No abstract

In-vitro fertilization by sperm microinjection techniques have been shown to be effective (the birth of one child has resulted), but concerns about the chromosomal normality of embryos derived from this process have been raised. The British Interim Licensing Authority has set, as a pre-condition to the clinical application of sperm microinjection, the chromosomal evaluation of pre-embryos derived by this technique. In this study, we demonstrate that four of 18 (22%) eggs fertilized by sperm microinjection into the perivitelline space are chromosomally abnormal as compared with nine of 30 (30%) fertilized by conventional IVF procedures. These results are not significantly different. In addition, we demonstrate that nine out of 20 couples who did not previously have fertilization in multiple cycles of IVF had between one and three oocytes fertilized by sperm microinjection. These findings demonstrate that sperm microinjection does not increase the incidence of chromosomally abnormal eggs and provide reassurance and support for the clinical implementation of a technique that appears to be effective for the treatment of certain forms of male infertility.

Mouse spermatozoa were obtained from the testis and caput, corpus, and cauda epididymis incubated for 2 h in capacitation medium and a single spermatozoon from the capacitated samples microinjected into the pervitelline space of mature mouse oocytes. Spermatozoa from the testis were unable to fertilize oocytes and few spermatozoa from the caput were capable of fertilization (0-7% depending on the method of preparation). Similar fertilization rates (30-45%) were obtained with spermatozoa with forward progressive motility from the proximal and distal corpus and the cauda epididymis, but those that were vibratory or with local circular motility had significantly reduced fertilizing capacity (6-10%). The capacity of spermatozoa from the different regions of the testis and epididymis to bind to zona-free oocytes followed the same pattern as fertilization rate after microinjection. There was a progressive increase in acrosome reactions after 2 h incubation in capacitation medium in samples obtained from the testis to the cauda epididymis. Maturation of the capacity to bind to the perivitelline membrane and to develop forward progressive motility, rather than the capacity to acrosome react, appears to govern the fertilization of oocytes in which the zona has been bypassed by microinjection. These characteristics are obtained in the proximal segment of the corpus. However, there was evidence that the embryo developmental capacity of oocytes fertilized by spermatozoa from the higher segments of the epididymis is reduced, particularly in oocytes fertilized by caput spermatozoa. These observations suggest that sperm microinjection may have only a limited benefit for improving fertilization rates for men with high epididymal obstructive azoospermia.

Mouse spermatozoa were capacitated and acrosome reacted by incubation for 30 min to 6 h in modified Tyrode's medium (T6) and in cGMP. The fertilization rates of eggs microinjected with a spermatozoon from samples incubated for 30 min, 2 h, and 6 h in T6 and in cGMP were 36%, 34%, 29%, and 43%, respectively. These rates were not correlated to the percentage of acrosome-reacted spermatozoa identified after these treatments. The lack of association could be explained by the selection of an increased proportion of acrosome-reacted spermatozoa actually used for microinjection, particularly in samples incubated for 30 min and 2 h in T6. Both acrosome-intact and acrosome-reacted spermatozoa were identified under the zona in the eggs which failed to fertilize. Fertilized eggs developed at very high rates to the blastocyst stage in vitro.

No abstract

No abstract