Reducing the time of sperm-oocyte interaction in human in-vitro fertilization improves the implantation rate

Abstract

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.

Short gamete co-incubation during in vitro fertilization decreases the fertilization rate and does not improve embryo quality: a prospective auto controlled study

“…This result supports the data of previous studies [3][4][5][12][13][14][15] but is called into question by others [10,11,22], which have shown an improvement of the morphological embryo quality and of the pregnancy and implantation rates. The difference methods used for gamete co-incubation could explain these conflicting results.…”

“…Based on this hypothesis, some investigators tried to test the beneficial effect of a shortened gamete contact on embryo quality and pregnancy rate. Some of them have shown an enhanced embryo quality and pregnancy rate after a brief gamete contact of 1 to 4 h [3,10,11], while others have described an equivalent embryo morphology or pregnancy rate compared to a 18 h incubation [12][13][14][15][16]. The fertilization rate in case of shortened gamete contact was usually unchanged except as reported by Lundqvist et al, which has described a decreased fertilization rate in the short insemination group compared to the standard one [14].…”

“…However, several studies of gamete kinetic interaction in vivo have shown that (1) gamete contact and fertilization occur within 20 min post coitus in mammals [1,2] and (2) an average number of 15 spermatozoa are observed, in vitro, in the cumulus after 15 min of gamete contact. Furthermore, 80% of oocytes are fertilized after 1-h exposure to spermatozoa [3][4][5]. On the other hand, reactive oxygen species (ROS) released by the cellular metabolism have been implicated in (1) fatty acid peroxydation causing a decrease in membrane fluidity [6,7], (2) DNA fragmentation [8] and (3) embryo developmental arrest [9].…”

Effects of cumulus cells removal after 6 h co-incubation of gametes on the outcomes of human IVF

“…A similar polyspermy rate was observed in routine short co-incubation when cumulus cells were left [6,19]. But the effects of early cumulus cells removal on polyspermy rate remained conflict.…”

“…Although oocytes were exposed to large quantity of sperm, only 10-20 sperm entered cumulus cells and further sperm did not enter later. Passage through cumulus cells in human oocytes was slow and appeared to require at least 2 h [19]. The sperm penetration in cumulus cells was gotten rid of when cumulus cells were removed at 2~4 h of insemination.…”