Follicle size and implantation of embryos from in vitro fertilization

To determine the effect of increased follicle size at the time of hCG administration on the outcome of in vitro fertilization (IVF). Fifty women immediately before and 50 immediately after a protocol change were reviewed retrospectively. The criterion for hCG administration was changed from a leading follicle size of at least 17 mm to one of at least 20 mm (average of two dimensions). Changes in follicle size and number, oocytes recovered, fertilization rate, embryo development, implantation rate, and pregnancy rate were examined. Women over 40 years of age, those undergoing intracytoplasmic sperm injection, and those whose stimulation did not include GnRH agonists were excluded. The number of large follicles increased, but peak estradiol concentrations and number of oocytes recovered did not differ when hCG was administered at a follicular size of at least 20 mm. The numbers of oocytes fertilized, embryos replaced, and embryos cryopreserved were not statistically different. The percentage of cleaved fertilized oocytes was greater and the degree of embryo fragmentation smaller when hCG was administered at an increased follicular size. The implantation rate was higher and clinical and ongoing pregnancy rates tended to be higher when hCG was administered at a larger follicle size. The administration of hCG at a larger follicle size appears to have a beneficial effect on the outcome of IVF. Embryo quality—as reflected by decreased fragmentation, increased cleavage, and increased implantation rate—appears to be improved when hCG is delayed until two or more follicles reach at least 20 mm in diameter.