Relationship of subnormal semen parameters and subsequent zona pellucida thinning following in vitro fertilization.

Infertility due to male factor has been associated with reduced implantation rates despite normal fertilization. The mechanism responsible for lower pregnancy rates is not known. One cause of failure to achieve pregnancy despite transfer of embryos is impairment of zona pellucida (ZP) thinning, which inhibits the embryo from hatching despite initial cell cleavage. This study was designed to evaluate whether there is an association between the ability of the ZP to thin, as measured by ZP thickness on day of transfer, and subnormal semen parameters. Significant differences in ZP thickness (p < 0.05, Kruskal-Wallis) were noted according to median concentration of sperm, total motile sperm, and motile density in that these values were the highest in the group of embryos with the thinnest zona pellucida and lowest in the group with the thickest zona pellucida. Thus, some factor may be missing from sperm from subnormal specimens that normally assists in zona thinning.