The Ovarian Cycle
A Hormonal Journey Through the 28-Day Rhythm
The menstrual cycle is a conversation between the brain, the ovaries, and the uterus — a monthly rhythm of rising and falling hormones that prepares the body for possible pregnancy. This guide walks through each phase: what the pituitary is signalling, what the ovary is doing, and how the uterine lining responds.
The Cycle at a Glance
A typical cycle averages 21 to 35 days and is driven by a tightly coordinated hormonal cascade. FSH and LH come from the pituitary; estrogen and progesterone come from the ovary. Each hormone rises and falls on cue — and every phase of the cycle reflects that conversation.
Four phases, four hormones, one rhythm — every cycle is the same choreography playing out inside a unique body.
- ·Follicular phase (Days 1–13) — FSH grows follicles; estrogen builds the lining.
- ·Ovulation (Day 14) — an LH surge releases the egg.
- ·Luteal phase (Days 15–25) — the corpus luteum makes progesterone.
- ·Premenstrual (Days 26–28) — hormones fall; the lining sheds if no pregnancy.
Follicular Phase — Days 1 to 13
The pituitary releases FSH (follicle-stimulating hormone), which recruits a cohort of ovarian follicles to begin maturing. Within a few days, one becomes dominant — the others regress. The dominant follicle produces estrogen, which quietly rebuilds and thickens the uterine lining after menstruation.
| System | What's happening |
|---|---|
| Pituitary | FSH rises to stimulate follicle growth. |
| Ovary | Many follicles grow; one becomes dominant. |
| Uterus | Menstruation ends; the lining enters the proliferative phase and thickens under estrogen. |
Ovulation — Day 14
As estrogen from the dominant follicle peaks, it flips the pituitary from suppression to a burst — the LH surge (with a smaller rise in FSH). Within 24 to 36 hours, LH ruptures the follicle and the mature egg is released.
The Fertile Window
Cervical mucus around ovulation becomes clear and stretchy — the classic 'egg-white' consistency — designed to help sperm survive and travel. This is when conception is most likely.
Luteal Phase — Days 15 to 25
The now-empty follicle transforms into the corpus luteum, a temporary endocrine gland that secretes progesterone (with continued estrogen). Progesterone makes the uterine lining thick, glandular, and rich — ready to support implantation. LH falls back down and stays low.
| System | What's happening |
|---|---|
| Pituitary | LH and FSH stay low after ovulation. |
| Ovary | The empty follicle becomes the corpus luteum, producing progesterone. |
| Uterus | The lining enters the secretory phase — glandular, receptive, well-vascularized. |
If No Pregnancy — Days 26 to 28
Without an implanting embryo signalling with hCG, the corpus luteum has a fixed lifespan of about 10 to 14 days. It regresses into a small scar called the corpus albicans, and progesterone and estrogen fall sharply.
That hormone withdrawal is what starts the next cycle — the lining loses its support, breaks down, and sheds as menstruation. FSH begins to rise again, and a new cohort of follicles is recruited.
If Pregnancy Occurs
- ·The implanting embryo produces hCG.
- ·hCG rescues the corpus luteum from regression.
- ·Progesterone stays high, the lining is maintained, and menstruation doesn't occur.
A General Reference
Cycle length, hormone levels, and symptoms vary between individuals — and across seasons of life. This guide is a general educational reference, not a personal readout. When something feels off, a clinician and a targeted workup can tell you what's going on.