Prediction of Human Sperm Fertilizing Ability by the Hyperactivated Motility Patterns

Abstract

Human sperm cannot fertilize oocytes immediately upon ejaculation, but must acquire the ability to bind and penetrate the zona pellucida. Hyperactivation, which is linked to the process of capacitation, is a vigorous pattern of sperm motility marked by wide-amplitude, high-velocity, whiplash movements of the flagellum. This study was performed to investigate the correlation between hyperactivated (HA) motility patterns assessed by computer-aided sperm analysis (CASA) and the fertilization rate (FR) in vitro. Swim-up sperm were collected in 135 IVF cycles with at least 3 oocytes collected. Because no cases satisfied the HA motility pattern of "Star-spin", patients were divided into 3 groups: Sperm with curvilinear velocity (VCL) ≥ 100 μM/sec, linearity (LIN) < 60% and amplitude of lateral head displacement (ALH) ≥ 5 μM were "All HA". Sperm with straight-line velocity (VSL) ≥ 40 μM/sec, LIN ≥ 60% and ALH < 5 μM were "Non-HA". Others were defined as "Transition phase". The FRs in 81 "All HA" cycles, 33 "Non-HA" cycles, and 21 "Transition phase" cycles were 79.5 ± 26.6%, 65.4 ± 32.5%, and 80.8 ± 27.3% respectively. There was a significant difference between "All HA" and "Non-HA" cycles in the FRs (P=0.018). In 27 (20.0%) of 135 IVF cycles, the FRs were ≤ 50% ("poor" group). Eleven (13.6%) of 81 "All HA" cycles, 12 (36.3%) of 33 "Non-HA" cycles, and 4 of 21 "Transition phase" cycles belonged to the "poor" group. There was a significant difference between "All HA" and "Non-HA" cycles (P=0.006) in these incidences. The better FRs were obtained in patients with "All HA" cycles, and lower FRs were obtained in those with "Non-HA" cycles. These findings suggest that the assessment of HA motility patterns by means of CASA could be one of the predictors of human sperm fertilizing ability.