Cycle × body · 6 min
Irregular cycle — when it's physiology and when it's worth checking
A "regular cycle" is not 28 days on the dot. Per FIGO (International Federation of Gynecology and Obstetrics), a cycle is normal if it lasts 24–38 days, with cycle-to-cycle variation under 7–9 days. Anything outside that range is worth checking — but "worth checking" doesn't mean "something is wrong".
When irregularity is physiological
- First 2–3 years after menarche — the hormonal axis is still stabilizing.
- Perimenopause (typically 40+) — estrogen fluctuations and skipped ovulations make cycles shorten and lengthen erratically.
- First 6 months postpartum, especially with breastfeeding.
- After stopping hormonal contraception — it can take 3–6 months for rhythm to return.
- After significant weight change, intense training, or stress — the hypothalamic-pituitary axis responds to energy deficit.
When irregularity is a signal
A gynecology or endocrinology consult is warranted if:
- Cycles are consistently shorter than 21 days or longer than 35.
- No menstruation for 3 consecutive months (not pregnant, not breastfeeding, not menopausal).
- Bleeding is very heavy (changing pad/tampon more than every 2 hours) or lasts >7 days.
- Intermenstrual or post-coital bleeding appears.
- Adult acne, hirsutism, or stubborn weight gain — possible PCOS.
- Hair loss, cold intolerance, fatigue — possible hypothyroidism.
Most common causes
- Polycystic ovary syndrome (PCOS) — the most common cause of long cycles in reproductive age.
- Hypo- or hyperthyroidism — shifts cycle rhythm before classic symptoms appear.
- Hyperprolactinemia — can suppress ovulation.
- Functional hypothalamic amenorrhea (FHA) — with energy deficit, training, food restriction.
- Perimenopause.
- Chronic stress — shorter and stronger than expected; the HPA axis is sensitive.
What to bring to the appointment
The first question will be about the length of recent cycles. Without a record, most people answer "30, maybe 35, I don't really remember". With a tracking app, the conversation starts with specifics: the last 6 cycles were 32, 41, 28, 35, 47, 29 days. That changes the diagnostic direction immediately.
What NOT to do on your own
- Don't "regulate hormones" with supplements before diagnostics — many (e.g., chasteberry) actually affect the cycle and can mask disease symptoms.
- Don't assume contraception will "regulate" the cycle — it switches it off, giving withdrawal bleeds. That may be a solution, but it's not a diagnosis.
- Don't wait two years on a missing period — any amenorrhea lasting >3 months deserves a workup.
What actually helps
2–3 months of logging cycle length, period, spotting, and any symptoms. Basic panel: TSH, prolactin, FSH, LH, estradiol, AMH (usually day 3–5 of cycle), transvaginal ultrasound. With that data, most questions resolve in a single visit.