Factors influencing pregnancy rates following in vitro fertilization and embryo transfer.

In 831 patients having 1533 in vitro fertilization treatments, pregnancy rates were examined in relation to clinical and laboratory factors. Pregnancy rates were significantly affected by the month and year of treatment, the age of the patient, the type of ovarian stimulation, the use of human chorionic gonadotropin, the number of eggs collected, the number of eggs fertilized, the number of embryos developed, and the number of embryos transferred. The most important factors determining pregnancy rates were the number of oocytes collected and the number of embryos transferred. The low pregnancy rate when only one egg was collected raises the problem of how to predict and manage such a patient in a current or future treatment cycle.