Irregular Periods — Causes and Treatment
Current Guidance Update
Normal Menstrual Cycle
A normal menstrual cycle ranges from 21–35 days. Cycles that consistently fall outside this range should be medically evaluated.
Thyroid Function Testing
All women presenting with menstrual irregularity should undergo thyroid function testing to identify or exclude underlying thyroid disorders.
Common Cause of Oligomenorrhoea
PCOS is recognized as the most common cause of oligomenorrhoea in women of reproductive age and should be considered during clinical assessment.
Early Assessment
Persistent irregular or absent periods should be assessed promptly to identify hormonal, metabolic, or reproductive conditions and initiate appropriate management.
Introduction
Irregular Periods: Causes, Investigation & Treatment
Defining Irregular Periods
A normal menstrual cycle lasts 21–35 days with bleeding for 2–7 days. Oligomenorrhoea refers to cycles over 35 days, polymenorrhoea to cycles under 21 days, amenorrhoea to absence of periods for more than 3 months, and metrorrhagia to irregular bleeding between periods.
Common Causes
- PCOS – most common cause of oligomenorrhoea
- Hypothalamic amenorrhoea
- Thyroid dysfunction
- Hyperprolactinaemia
- Premature ovarian insufficiency (POI)
- Anatomical abnormalities
- Medication or contraception related
- Perimenopause
Recommended Investigation
- Pregnancy test as the first investigation
- FSH, LH, oestradiol, prolactin, AMH
- TSH and free T4 assessment
- Androgen profile
- Pelvic ultrasound examination
Treatment by Cause
- PCOS – lifestyle changes and hormonal therapy
- Hypothalamic amenorrhoea – weight restoration & stress management
- Thyroid disorders – hormone replacement or medical treatment
- Hyperprolactinaemia – dopamine agonists
- POI – hormone replacement therapy
- Perimenopause – HRT discussion and symptom support
Frequently Asked Questions
Is it harmful to have irregular periods?
Anovulatory cycles are associated with unopposed oestrogen stimulation of the endometrium, increasing endometrial hyperplasia risk over time — evaluation and management matters beyond the symptom itself.
My periods became irregular after stopping the pill — is this normal?
Post-pill amenorrhoea for up to 3–6 months is common and usually benign. Persistence beyond 6 months warrants investigation.
Conclusion
Irregular periods deserve clinical investigation, not reassurance without assessment. Identifying the underlying cause allows targeted management that restores menstrual health and supports fertility goals.
Sources & References
This article draws on guidance current at the time of writing from the following bodies and publications:
- ACOG (2023)
- RCOG (2024)
- NICE CG44 (updated 2023)
General reference bodies for women's health guidance:
RCOG
rcog.org.ukACOG
acog.orgFIGO
figo.orgWHO
who.intNICE
nice.org.uk⚠ IMPORTANT DISCLAIMER
This article is provided for general knowledge and reference purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. No medication, treatment, or change to your healthcare should be undertaken based on this content without first consulting a qualified doctor. Always seek the advice of your physician or another qualified health provider with any questions you may have regarding a medical condition.
