REDUCING THE TIME OF SPERM-OOCYTE INTERACTION IN HUMAN IN-VITRO FERTILIZATION IMPROVES THE IMPLANTATION RATE

Human oocyte development was evaluated after a reduced time exposure t o spermatozoa in vitro, A total of 119 patients were assigned to two s tudy groups in a randomized prospective study in which each patient's oocytes were exposed to spermatozoa for either 1 h (group 1 - 58 patie nts) or the standard 16 h incubation period (group 2 - 61 patients). T he fertilization rate obtained in group 1 was higher than in group 2 ( 285/393, 73%, and 272/410, 66% respectively), suggesting that the sper matozoa-oocyte interaction occurs within 1 h. This was confirmed in a study in vitro using fluorescently labelled spermatozoa and normal ooc yte-cumulus complexes, Spermatozoa enter the cumulus complex within 15 min, traverse the cumulus layer within 3 h, and first appear in the o ocyte cortex at 4 h post-insemination, The incidence of polyspermy was higher in oocytes exposed to spermatozoa for 16 h (3%) than for 1 h ( 1%). There was no difference in the cleavage rate or morphological cha racteristics of embryos from both study groups, However, when evaluati ng the timing of embryo development, group 1 generated a significantly higher percentage of four to five cell embryos when compared to group 2 (55 versus 39%; P < 0.001), documented at 40 h post-insemination, T he implantation and pregnancy rates for group 1 were 11 and 28%, while the corresponding rates for group 2 were 8 and 15%, This suggests tha t a reduced exposure of oocyte to spermatozoa favours embryo viability , possibly due to a decrease in potential damage from sperm metabolic waste products.