Fertilization and early embryology: Prolonged sperm-oocyte exposure and high sperm concentration affect human embryo viability and pregnancy rate

Abstract

A reduced time interval of oocyte exposure to spermatozoa was investigated to assess whether it could enhance oocyte development and improve embryo viability, especially in cases of male factor infertility. A total 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 exposed 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 quality for further analysis of the results. Significantly higher percentages were obtained in group A than in group B in terms of the fertilization 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 rate (11 versus 6%, P < 0.05). In addition, an increased fertilization rate was achieved in oocytes exposed to male factor spermatozoa for only 1 h compared with the conventional incubation period (78 versus 65%, P < 0.01). Advanced cellular stages (55 versus 41%, P < 0.02) and higher implantation rates (13 versus 4%, P < 0.05) were attained in the subgroup whose oocytes were exposed to normal spermatozoa for 1 h compared with the male factor spermatozoa with the standard culture interval. The higher fertilization rates, enhanced embryo development and viability achieved in group A indicate that prolonged exposure of oocytes to high concentrations of spermatozoa is detrimental, decreasing sperm-oocyte interaction and subsequent embryo implantation, particularly in male factor patients.

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.…”

“…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

“…This generally corresponded to the time for pronuclei observation. However, some studies suggested that an extensive time of oocyte exposure to sperm affected embryo viability and pregnancy rate [4,5]. Compared with conventional IVF, shorter exposure of oocytes to sperm had favourable effects on embryo quality and pregnancy rate due to reduce the negative effects producing by high concentration of sperm and the corresponding metabolic products [5,6].…”

“…Short co-incubation of gametes reduces the time of oocyte exposure to sperm from 16 to 20 h to 1~6 h, even to 30 s [3]. This may have favourable effects on pregnancy rates by reducing potentially damaging products produced by sperm [4][5][6].…”

Fetal bovine serum is associated with polar body degeneration after in vitro maturation of bovine oocytes

“…The sperm-oocyte co-incubation step has been related to an increase in the production of reactive oxygen species (ROS) and other toxic compounds that potentially damage the oocyte (Gianaroli et al, 1996;Agarwal et al, 2006). In addition, the type and source of protein used during IVM has shown to exert a marked effect on DNA degeneration in canine oocytes (Lopes et al, 2011) and also influence the developmental rate of bovine oocytes (Gomez and Diez, 2000).…”