Enhanced fertility after heat-induced hyperactivation

Objective: To determine sperm hyperactivation, kinematic parameters, and fertilizing capacity after pretreating sperm at 40°C for 4 hours. Design: Prospective study involving pooled donor sperm that were colloid washed and incubated at either 23°C (control) or 40°C (heat-treated) for 4 hours as pretreatment. After incubation, analyses were performed with a computer- assisted sperm analyzer, whereas separate portions of sperm were evaluated with the sperm penetration assay at 37°C. Setting: Clinical and academic research environment. Patient(s): Cryopreserved-thawed sperm from different donors (n = 5). Main Outcome Measure(s): Sperm kinematic and fertilizing parameters. Result(s): Heat pretreatment of sperm resulted in over 22 times higher hyperactive motility at hour 4 compared with the control. The other kinematic parameters were also different. The heat-pretreated sperm group had a significantly higher percent penetration of zona-free oocytes with more swollen sperm heads per oocyte and enhanced sperm binding. Conclusion(s): The results showed that hyperactivation was induced by pretreatment of sperm with 40°C heat, suggesting the involvement of heat factors in hyperactivation. The fertilizing capacity of sperm may be improved by the mild heat pretreatment when marked by the presence of heat-induced hyperactivation.