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The effect of preinsemination interval upon fertilization of human oocytes in vitro.

A correlation between oocyte maturity, duration of preinsemination interval (PII) and fertilization rate in vitro has been suggested. Therefore, delayed insemination is being widely practised in many IVF centres. The purpose of this study was to investigate prospectively the effect of PII upon the fertilization rate in vitro. A total of 1474 oocytes were inseminated following incubation for between 30 and 540 min. The duration of the PII was determined randomly. It was found that neither fertilization rate (on average 46.9%) nor pregnancy rate (20.4%, calculated per embryo transfer) were affected by PII for any given degree of oocyte-cumulus maturity. The ability to inseminate oocytes at any time (within 9 h following egg collection) to the convenience of the biologist further simplifies the technology of IVF.