The Menstrual Cycle & Hormones
Know the four phases and which hormone drives each — ovulation is the hinge.
The average menstrual cycle is about 28 days (normal range 21–35 days), with menstrual flow lasting 2–7 days. Menarche (the first period) usually occurs around age 12. The cycle is controlled by a feedback loop among the hypothalamus, pituitary, and ovaries.
- Menstrualdays 1–5
- The endometrium sheds (the period) because hormone levels dropped.
- Follicular / proliferative~days 6–13
- FSH matures an ovarian follicle; rising estrogen rebuilds (thickens) the endometrium.
- Ovulation~day 14
- A surge of LH releases the egg from the follicle. Fertile window.
- Luteal / secretory~days 15–28
- The corpus luteum secretes progesterone, preparing the lining. If no pregnancy, progesterone falls and menses begins.
The single most-tested cycle fact: a surge of LH triggers ovulation around day 14. Estrogen dominates the first half (builds the lining) and progesterone dominates the second half (maintains it). When progesterone drops, the period starts.
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Amenorrhea
No periods — and the first thing to rule out is pregnancy.
- Primary amenorrhea: no menstruation by about age 15 (with otherwise normal development).
- Secondary amenorrhea: no periods for 3 or more months in someone who previously had regular cycles.
- Most common cause of secondary amenorrhea is pregnancy — always check a pregnancy test first.
- Other causes: significant stress, excessive exercise or very low body fat (athletes), eating disorders, PCOS, thyroid disease, and menopause.
When a previously regular client misses periods, the priority assessment is a pregnancy test — pregnancy is the most common cause of secondary amenorrhea. Only after pregnancy is excluded do you investigate other causes like stress, low body fat, thyroid problems, or PCOS.
Dysmenorrhea
Painful periods — prostaglandins are the culprit, so NSAIDs are first-line.
- Primaryno underlying disease
- Caused by prostaglandins. Cramping lower-abdominal/pelvic pain with menses, often in younger women.
- Secondaryunderlying condition
- Caused by endometriosis, fibroids, PID. Treat the cause; often appears later or worsens over time.
- NSAIDs (ibuprofen, naproxen) are first-line — they block prostaglandins. Most effective when started just before or at the onset of the period; take with food.
- Heat (heating pad), regular exercise, and combined hormonal contraceptives also reduce pain.
Primary dysmenorrhea is caused by prostaglandins that make the uterus contract — so NSAIDs (not acetaminophen) are first-line because they inhibit prostaglandin production. Teach the client to start them at the first sign of the period and take them with food.
Abnormal Uterine Bleeding
Know the terms — heavy vs between-cycle bleeding — and what to report.
- Menorrhagia
- Heavy or prolonged menstrual bleeding (e.g., soaking a pad/tampon hourly, clots, periods over 7 days).
- Metrorrhagia
- Bleeding between periods (intermenstrual bleeding).
- Oligomenorrhea
- Infrequent periods (cycles longer than ~35 days).
- Postmenopausal bleeding
- Any bleeding after menopause — always reported (rule out endometrial cancer).
- Common causes include hormonal imbalance, uterine fibroids, polyps, and (in older or postmenopausal women) malignancy.
- Teach clients to track bleeding (pad counts) and to report heavy bleeding, bleeding between periods, or any bleeding after menopause.
Any vaginal bleeding after menopause must be reported and evaluated — it can be a sign of endometrial cancer. The same urgency applies to very heavy bleeding (soaking a pad an hour) or bleeding with dizziness, which signals significant blood loss.
PMS & PMDD
Cyclic symptoms in the luteal phase that resolve once the period starts.
- Premenstrual syndrome (PMS): physical and emotional symptoms in the luteal phase (the days before menses) — bloating, breast tenderness, irritability, fatigue, mood changes — that resolve with the onset of the period.
- Premenstrual dysphoric disorder (PMDD): a severe form with disabling mood symptoms (marked irritability, depression, anxiety) that impair daily functioning.
- Management: lifestyle measures (regular exercise, reduced caffeine/salt/alcohol, stress management), SSRIs (for PMDD or significant mood symptoms), and combined hormonal contraceptives.
