The Follicular Phase is the first part of the menstrual cycle, beginning on the first day of menstruation and lasting until ovulation. During this phase, the pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the growth of ovarian follicles. Each follicle contains an egg, and typically, one follicle becomes dominant and matures while the others regress. As the follicles develop, they produce estrogen, a hormone that helps thicken the uterine lining in preparation for a potential pregnancy. The rising estrogen levels also signal the pituitary gland to reduce FSH production and increase luteinizing hormone (LH), leading up to ovulation, which marks the end of the follicular phase.