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

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 (less than or equal to 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 (less than or equal to 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.