All patients will be instructed to call the clinic on day 1 of menses. If menses begins before 6 pm, that day will be considered day 1. If menses begins after 6 pm, the next day will be considered day 1. Women randomized to the day 1 treatment group will be instructed to begin ovarian stimulation therapy (Gonal-f, Serono Canada) on day 1 and visit the clinic to undergo their first transvaginal ultrasound examination on day 2. Women randomized to the day 4 treatment group will be instructed to begin ovarian stimulation on day 4 and visit the clinic on day 4 for their first transvaginal ultrasound examination. Ultrasound examinations will be performed to determine the number of follicles developing in the ovaries. Ultrasound examinations will continue every 2-4 days for each woman, as per the normal standard of care. Blood will be drawn intermittently during stimulation to determine serum concentrations of estradiol-17B. Each participant will be asked to perform a home urine pregnancy test before taking their first dose of study medication. If a woman is found to be pregnant, she will be withdrawn from the study.