Irregular Periods: Causes and When to See a Doctor
What "irregular" actually means
Cycles typically run 24–38 days. Variation of more than 7–9 days between consecutive cycles, missed cycles outside of pregnancy or breastfeeding, or cycles consistently shorter than 21 days are considered irregular by international gynecology guidelines (FIGO 2018). One off-cycle is rarely meaningful; a pattern over 3+ cycles is.
Common causes
Polycystic Ovary Syndrome (PCOS)
The most common cause of chronic irregularity in reproductive-age women. Driven by insulin resistance and hyperandrogenism. Often presents with acne, hirsutism, weight changes alongside cycle irregularity. Try our PCOS symptom checker.
Thyroid dysfunction
Both hypothyroidism and hyperthyroidism can disrupt the HPO axis. TSH is the standard screening test. Often resolves with treatment.
Stress and weight changes
Significant weight loss, very low calorie intake, intense training, or chronic stress can suppress GnRH pulsatility, causing hypothalamic amenorrhea. Cycles return when intake and training balance.
Perimenopause
Often starts in the early 40s but can begin in the late 30s. Cycle length variability increases, then cycles lengthen, then become anovulatory before stopping.
Hormonal contraception transitions
It is common to take 3–6 cycles for ovulation to fully resume after stopping hormonal birth control.
Structural causes
Fibroids, polyps, or adenomyosis usually present with heavy or prolonged bleeding rather than skipped periods.
Less common
Hyperprolactinemia, premature ovarian insufficiency, Cushing's, late-onset congenital adrenal hyperplasia. Your clinician will screen if signs point that way.
What evaluation typically looks like
- 3-cycle log (length, flow, symptoms)
- Pregnancy test (always first)
- Blood work: TSH, prolactin, FSH/LH/estradiol (timing matters), total/free testosterone, DHEA-S, fasting glucose/insulin, lipid panel
- Pelvic ultrasound
- Additional tests if specific causes suspected
What you can do today
- Start logging. Three full cycles of data is concrete enough to act on.
- Address foundations: sleep 7–9h, adequate calorie and protein intake, manage stress, moderate alcohol.
- If you fit a likely cluster (PCOS pattern, perimenopause age, thyroid signs), specifically test for it.
Frequently Asked Questions
How long should I wait before seeing a doctor?
If you have 3 consecutive irregular cycles, or any time you have missed periods for > 3 months outside of expected reasons, get evaluated.
Will going on the pill "fix" irregularity?
It will mask the symptom by overriding your natural cycle. Useful in some cases but not a diagnosis or root cause solution.
Can stress alone cause missed periods?
Yes — hypothalamic amenorrhea from significant chronic stress is common, especially when paired with low calorie intake or intense training.