Factors associated with fractured zonae pellucidae in an in-vitro fertilization programme

Oocytes with fractured zonae pellucidae (FZP) were recovered in 43% of cycles in our programme of in-vitro fertilization (IVF) and embryo transfer. Amongst all the recovered oocytes there were 16% FZP oocytes, in which fertilization was precluded. The mean number of punctured follicles and the success rate of oocyte recovery were significantly higher in cycles yielding oocytes with fractured zonae compared with cycles yielding only oocytes with intact zona pellucida oocytes. A damaged zona was found only in healthy mature oocytes and its occurrence was related to the size of the syringe used for follicular aspiration (6.6 versus 20.1% with 10- or 20-ml syringes, respectively, P less than 0.001), and not to the form of ovarian stimulation or follicular characteristics. The proportion of cleaved embryos after the insemination of oocytes with intact zonae was lower in patients also yielding oocytes with fractured zonae (74 versus 86%, P less than 0.001); however, the pregnancy rates after embryo replacement were the same in both groups. We conclude that the technique used for follicle puncture may damage the integrity of zonae pellucidae of healthy mature oocytes. This phenomenon was estimated to be responsible for approximately 15% of failures (16 versus 19 pregnancies per 100 cycles) in our IVF programme.