Reference — Maternal-Newborn
Menstrual Cycle & Reproductive Hormones Reference
One cycle, two clocks — the ovary maturing and releasing an egg, and the endometrium building up to receive it — run by four hormones. Get this and contraception, PCOS, infertility, and menopause all make sense.
Educational use only. A standard 28-day cycle is used for teaching; real cycles vary in length, mostly in the follicular phase. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
The Cycle, Phase by Phase
| Phase | Ovary | Endometrium | Hormones |
|---|---|---|---|
| Menstrual (days 1–5) | Early follicular | Shedding of the endometrium (menses) | Estrogen & progesterone low (triggers the shed) |
| Follicular / proliferative (days ~6–13) | Follicle matures | Endometrium rebuilds (proliferates) | FSH stimulates the follicle; rising estrogen |
| Ovulation (~day 14) | Egg released | Peak estrogen; receptive mucus | LH SURGE triggers ovulation (estrogen peaks just before) |
| Luteal / secretory (days ~15–28) | Corpus luteum forms | Endometrium secretory, ready for implantation | Progesterone dominant (from corpus luteum); estrogen also present |
The Four Hormones
| Hormone | Source | Role |
|---|---|---|
| FSH (follicle-stimulating hormone) | Anterior pituitary | Stimulates ovarian follicle growth in the follicular phase; rises markedly in menopause as estrogen falls |
| LH (luteinizing hormone) | Anterior pituitary | The mid-cycle SURGE triggers ovulation; supports the corpus luteum |
| Estrogen | Ovarian follicle | Proliferates the endometrium, thins cervical mucus; loss in menopause drives hot flashes, GSM, and bone/CV risk |
| Progesterone | Corpus luteum (then placenta in pregnancy) | Makes the endometrium secretory and maintains it; thickens mucus; a fall (no pregnancy) triggers menses |
Why It Matters Clinically
Contraception works by interrupting this loop — suppressing the FSH/LH surge (no ovulation), thickening mucus, and thinning the endometrium.
The fertile window centers on ovulation; basal body temperature rises after ovulation (progesterone effect) and cervical mucus becomes thin and stretchy near ovulation.
PCOS is chronic anovulation — no LH surge, no corpus luteum, no progesterone, so the endometrium sees unopposed estrogen (cancer risk).
Menopause is follicular depletion — estrogen falls and FSH climbs.
NCLEX Pearls
- ✦The LH SURGE triggers ovulation (~day 14 of a 28-day cycle); estrogen peaks just before it.
- ✦Progesterone (from the corpus luteum) dominates the luteal phase; its fall triggers menstruation if no pregnancy.
- ✦Cycle length varies mostly in the follicular phase; the luteal phase is fairly fixed at ~14 days.
- ✦Ovulation signs: thin/stretchy cervical mucus, a slight BBT rise afterward, and mid-cycle.
- ✦Unopposed estrogen (no progesterone, as in chronic anovulation) → endometrial hyperplasia/cancer risk.
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with American College of Obstetricians and Gynecologists (ACOG) · AWHONN · American Academy of Pediatrics (AAP) — newborn. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →