Fertilization and cleavage after reinsemination of human oocytes in vitro

The results of reinsemination of 150 morphologically mature oocytes that failed to fertilize within 15 to 20 hours after initial insemination were evaluated. Only 41 oocytes (27.3%) were fertilized after reinsemination, which is significantly lower than the percentage obtained after initial insemination (74%). However, the cleavage rate was not impaired significantly. Polyspermic fertilization was common (17 oocytes, 29.3%). A total of 64 oocytes were transferred. In 18 patients, all of the oocytes that were transferred had been reinseminated; none of these patients conceived. However, of 28 patients who received embryos arising from both initial insemination and reinsemination protocols, 7 conceived (25%). We suggest that the percentage of fertilization is impaired after 22 hours of incubation in vitro and that those oocytes that have fertilized after reinsemination might partly reflect a misjudgment of initial oocyte maturity. Nevertheless, reinsemination is a relatively simple procedure, with no known attributed risk. Therefore, we recommend reinsemination to increase the overall fertilization percentage. Additional studies are needed to establish better methods for assessment of oocyte maturity to evaluate properly the benefit of such reinsemination procedures.