Clinical parameters influencing human zona pellucida thickness.

OBJECTIVES: To assess which clinical parameters influence human oocyte zona pellucida (ZP) thickness. PATIENTS: Sixty-five couples undergoing 75 IVF-ET cycles. MAIN OUTCOME MEASURE: Zona pellucida thickness of 827 oocytes measured 16 to 20 hours after in vitro insemination under inverted light microscope. RESULTS: Zona pellucida thickness was 18.9 +/- 3.8 microns (mean +/- SD) for unfertilized, 16.4 +/- 3.1 microns for fertilized, and 15.1 +/- 2.4 microns for polyspermic oocytes (significantly different). Among our patients, a few underwent two (or even three) IVF-ET cycles, and the mean ZP thickness was, in most cases, not significantly different from one cycle to the other(s). Regression analyses were calculated between ZP thickness and available clinical parameters, i.e., the age of the women, the duration of stimulation, the cumulus maturity, the number of retrieved oocytes, the number of hMG doses, the maximum E2 level, and the follicular volume. A significant linear decreasing relationship exists between the mean ZP thickness of each patient and the maximum E2 level and an increasing one with the hMG dose. Relationships with the other parameters appeared to be nonsignificant. CONCLUSION: The ZP thickness is basically an individual feature that influences the fertilization rate. Nevertheless, it may be influenced slightly by the hormonal treatment during stimulation.