Thyroid conditions and your cycle

Too little or too much thyroid hormone can make your periods lighter, heavier or less regular. Periods can also stop. The pattern alone cannot tell you the cause. A clinician needs to consider your other symptoms and arrange tests.

The thyroid can change more than your cycle

The thyroid is a small gland in your neck. An underactive thyroid, called hypothyroidism, does not make enough thyroid hormone. An overactive thyroid, called hyperthyroidism, makes more than the body needs. Thyroid hormones affect how the body uses energy and how fast the heart beats.

With an underactive thyroid, you may feel very tired or colder than usual, have constipation or notice dry skin and hair changes. You may also have irregular or heavy periods. Symptoms often develop slowly. These symptoms can have other causes, which a clinician can help you explore.

An overactive thyroid can cause a fast or irregular heartbeat, feeling hot, trembling, anxiety or difficulty sleeping. Periods may become fewer or lighter. Mention symptoms outside your cycle too, even if they seem unrelated to the reason you booked the appointment.

What a thyroid check involves

A GP may ask about your symptoms, family history and any recent pregnancy, and examine your neck. Blood tests can measure thyroid-stimulating hormone, usually called TSH, and thyroid hormone. Sometimes further tests or a specialist referral are needed. Ask which tests are being requested and how you will receive the results.

Treatment depends on the condition. An underactive thyroid is usually treated with levothyroxine, which replaces missing thyroid hormone. Treatments for an overactive thyroid include medicines that reduce hormone production, radioiodine treatment or surgery. A specialist can discuss the benefits and drawbacks; your doctor or pharmacist can advise about your prescribed medicine.

Fertility and planning a pregnancy

Thyroid disease can affect ovulation and make pregnancy harder to achieve. If you want to become pregnant, tell your clinician when you discuss treatment. You can also ask how to manage the thyroid condition if pregnancy is not part of your plans.

Tell your GP or thyroid team if you are planning pregnancy. Contact them as soon as you find out you are pregnant if you already take thyroid medicine. Pregnancy can change treatment needs, so further blood tests and a review of your prescription may be needed. Do not stop or change a prescribed medicine without talking to your doctor.

Thyroid hormones support a baby’s brain development. Untreated thyroid conditions can cause pregnancy complications, but thyroid disease does not rule out a healthy pregnancy. Regular checks and the treatment prescribed by your clinician are part of managing it. Tell the maternity team about your thyroid history, including previous treatment.

Symptoms after a birth deserve a check too

Postpartum thyroiditis means inflammation of the thyroid after giving birth. It can cause an overactive phase followed by an underactive phase, although some people experience only one phase. In some people the underactive thyroid persists and needs ongoing treatment.

Tiredness, feeling hot, trouble sleeping or a fast heartbeat may occur during the overactive phase. Feeling cold, difficulty concentrating and dry skin may occur during the underactive phase. These symptoms can be mistaken for the tiredness and mood changes after a birth. Tell your doctor what has changed so they can check the cause.

Treatment after a birth depends on which phase you are in and how symptoms affect you. Some people need no medicine during the overactive phase; a clinician may offer treatment for troublesome symptoms. An underactive phase may need thyroid hormone replacement. Ask when thyroid function will be checked again and whether ongoing treatment is expected.

When to get help

Call 999 now (UK) or 911 (US), or your local emergency number, if a racing or irregular heartbeat comes with chest pain, breathlessness or feeling faint or fainting, or if a rapid heartbeat comes with a high temperature and severe agitation or confusion. Call immediately if someone loses consciousness.

Book a GP appointment in the UK, or see your doctor in the US or elsewhere, for persistent symptoms or period changes. For a new pregnancy while taking thyroid medicine, contact your treating team today. Bring your medicine list and a short note of what has changed; ask who will coordinate thyroid care with your maternity care.