Follicle monitoring, or follicular tracking, uses transvaginal ultrasounds to track the growth of ovarian follicles, which contain eggs. It helps doctors determine the best time for ovulation to time intercourse, intrauterine insemination (IUI), or in vitro fertilization (IVF). The process is crucial for assessing female fertility, determining ovarian reserve, and guiding fertility treatments, especially in cases of infertility or conditions like PCOD.