The influence of the site of sperm deposition and mode of oolemma breakage at intracytoplasmic sperm injection on fertilization and embryo development rates

Abstract

The aims of this study were to examine, in a prospective, controlled way, the effect of the sperm deposition site in the oocyte and the mode of oolemma breakage in intracytoplasmic sperm injection (ICSI) on fertilization and embryo development rates. In the first trial (100 cycles in total), the spermatozoa were deposited further from the meiotic spindle (polar body at the 12 o'clock position) in half of the oocytes (n = 649), while in the other half (n = 605) the spermatozoa were deposited nearer to the meiotic spindle (polar body at the 6 o'clock position). In the second trial (6860 oocytes in 624 cycles), five different modes of membrane breakage (the reaction of the oolemma to the penetrating injection needle) at the moment of injection were noted: oolemma breakage, type A pricking once, no suction (n = 1401); type B, pricking once, small suction (n = 2761); type C, pricking once, long suction (n = 2310); type D, pricking twice or more, no or small amount of suction (n = 259); and type E, pricking twice or more, long suction (n = 129). No differences were observed between the 12 and 6 o'clock positions in the survival rate (90 and 90% respectively) and in the normal fertilization rates (78 and 77% respectively). Significantly more transfer quality embryos (< or = 50% fragmentation) were obtained in the 6 o'clock position group (83%) than in the 12 o'clock position group (79%). In the second trial, significantly lower survival rates were noted after membrane breakage type A (82%) than after breakages of types B, C, D and E (93, 92, 88 and 88% respectively). There were no significant differences present in the normal fertilization rates (70, 72, 70, 71 and 73% for types A-E respectively), but significantly more freeze quality embryos (< or = 20% fragmentation) were obtained after injection B (65%) than after injection types A, C, D and E (59, 61, 55 and 51% respectively). In conclusion, the site of sperm deposition in the oocyte does not influence the normal fertilization rate but does affect the embryo development rate. Furthermore, the mode of membrane breakage does not influence the normal fertilization rate but does affect oocyte survival and embryo development rates.

Sperm retention site and its influence on cleavage rate and early development following intracytoplasmic sperm injection

“…It has been suggested that injecting sperm closer to the site of the spindle may improve outcome (8,10). Nagy et al suggested that cleavage would be facilitated when the sperm was injected closer to the spindle (11). Although the sample size in this study was quite small, our results may support their findings.…”

Developmental capacity and pregnancy rate of tetrahedral- versus non-tetrahedral-shaped 4-cell stage human embryos

“…This model of early asymmetry was extrapolated to the human and supported by the polarized distribution of proteins such as Leptin and STAT3 in the oocyte, their differential distribution between the blastomeres at the 4-cell stage and later on between the ICM and TE [6] and by the reciprocal expression of OCT-4 and βhCG transcripts at the 4-cell stage [11,12]. Indirect evidence of oocyte polarity in the human was given by the correlation between the site of sperm deposition in the oocyte and the embryo development rate [13]. The early interpretation of Edwards's model that the generated differences would be deterministic proved wrong as early cells can change their fate after repositioning [14].…”

Estimating zona pellucida hardness under microinjection to assess oocyte/embryo quality: Analytical and experimental studies

“…Although the efficiency of ICSI has been clearly demonstrated [2,4,5], this procedure is typically associated with the degeneration of a significant percentage of treated oocytes [2,3,6,7]. The main cause of this degeneration remains unclear.…”

“…Some researchers, such as Dumoulin et al (2001) and Ebner et al (2003) have speculated that severe mechanical stress during the unusual injection procedure may be responsible for oocyte degeneration [8,9]. However, on certain occasions, some oocytes show deviations from the presumed optimal ICSI due to a possible impairment in the elasticity of the ZP, which would normally allow the formation of a distinct funnel prior to puncture [3,6]. This is characterized by either sudden breakage or delayed penetration of the zona and is likely to result in increased gamete damage [3,6,8,9].…”

“…However, on certain occasions, some oocytes show deviations from the presumed optimal ICSI due to a possible impairment in the elasticity of the ZP, which would normally allow the formation of a distinct funnel prior to puncture [3,6]. This is characterized by either sudden breakage or delayed penetration of the zona and is likely to result in increased gamete damage [3,6,8,9].…”