# Thyroid and the Menstrual Cycle

URL: https://thethyroidologist.com/blog/thyroid-and-menstrual-cycle/
Published: 2025-11-10
Author: The Thyroidologist Editorial Team
Medical reviewer: Thyroid Specialist

> How thyroid disease affects periods, fertility and menopause — and what to expect when thyroid function is treated.

Thyroid hormone influences the hormones that control the menstrual cycle. When thyroid function is abnormal, periods can become heavier, lighter, irregular or absent — and fertility can be affected.

## How the thyroid affects periods

The thyroid interacts with the hypothalamus, pituitary and ovaries. It influences sex hormone binding globulin, prolactin and the balance of oestrogen and progesterone.

- **Hypothyroidism** often causes heavy, prolonged or irregular periods, and can contribute to infertility and miscarriage.
- **Hyperthyroidism** often causes lighter, shorter or absent periods.

## Heavy periods

Heavy menstrual bleeding is a common feature of hypothyroidism. It can also cause iron-deficiency anaemia, which adds fatigue. Treating the thyroid often improves flow over a few cycles.

Heavy bleeding has many other causes — fibroids, polyps, adenomyosis, bleeding disorders — so persistent symptoms need gynaecological assessment.

## Irregular or absent periods

Both thyroid extremes can disrupt ovulation, leading to irregular cycles or missed periods. In hyperthyroidism, periods may become very light or stop.

## Fertility

Thyroid dysfunction can affect ovulation and early pregnancy. Guidelines recommend optimising thyroid function before conception, especially in people with known thyroid disease.

If you are trying to conceive and have irregular periods, fatigue, weight change or a family history of thyroid disease, thyroid testing is reasonable.

## Pregnancy

Thyroid requirements increase in pregnancy, and untreated thyroid disease can affect both mother and baby. Monitoring is more frequent, and doses are adjusted.

## Menopause

Menopause and thyroid disease can overlap in symptoms — fatigue, sleep disturbance, mood changes and weight gain. Thyroid testing helps distinguish them. Hypothyroidism can also worsen menopausal symptoms.

## What to do

- Track your cycle and symptoms.
- Ask for thyroid testing if periods change alongside other thyroid symptoms.
- Correct thyroid function before trying to conceive if possible.
- Treat iron deficiency if present.
- Seek gynaecological assessment for persistent heavy or irregular bleeding.

## The bottom line

Thyroid disease is a treatable contributor to menstrual and fertility problems. If your cycle has changed alongside fatigue, weight change or temperature intolerance, a simple thyroid test is a reasonable first step.

## References & further reading

- [Periods — NHS](https://www.nhs.uk/conditions/periods/)
- [Thyroid disease and pregnancy — American Thyroid Association](https://www.thyroid.org/thyroid-disease-pregnancy/)

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