This chapter presents a study which recognized that the resistance index (RI) of the uterine arteries was around 0.88 until day 13 of a 28-day cycle. The researchers measured the pulsatility index (PI) in 8 women with spontaneous cycles, 20 women undergoing induction of ovulation with clomiphene citrate, and 11 women undergoing controlled ovarian stimulation for in-vitro fertilization with gonadotropin-releasing hormone agonists (GnRH-a), human menopausal gonadotropin (hMG), and human chorionic gonadotropin (hCG). The intraovarian PI showed a gradual decrease from the early follicular (1.05) through the periovulatory (0.99) to the mid-luteal phase (0.85). The detection and quantification of follicular vascularity with pulsed color Doppler is used to predict oocyte recovery rate and hence may be useful in determining the most appropriate time to administer hCG. Oocyte/embryo selection for transfer may benefit from a brief color Doppler examination of each follicle at aspiration and pooling of oocytes with respect to follicles.