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 to spermatozoa in vitro. A total of 119 patients were assigned to two study groups in a randomized prospective study in which each patient's oocytes were exposed to spermatozoa for either 1 h (group 1 - 58 patients) or the standard 16 h incubation period (group 2 - 61 patients). The fertilization rate obtained in group 1 was higher than in group 2 (285/393, 73%, and 272/410, 66% respectively), suggesting that the spermatozoa-oocyte interaction occurs within 1 h. This was confirmed in a study in vitro using fluorescently labelled spermatozoa and normal oocyte-cumulus complexes. Spermatozoa enter the cumulus complex within 15 min, traverse the cumulus layer within 3 h, and first appear in the oocyte 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 characteristics of embryos from both study groups. However, when evaluating 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. The implantation and pregnancy rates for group 1 were 11 and 28%, while the corresponding rates for group 2 were 8 and 15%. This suggests that a reduced exposure of oocyte to spermatozoa favours embryo viability, possibly due to a decrease in potential damage from sperm metabolic waste products.
Gianaroli
L
L
S.I.S.M.E.R., Medicine Reproductive Unit, V. Mazzini, 12, 40137 Bologna, Italy.
Cristina Magli
M
M
Ferraretti
A P
AP
Fiorentino
A
A
Tosti
E
E
Panzella
S
S
Dale
B
B
D000328:Adult; D010064:Embryo Implantation; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D006801:Humans; D007246:Infertility / Q000628:therapy; D008297:Male; D011446:Prospective Studies; D013084:Sperm-Ovum Interactions; D013997:Time Factors