Effect of shortened sperm-oocyte exposure time on human in vitro fertilization and embryo quality

Several human in vitro fertilization (IVF) studies have suggested that shortening the time of sperm-oocyte exposure from the conventional duration of 14 to 16 hours to 1 to 2 hours may improve outcome. However, the impact of implementing such a change in a given IVF program may vary according to the patient population and to the culture media and sperm insemination concentrations used and other laboratory-specific parameters. To assess the effect of such a change in our program, we conducted a prospective, randomized, blinded study involving 30 IVF cycles not considered to warrant intracytoplasmic sperm injection (ICSI) and in which at least eight oocytes were expected to be retrieved. Oocytes from each patient were randomly assigned in equal numbers to control (14 to 16 hours of exposure) and 2-hour exposure groups. All oocytes were inseminated 4 hours after retrieval and assessed for fertilization 14 to 16 hours later. Fertilization rates and embryo quality scores in the two groups were not significantly different. Overall fertilization rates for the control and 2-hour exposure groups were 67% and 63%, respectively, whereas embryo quality scores (± SEM) were 20.5 ± 0.9 and 22.4 ± 1.0, respectively. There were three cases in which there was failed fertilization in the 2-hour exposure group but not in the control group. In conclusion, at our center, shortening the time of sperm-oocyte exposure in cases not considered to warrant ICSI did not significantly improve fertilization or embryo quality. Any IVF program considering the reduction of its routine sperm-oocyte exposure time should consider performing a similar study before implementing such a change.