PROLONGED SPERM-OOCYTE EXPOSURE AND HIGH SPERM CONCENTRATION AFFECT HUMAN EMBRYO VIABILITY AND PREGNANCY RATE

A reduced time interval of oocyte exposure to spermatozoa was investig ated to assess whether it could enhance oocyte development and improve embryo viability, especially in cases of male factor infertility. A t otal of 167 patients were included in a prospective randomized study. They were randomly allocated to two major study groups, A (n = 85) and B (control group; n = 82). The oocytes from group A patients were exp osed to spermatozoa for only 1 h; those from group B were exposed for 16 h. The two study groups were then subdivided according to semen qua lity for further analysis of the results. Significantly higher percent ages were obtained in group A than in group B in terms of the fertiliz ation rate (74 versus 68%, P < 0.025), cleavage rate (53 versus 41%, P < 0.005), pregnancy rate (27 versus 12%, P < 0.05) and implantation r ate (11 versus 6%, P < 0.05). In addition, an increased fertilization rate was achieved in oocytes exposed to male factor spermatozoa for on ly 1 h compared with the conventional incubation period (78 versus 65% , P < 0.01). Advanced cellular stages (55 versus 41%, P < 0.02) and hi gher implantation rates (13 versus 4%, P < 0.05) were attained in the subgroup whose oocytes were exposed to normal spermatozoa for Ih compa red with the male factor spermatozoa with the standard culture interva l. The higher fertilization rates, enhanced embryo development and via bility achieved in group A indicate that prolonged exposure of oocytes to high concentrations of spermatozoa is detrimental, decreasing sper m-oocyte interaction and subsequent embryo implantation, particularly in male factor patients.