The Follicular Phase & The Power of Estrogen
How FSH and rising estradiol grow a follicle and rebuild the uterine lining.
Cycle literacy - Cycle Phases & Hormones, about 2 min read
Rising Estrogen and Follicle Growth
Around the start of a period, the pituitary gland releases more Follicle-Stimulating Hormone (FSH). In response, fluid-filled sacs in the ovaries called follicles begin growing. Each follicle holds an immature egg.
As follicles grow, they secrete estradiol—the most potent form of estrogen. Estradiol stimulates cell division in the endometrium, causing the uterine lining to thicken and develop blood vessels in preparation for possible pregnancy.
Physical & Emotional Impacts
Some people notice changes in energy, mood, or skin around this time, but research doesn't show a consistent pattern, and many people notice no difference. Estrogen also interacts with cervical crypts, transitioning cervical fluid from dry or creamy to slippery, fertile fluid as ovulation approaches.
Sources
- Textbook: Speroff's Clinical Gynecologic Endocrinology and Infertility (10th ed.)
- Textbook: Guyton and Hall Textbook of Medical Physiology (15th ed.)
- American College of Obstetricians and Gynecologists: The Menstrual Cycle: Menstruation, Ovulation, and How Pregnancy Occurs
- American College of Obstetricians and Gynecologists: Fertility Awareness-Based Methods of Family Planning