Timing of pronuclear development and first cleavages in human embryos after subzonal insemination: influence of sperm phenotype.

The sequential transformations of human sperm nuclei in human eggs after subzonal insemination (SUZI; n = 104) and the influence of sperm defects on this timing were studied. This chronology was compared to that of two control series of zygotes obtained after SUZI with normal spermatozoa (n = 35) and after in-vitro fertilization (IVF) with normal donor spermatozoa (D-IVF; n = 220). Pronuclear formation took place between 4.5 and 10.5 h post-SUZI for 92.8% of the zygotes. They remained visible for 13 h and began to disappear 18.5 h post-SUZI. The timespan 3 h. Zygotes obtained after D-IVF had a similar rate of pronuclear disappearance but approximately 4 h later. The second cell cycle was more rapid for zygotes obtained by D-IVF than by SUZI, but the developmental rate of zygotes obtained by SUZI varied according to sperm phenotypes. For patients with previous unexplained IVF failures (control group with normal spermatozoa), the developmental rate was lower, suggesting the influence of oocyte quality. In conclusion, the end of the first cell cycle of zygotes obtained by insemination under the zona pellucida appears 4 h earlier compared to zygotes obtained after insemination outside the zona pellucida.