Optimized hormonal stimulation is critical for production of viable embryos and establishment of subsequent implantation.

PurposeTo investigate the effects of follicle number and size at the time of hCG administration, and ovarian stimulation length on the outcome of in vitro fertilization and pregnancy rate.MethodsDuring the ovarian stimulation regimen, the follicular number and size were determined by transvaginal ultrasonographic examination. Ovulation was induced as early as three or more follicles were at least 16 mm in their greatest diameter.ResultsThe fertilization rates were significantly increased with the longer length of stimulation (10-12 days: 75.4% and 13-16 days: 83.2%). However, no significant differences in the chemical pregnancy, clinical pregnancy, and implantation rates were found between 10-12 days (53.7%, 43.9%, and 21.8%) and 13-16 days (50.0%, 43.8%, and 23.4%) of stimulation. There were no significant differences in fertilization and chemical pregnancy rates between two groups with > or = and <18 follicles in the ovaries on the day of hCG (human chorionic gonadotrophin) administration. However, the clinical pregnancy and implantation rates (47.2% and 26.0%) in the group with or =18 follicles, respectively.ConclusionsExcessive and rapid ovarian stimulation appears to decrease the survival of embryos at later stages after transfer. The advantage of prolonged stimulation may outweigh the potential adverse effects in some patients.