The menstrual cycle is controlled by the hypothalamic–pituitary–ovarian axis. Gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The ovary and the endometrium change in parallel.

• The luteal phase is relatively constant (about 14 days); differences in cycle length come from the follicular phase. In a 35-day cycle, ovulation occurs around day 21 — count back 14 days from the expected next period.
• If no pregnancy occurs, the corpus luteum regresses, progesterone falls, and the lining sheds.
• Normal adult cycle: about 24–38 days, bleeding up to 8 days.
• Basal body temperature rises about 0.3–0.5 °C (0.5–1 °F) after ovulation because of progesterone.

Common disorders

Menstrual history

• Age at menarche, cycle length, duration, last menstrual period (LMP), regularity
• Quantify bleeding: number of pads or tampons soaked, need to change every 1–2 hours, clots larger than about 2.5 cm (1 inch), flooding at night, days missed from school or work
• Pain: timing with menses, severity, response to analgesics, dyspareunia, bowel symptoms

Anemia and hemodynamic status (priority with heavy bleeding)

• Fatigue, dizziness, pallor, dyspnea on exertion, tachycardia, orthostatic hypotension, pica

Other findings

• PCOS: irregular cycles, hirsutism, acne, central obesity, acanthosis nigricans
• Hyperprolactinemia: galactorrhea, headache, visual field loss (pituitary tumor)
• Hypothalamic amenorrhea: low body mass index, restrictive eating, stress fractures
• PMS/PMDD: breast tenderness, bloating, weight gain, irritability, depressed mood — screen for suicidal thoughts in PMDD

• Pregnancy test (urine or serum hCG) first for any reproductive-age client with amenorrhea or abnormal bleeding
• CBC and ferritin with heavy bleeding; coagulation studies and von Willebrand evaluation when heavy bleeding began at menarche or there is a bleeding history
• TSH, prolactin; FSH/LH and estradiol (ovarian insufficiency); total testosterone for hyperandrogenism
• Transvaginal pelvic ultrasound — first-line imaging for structural causes (polyps, fibroids, adenomyosis) and ovarian morphology
• Endometrial biopsy — for AUB in clients 45 years and older, or younger with prolonged unopposed estrogen exposure (obesity, PCOS) or failed treatment
• Symptom diary for at least 2 cycles to confirm the luteal timing of PMS/PMDD
• PCOS diagnosis (Rotterdam criteria, used by the 2023 international guideline): 2 of 3 — ovulatory dysfunction, clinical or biochemical hyperandrogenism, polycystic ovarian morphology on ultrasound (or high anti-Müllerian hormone in adults), after excluding other causes
• Female athlete: bone density (DXA) after about 6 months of amenorrhea or with stress fractures

Procedures — hysteroscopic removal of polyps or submucosal fibroids; endometrial ablation for heavy bleeding when childbearing is complete; hysterectomy as definitive therapy.

Acute heavy bleeding with instability — IV access, fluids, type and crossmatch, transfusion as needed; high-dose IV or oral hormones or tranexamic acid per provider; rarely uterine tamponade or curettage.

Listed in priority order.

1. Assess hemodynamic status with heavy bleeding — vital signs (pulse, blood pressure, orthostatic changes), level of consciousness, pad count or weight (1 g ≈ 1 mL), hemoglobin; report tachycardia, hypotension, or soaking a pad every hour for 2 or more hours
2. Safety with anemia — rise slowly (sit before standing), assist with ambulation, fall precautions
3. Rule out pregnancy before tests or drugs in amenorrhea or AUB
4. Pain management — scheduled NSAIDs as ordered, heat to the lower abdomen or back, exercise, rest; reassess pain response
5. Administer and monitor drugs — check contraindications before hormonal therapy (smoking, VTE, migraine with aura, blood pressure); give iron correctly
6. Emotional support and screening — PMDD: screen for depression and suicidal ideation; PCOS: body image, weight stigma, fertility worries
7. Refer — gynecology, endocrinology, dietitian, sports medicine, or mental health as indicated

• Menstrual hygiene
  • Change pads when soaked; change tampons every 4–8 hours and never leave one in longer than 8 hours; use the lowest absorbency needed; alternate with pads at night if preferred; wash hands before and after insertion
  • Toxic shock syndrome (TSS) warning signs: sudden high fever, vomiting, diarrhea, sunburn-like rash, dizziness, or low blood pressure — remove the tampon and seek care immediately
  • Menstrual cups: empty and clean per manufacturer; the same TSS precautions apply
  • Do not douche; avoid scented pads and feminine sprays
• Dysmenorrhea: start NSAIDs at the first sign of pain or bleeding; regular aerobic exercise and heat help; report pain that worsens over time, pain not relieved by NSAIDs, or pain with intercourse — these suggest secondary causes
• PMS: keep a symptom diary; limit salt (reduces bloating), caffeine, alcohol, and refined sugar; small frequent meals with complex carbohydrates; regular aerobic exercise; adequate sleep and stress reduction; calcium-rich diet
• PCOS: modest weight loss (5–10%) can restore ovulation; balanced diet and regular exercise to improve insulin resistance — no single diet is required; long-term risks include diabetes, dyslipidemia, sleep apnea, and endometrial hyperplasia, so regular screening matters
• Fertility awareness: ovulation occurs about 14 days before the next period, not always on day 14
• Athletes: missed periods are not a normal effect of training; adequate energy intake, calcium, and vitamin D protect bone
• Iron: continue for about 3 months after hemoglobin normalizes to refill stores; keep out of reach of children (overdose is dangerous)

• Follicular phase: FSH matures follicles, estrogen builds a proliferative lining; LH surge triggers ovulation
• Luteal phase: corpus luteum progesterone creates a secretory endometrium; it lasts about 14 days
• Ovulation ≈ 14 days before the next menses
• Amenorrhea → pregnancy test first
• Heavy bleeding: assess vital signs and anemia first; quantify pads
• Primary dysmenorrhea = prostaglandins, no pathology → NSAIDs first-line
• PMS: limit salt, caffeine, alcohol; exercise; PMDD first-line drug = SSRI
• PCOS: irregular cycles + hirsutism/acne + insulin resistance → weight management, metformin, hormonal contraceptives
• Prolactinoma → dopamine agonist (cabergoline, bromocriptine)
• Tampons: lowest absorbency, change every 4–8 h, never over 8 h (TSS)
• Athlete amenorrhea → low bone density and stress fractures
• Iron: do not take with dairy, calcium, or antacids