EFFECT OF FOLLICULAR SIZE ON OOCYTE RETRIEVAL, FERTILIZATION, CLEAVAGE, AND EMBRYO QUALITY IN IN-VITRO FERTILIZATION CYCLES - A 6-YEAR DATA-COLLECTION

Objective: To determine the effect of follicular size, including the size of the leading follicle, on oocyte retrieval, fertilization, cleavage, and embryo quality in IVF cycles based on a large data collection. Design: Retrospective analysis of 1,109 IVF cycles between 1987 and 1993 at the Hospital of the University of Pennsylvania including 606 patients ranging in age from 23 to 49 years. Results: Follicles with a volume less than or equal to 1 mL show a significantly lower oocyte recovery rate than follicles with a volume of >1 mL. The highest recovery rate (83.5%) was found in follicles with a volume of 3 to 4 mL. Above a follicular volume of 7 mL, the oocyte recovery drops below that observed for follicles between 1 and 7 mL. Fertilization and cleavage rates were also higher in oocytes obtained from follicles >1 mL compared with follicles less than or equal to 1 mL. Although fertilization rates were fairly stable above volumes of 1 mL, cleavage rates continued to rise to a peak percentage of 92% with volumes between 6 and 7 mL. Leading follicle size did not have an effect on fertilization and cleavage rates of cohort oocytes. Embryo quality was not influenced significantly by follicular volume. Conclusion: Based on this evaluation of a large number of follicles, follicular size is a useful indicator of oocyte recovery, fertilization, and cleavage in IVF cycles. For optimal results, the follicular fluid volume in gonadotropin- and hCG-stimulated cycles should be >1 mL, which corresponds to a follicle diameter of >12 mm, and not larger than 7 mL (24 mm). For timing of hCG administration, the number of adequate size follicles appears to be more important than the size of the leading follicle(s).