Significance of the recovery of fractured-zona oocytes in an in vitro fertilization program

Abstract

Recovery of fractured-zona oocytes (FZOs) from patients undergoing in vitro fertilization and embryo transfer (IVF/ET) has been previously reported. The present study was undertaken to determine the possible influence of different stimulation protocols and retrieval techniques on the incidence of FZOs, to analyze possible causes, and to evaluate the significance of FZOs in terms of IVF/ET results. Four hundred thirty-three cycles in which one or more FZOs were recovered (fractured-zona cycles; FZCs) and 1114 cycles in which FZOs were not obtained (intact-zona cycles; IZCs) were studied. A significantly higher number of follicles was aspirated in FZCs (7.16±3.5) than in IZCs (6.43±3.56), yielding significantly fewer immature oocytes in FZCs (1.58±1.93 vs 1.88±2.16) and a significantly higher number of atretic oocytes in FZCs (2.06±1.36 vs 0.73±1.21). No statistically significant difference was observed when the number of preovulatory oocytes obtained was compared. Nor were statistically significant differences observed as a result of either the type of stimulation [human chorionic gonadotropin (hMG), follicle-stimulating hormone (FSH), or a combination] or the aspiration technique utilized (laparoscopy vs ultrasonically guided puncture). Peripheral estradiol and progesterone and follicular fluid estradiol, progesterone, and androstenedione comparisons showed no significant differences. However, endocrine and morphologic findings (higher follicular androstenedione levels and estradiol/progesterone ratio, degenerated ooplasms) suggested some degree of late oocyte atresia, possibly due to slight hyperstimulation. In an experimental study, two healthy immature oocytes matured in vitro to the metaphase II stage showed degenerative changes in the ooplasm within 20 min after being subjected to mechanical zona pellucida (ZP) damage (mechanical fracture). We conclude that (1) the presence of fracturedzona oocytes in IVF cycles does not impair the pregnancy rates and (2) stimulation-derived oocyte accelerated maturation and subsequent trauma from aspiration determine the fracture of the ZP.