Birefringence properties of human immotile spermatozoa and ICSI outcome

In sperm samples with complete asthenozoospermia, pregnancies are achieved by intracytoplasmic sperm injection (ICSI), but this condition has a negative impact on fertilization and embryo development owing to the difficulty of identifying viable cells for oocyte injection. Is the selection of sperm cells with head birefringence properties under polarizing light a successful strategy to identify viable spermatozoa?

This study included 192 ICSI cycles with complete asthenozoospermia (83 ejaculated and 109 testicular samples) performed under polarized light. Two types of sperm head birefringence were distinguished: partial (presumably reacted spermatozoa) and total (presumably intact acrosome). In some sperm cells, no birefringence was present. The main outcome of the study was the cumulative live birth rate (cLBR) per ICSI cycle.

Seventy-three deliveries resulted with 38.0% cLBR per ICSI cycle. The injection of birefringent spermatozoa led to significantly higher rates of fertilization, embryo development and implantation compared with the absence of birefringence (P < 0.001). Similarly, the resulting cLBR were 53.6% and 9.0%, respectively (P < 0.001). Spermatozoa with partial head birefringence yielded significantly higher fertilization and embryo utilization rates compared with total birefringence. The cLBR showed the same trend (62.7% and 46.7%, respectively, P = 0.048). Multiple logistic regression analysis showed the pattern of partial birefringence to be strongly associated with live birth rate.

Immotile sperm cells with birefringence properties under polarized light have higher chances of inducing fertilization and embryo development compared with non-birefringent cells. In addition, a pattern of partial birefringence, associated with a reacted acrosome, is the strongest predictive factor for live birth delivery, both in ejaculated and testicular samples.