Irregular Menstruation
Menstrual irregularities — heavy, prolonged, missed or unpredictable periods — have many causes including PCOS, stress, perimenopause, and thyroid dysfunction.
Thyroid disorders are a recognised contributor, particularly in women with other symptoms.
Last medically reviewed: 1 November 2025
How thyroid affects cycles
Hypothyroidism commonly causes heavier, longer or more frequent periods; hyperthyroidism tends to cause lighter, less frequent periods or missed cycles. Severe dysfunction of either type can disrupt ovulation.
Thyroid dysfunction in pregnancy increases risks — preconception thyroid testing is recommended for women with irregular cycles or thyroid history.
Other common causes
PCOS is the most common cause of irregular periods in reproductive-age women. Perimenopause, stress, significant weight change, excessive exercise, and medications (antipsychotics, chemotherapy) also disrupt cycles.
Structural problems — fibroids, polyps — can cause heavy bleeding specifically.
When to evaluate thyroid
Thyroid testing is reasonable when irregular periods accompany hypothyroid or hyperthyroid symptoms — fatigue, weight change, temperature intolerance, mood changes — or when fertility is a concern.
Persistent irregular cycles warrant evaluation regardless of thyroid status — PCOS and other causes are common.
Frequently asked questions
Can thyroid problems affect fertility?
Yes — both hypo- and hyperthyroidism can disrupt ovulation and increase miscarriage risk. Thyroid testing is standard in fertility workups.
Will treating thyroid normalise my periods?
Often yes — cycles typically improve as thyroid function normalises, though other causes may need separate treatment.
Should I test thyroid before pregnancy?
If you have thyroid disease or risk factors, preconception testing is recommended — optimal thyroid function in early pregnancy protects fetal development.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
Ready to discuss your thyroid health?
Book a specialist consultation — in person or by teleconsultation.