A zona opening procedure for improving in vitro fertilization at low sperm concentrations: a mouse model.

Micromanipulation was used for creating a small opening in the zona pellucida without damaging the ooplasm of oocytes. This was applied in mouse in vitro fertilization as a model for inseminating oocytes with low sperm concentrations. It was found that the opening in the zona did not influence the fertilization rate at 10(5) sperm/ml, but when the sperm concentration was decreased to 10(4)/ml, the oocytes containing the break had a significantly higher fertilization rate and blastocyst development, compared with their intact controls. The zona cracking procedure did not increase parthenogenetic activation nor polyspermic fertilization, although it did promote early hatching of some blastocysts. The birthrate of normal offspring was not affected by exposing oocytes to the zona opening process.