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What happens to the endometrium during the proliferative phase?

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Diagram of the menstrual cycle showing hormone levels, follicle development, and endometrial changes across 28 days. It highlights menstruation, ovulation, and the follicular and luteal phases, with labeled curves for estrogen, progesterone, FSH, and LH. — menstruation Cyclical changes during a woman's normal ovulatory menstrual cycle.

During the proliferative phase of the menstrual cycle, the endometrium undergoes significant regeneration and growth following the conclusion of menstruation.12

At the start of this phase, the endometrium is thin, with short, straight glands. As an ovarian follicle matures, it secretes the estrogen hormone estradiol. This hormone stimulates the endometrium to proliferate, causing the following changes:2

Increased Thickness: The entire endometrium becomes thicker as it builds up from the residual basal layer.2
Glandular Development: The uterine glands become taller.2
Increased Vascularity: The tissue becomes more vascular, meaning blood flow and the number of blood vessels increase.23

These changes are essential for preparing the uterine lining to potentially receive a fertilized ovum later in the cycle.12