Role of the cumulus in the selection of morphologically normal sperm and induction of the acrosome reaction during human in vitro fertilization.

This study analyzed the role that the cumulus oophorus may play in the selection of morphologically normal sperm and the induction of the acrosome reaction. Using the triple stain technique, sperm morphology and acrosomal status were compared between sperm that penetrated the cumulus during in vitro fertilization and sperm from outside the cumulus. The mean percentage of morphologically normal sperm in the samples was 54 +/- 2.8 and increased (p < 0.05) to 67 +/- 2.6 within the cumulus. Tapered sperm were significantly decreased (p < 0.05) within the cumulus. The percentage of sperm undergoing the acrosome reaction significantly increased (p < 0.05) from 14.5 +/- 1.5 to 24.5 +/- 1.9 when incubated with a cumulus mass, and further increased to 49 +/- 3.3 when incubated with mature, expanded cumulus tissue containing an oocyte. These data indicate that human cumulus oophorus plays an active role in the selection of morphologically normal sperm, and influences the ability of the sperm to undergo the acrosome reaction.