['To determine if the timing of the onset of pituitary desensitization and ovarian suppression using follicular phase leuprolide acetate (LA) is associated with in vitro fertilization-embryo transfer (IVF-ET) success for pregnancy.', 'Retrospective series of IVF patients undergoing pituitary desensitization and ovarian suppression before beginning controlled ovarian hyperstimulation for IVF-ET.', 'Tertiary infertility practice.', 'Seventy-eight women for 80 cycles began LA on day 1 of their menstrual cycle. After 11 days of LA, 47 (59%) cycles in group I had suppressed serum estradiol (E2) levels less than 40 pg/mL, in contrast to 33 (41%) cycles in group II not adequately suppressed, thereby requiring additional days to achieve suppression.', 'Controlled ovarian hyperstimulation was started when patients were satisfactorily suppressed, i.e., E2 less than 40 pg/mL.', 'Mean E2 response, ampules of human menopausal gonadotropin, cancellation rates, number of oocytes retrieved, fertilization rates, and pregnancy rates (PRs) per cycle were examined between groups I and II.', 'Group I demonstrated a greater mean E2 response on the day of human chorionic gonadotropin 1,735 pg/mL versus 1,470 pg/mL (P = 0.008), a greater fertilization rate 64% versus 55% (P = 0.02), and a higher PR per cycle 34% versus 12% (P = 0.036) compared with group II.'] Is early pituitary desensitization and ovarian suppression with leuprolide acetate associated with in vitro fertilization-embryo transfer success?