Fertilization of human oocytes by microinjection of human sperm aspirated from the caput epididymidis of an individual with obstructive azoospermia.

Aspiration of spermatozoa from the caput region of the epididymis was performed, due to obstructive azoospermia. When all inseminated oocytes failed to fertilize in vitro, immotile spermatozoa were microinjected into the perivitelline space to achieve fertilization. Of six oocytes microinjected, one exhibited two normal pronuclei and two polar bodies and was subsequently transferred to a fallopian tube of the wife. One oocyte arrested at syngamy, while two additional oocytes cleaved to four cells each. The remaining two were damaged during microinjection. Although the patient did not conceive, this report provides evidence that (1) spermatozoal motility is not required for successful pronuclear formation when microinjection is performed, and such immotile sperm are not necessarily "dead," and (2) this further corroborates that caput epididymal spermatozoa can participate in the subzonal events of fertilization and that, in the human, exposure of spermatozoa to the distal epididymal milieu may not be a requisite to achieve fertilizing capacity.