosome, and its effect on assisted reproductive outcomes is controversial. This study was undertaken to evaluate the association between different forms of acrosome on the chromatin status and the assisted reproductive outcomes.

A total of 1587 unstained sperms from 514 infertile men were captured and analyzed for different acrosome forms (normal, large, small, skew, amorphous acrosome and without acrosome) in real time during intracytoplasmic sperm injection into oocytes. The association between the percentage of sperms with atypical acrosome and head shapes and the sperm chromatin status was studied. Fertilization, zygote and embryo quality and clinical pregnancy rates were calculated for different groups of sperms.

The highest frequency of irregular shapes of acrosomes, such as small, large and amorphous, was observed in abnormal ellipticity, anteroposterior symmetry and angularity parameters, respectively (P <0.05). The fertilization rate of injected sperms with large (P <0.01) and small (P=0.001) acrosomes and without acrosome (P=0.001) was significantly lower in comparison with normal acrosomes. The quality of zygotes (Z3, P=0.05), embryos (grade C, P <0.05) and the pregnancy rate (P=0.001) from injected sperms with large acrosomes were significantly lower compared with normal acrosomes.

Our findings showed that the different sperm acrosome morphologies (e.g., large, small, and without acrosome) might negatively relate with chromatin integrity and decrease the sperm's fertility potential and pregnancy rate during intracytoplasmic sperm injection (ICSI) cycles.