Factors leading to tripronucleate eggs during human in-vitro fertilization.

Four-hundred-and-ninety-one oocytes were collected from 142 successive patients attending for in-vitro fertilization. The systematic observation of pronuclei between 14 and 18 h after insemination revealed 27 cases of tripronucleate eggs among 391 fertilized eggs (6.9%), which corresponds to rates generally reported in the literature. The following parameters were analysed in relation to the incidence of these eggs: aetiology of infertility, follicular response to hormonal stimulation, type of ovulatory stimulus, sperm count and motility and the incidence of fertilization. Only fertilization rates and concentration of motile spermatozoa in the insemination medium were found to be correlated with tripronucleate eggs, confirming that the condition is predominantly due to polyspermy. Comparisons with data from animals, and measures aimed at preventing polyspermy are suggested.