High frequency of defective sperm-zona pellucida interaction in oligozoospermic infertile men

BACKGROUND: The ability of sperm to interact with the zona pellucida (ZP) plays a critical role during the process of human fertilization. The aim of this study is to determine frequency of defective sperm-ZP interaction in oligozoospermic infertile men. METHODS: Sperm-ZP binding assays and the ZP-induced acrosome reaction (AR) were performed in 72 infertile men with a sperm concentration <20XIOI/ml. Oocytes that had previously failed to fertilize in a clinical IVF programme were used for the tests. Motile sperm (2X10(6)/ml) selected by swim-up from each semen sample were incubated with four oocytes for 2 h. The number of sperm bound per ZP and the ZP-induced AR were assessed. Under these conditions, an average of ≤40 sperm bound/ZP was defined as low sperm-ZP binding and a ZP-induced AR ≤16% was defined as low ZP-induced AR. RESULTS: In the 72 oligozoospermic men, 28% (20/72) had low sperm-ZP binding. Of those with normal sperm-ZP binding, 69% (36/52) had low ZP-induced AR. Overall, 78% (56/72) had either low ZP-binding or normal ZP binding but low ZP-induced AR. This means that only 22% (16/72) had both normal sperm-ZP binding and normal ZP-induced AR. CONCLUSION: Oligozoospermic men have a very high frequency of defective sperm-ZP interaction, consistent with their low natural fertility or low fertilization rate in conventional IVF. Infertile couples with oligozoospermic semen should be treated by ICSI rather than by conventional IVF.