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 < or = 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 < or = 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).