Factors associated with accidental fractures of the zona pellucida and multipronuclear human oocytes following in-vitro fertilization.

A total of 101 multipronuclear oocytes (7.4% of fertilizations) were retrospectively identified in this in-vitro fertilization programme. The use of a manual syringe suction system, instead of an electric pump, to aspirate follicles, was associated with a significant increase in the proportion of oocytes with fractured zonae pellucidae (P less than 0.001), a lower normal fertilization rate (P less than 0.05) and a higher proportion of multipronuclear fertilizations (P less than 0.001). Irrespective of the mode of follicular aspiration, significantly more multipronuclear fertilizations occurred following stimulation with a combination of clomiphene and human menopausal gonadotrophin, than after clomiphene alone (P less than 0.05). It was concluded that the aspiration pressures, created by syringe suction, were more likely to rupture the zona pellucida of some oocytes, while in others it predisposed to an increased multipronuclear fertilization rate.