Both PMS and PMDD occur in the luteal phase (after ovulation, before the period) and resolve once menses begins. That cyclic pattern — symptoms tied to the second half of the cycle — is what distinguishes them from other mood or physical conditions.
Endometriosis
Endometrial tissue in the wrong place — cyclic pain and a leading cause of infertility.
Endometriosis is the growth of endometrial-like tissue outside the uterus (ovaries, tubes, pelvic structures). It responds to the cycle's hormones and bleeds each month, causing inflammation, scarring, and adhesions.
- Classic symptoms: cyclic pelvic pain, painful periods (dysmenorrhea), pain with intercourse (dyspareunia), and infertility.
- Treatment: NSAIDs for pain; hormonal suppression of the cycle — combined contraceptives or GnRH agonists (leuprolide); surgery (laparoscopy) to remove lesions in some cases.
- Pregnancy and menopause tend to relieve symptoms (less cyclic hormone stimulation).
Think endometriosis when a client has worsening dysmenorrhea, pelvic pain, painful intercourse, and trouble conceiving. Because the tissue is hormone-driven, treatment aims to suppress the cycle (hormonal therapy) — and it is a common cause of secondary dysmenorrhea.
Polycystic Ovary Syndrome (PCOS)
Irregular periods + excess androgens + insulin resistance.
PCOS is a hormonal disorder defined by a combination of irregular or absent periods, signs of excess androgens, and often polycystic ovaries on ultrasound.
- Signs: irregular/absent menses, hirsutism (excess hair), acne, weight gain, and infertility (from lack of ovulation).
- Insulin resistance is central — raising the long-term risk of type 2 diabetes. Unopposed estrogen also raises the risk of endometrial cancer.
- Management: weight loss and exercise (first-line, improves ovulation), metformin for insulin resistance, combined hormonal contraceptives to regulate cycles, and letrozole (commonly first-line) or clomiphene to induce ovulation when pregnancy is desired.
Remember PCOS as the trio of irregular periods, androgen excess (hirsutism/acne), and insulin resistance. The first-line intervention is weight loss and exercise, which can restore ovulation; metformin and combined contraceptives are common medical therapies.
? A client with PCOS wants to get pregnant — which medication is used to induce ovulation?
Menopause, Fibroids & TSS
Estrogen decline at midlife, plus two more high-yield conditions.
Menopause
- Menopause = no menstrual period for 12 consecutive months; average age about 51. Perimenopause is the transition before it, with irregular cycles.
- Caused by declining estrogen → hot flashes, night sweats, vaginal dryness, mood changes, sleep disturbance, and over time bone loss (osteoporosis) and increased cardiovascular risk.
- Management: lifestyle (layered clothing, avoid triggers), vaginal lubricants/moisturizers for dryness, calcium, vitamin D, and weight-bearing exercise for bone health, and hormone therapy or SSRIs/SNRIs for bothersome hot flashes (weigh risks/benefits).
Uterine Fibroids (Leiomyomas)
- Benign smooth-muscle tumors of the uterus; very common. May cause heavy bleeding (menorrhagia), pelvic pressure/fullness, and may shrink after menopause.
Toxic Shock Syndrome (TSS)
- Rare, life-threatening; linked to leaving tampons (or other devices) in too long.
- Teaching: change tampons every 4–8 hours, use the lowest absorbency needed, alternate with pads (especially overnight), and wash hands.
- Report: sudden high fever, sunburn-like rash, vomiting/diarrhea, dizziness/low blood pressure, muscle aches — remove the tampon and seek care immediately.
Falling estrogen accelerates bone loss, so menopausal clients are at higher risk for osteoporosis and fractures. Teach calcium, vitamin D, and weight-bearing exercise, and (for TSS prevention) to change tampons every 4–8 hours and use the lowest absorbency needed.
Frequently Asked Questions
Common student questions on this topic.
What are the phases of the menstrual cycle?
What is the difference between primary and secondary amenorrhea?
How is dysmenorrhea (painful periods) treated?
What is endometriosis and what are its main symptoms?
What are the signs of polycystic ovary syndrome (PCOS)?
What teaching helps prevent toxic shock syndrome (TSS) with tampon use?
Quick-Reference Cheatsheet
Every key point from this guide on a single printable page.
Reproductive Health & Menstrual Disorders Cheatsheet
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