A quantitative assessment of follicle size on oocyte developmental competence

Objective: To quantitatively assess the impact of follicle size on oocyte maturation, fertilization, and embryo quality. Design: Prospective study. Setting: Academic medical center. Patient(s): Couples undergoing ovarian stimulation and in vitro fertilization (IVF). Intervention(S): A total of 235 cycles were monitored prospectively, and 2934 oocytes were collected from five groups of follicle size. Repeated measures multivariate analyses were used to compare the smaller follicle sizes with the lead follicle. Main Outcome Measure(s): Oocyte maturation, fertilization, and embryo quality. Result(s): Compared with the lead follicular group (> 18 mm), the odds of a mature oocyte from a 16 to 18 mm size follicle were 37% and declined progressively with each size. The odds of fertilization of oocytes from follicles 16 to 18 mm in size was 28% less than the lead group and decreased with each size. The rate of polyspermy with conventional insemination was increased for the smaller follicular groups (adjusted odds ratio = 2.37). Follicle size did not predict embryo cell number, but embryos from smaller follicles had a statistically significantly higher fragmentation compared with the lead group. Conclusion(s): The lead follicular group was most likely to have a mature oocyte that was capable of fertilization and best suited for development into a high-quality embryo. The smaller follicles were capable of producing metaphase II oocytes that could fertilize, but at rates approaching only 60% that of the lead follicular group.