THE CORRELATION BETWEEN FOLLICULAR MEASUREMENTS, OOCYTE MORPHOLOGY, AND FERTILIZATION RATES IN AN IN-VITRO FERTILIZATION PROGRAM

Objective: To explore the relationship between follicle size and the morphology of the oocyte-cumulus-corona complex with fertilization rates in stimulated cycles of IVF. Design: Retrospective comparison of measurements and observations of 2,429 oocytes from 215 patients undergoing 324 stimulated IVF cycles. Setting: A large hospital-based IVF program. Main Outcome Measures: Individual follicles were measured by ultrasound before transvaginal aspiration and the size was recorded. The oocyte-cumulus-corona complex from each follicle was examined and classified. The oocytes were checked for evidence of fertilization 17 to 22 hours after insemination. Results: The fertilization rate of all oocytes regardless of morphological type revealed a positive linear correlation with increasing follicle diameter. The fertilization rates of type I oocytes was marginally higher than type II oocytes, controlling for follicle diameter; however, this difference did not achieve statistical significance. Oocytes from follicles with a mean diameter greater than or equal to 16 mm had significantly higher fertilization rates than did oocytes from follicles with a mean diameter less than or equal to 14 mm. Conclusions: Follicle size is a better predictor of fertilization than is morphological characterization of the oocyte-cumulus-corona complex in IVF.