--- title: "Thyroid conditions and your cycle" description: "How thyroid conditions can affect periods, fertility and pregnancy, and why symptoms after giving birth are worth checking." url: "https://myruva.co/learn/thyroid-and-your-cycle" language: "en-GB" topic: "Hormones" published: "2026-10-18" updated: "2026-10-19" author: "Ruva team" reading_minutes: 4 --- # Thyroid conditions and your cycle How thyroid conditions can affect periods, fertility and pregnancy, and why symptoms after giving birth are worth checking. *Written and reviewed by the Ruva team · Updated 2026-10-19 · Hormones* ## Key points - Too much or too little thyroid hormone can change your periods. - Blood tests help a clinician check how your thyroid is working. - Your thyroid treatment needs checking when you plan a pregnancy or get pregnant. - The thyroid can become inflamed after giving birth. Too little or too much thyroid hormone can make your periods lighter, heavier or less regular. Periods can also stop. The pattern alone can’t tell you the cause. A clinician needs to look at 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 (hypothyroidism) doesn’t make enough thyroid hormone. An overactive thyroid (hyperthyroidism) makes more than the body needs. Thyroid hormones affect how your body uses energy and how fast your heart beats. With an underactive thyroid, you may feel very tired or colder than usual. You may have constipation, dry skin or changes to your hair. You may also have irregular or heavy periods. Symptoms often come on slowly. They can have other causes too, and a clinician can help you find out. An overactive thyroid can cause a fast or irregular heartbeat, feeling hot, shaking, anxiety or trouble sleeping. Periods may come less often or get lighter. Mention symptoms that aren’t about your cycle too, even if they seem to have nothing to do with why you booked. ## What a thyroid check involves A GP may ask about your symptoms, family history and any recent pregnancy, and feel your neck. Blood tests can measure thyroid-stimulating hormone (TSH) and thyroid hormone. Sometimes you need more tests or a referral to a specialist. Ask which tests you’re having and how you’ll get the results. Treatment depends on the condition. An underactive thyroid is usually treated with levothyroxine, which replaces the missing hormone. For an overactive thyroid, treatments include medicines that lower hormone production, radioiodine treatment or surgery. A specialist can talk through the pros and cons. Your doctor or pharmacist can advise about the medicine you’re prescribed. ## Fertility and planning a pregnancy Thyroid disease can affect ovulation and make it harder to get pregnant. If you want to get pregnant, tell your clinician when you talk about treatment. You can also ask how to manage your thyroid if pregnancy isn’t part of your plans. Tell your GP or thyroid team if you’re planning a pregnancy. If you already take thyroid medicine, contact them as soon as you find out you’re pregnant. Pregnancy can change how much treatment you need, so you may need more blood tests and a change to your prescription. Don’t stop or change a prescribed medicine without talking to your doctor. Thyroid hormones help a baby’s brain develop. Untreated thyroid problems can cause problems in pregnancy, but thyroid disease doesn’t rule out a healthy pregnancy. Regular checks and the treatment your clinician prescribes are part of managing it. Tell the maternity team about your thyroid history, including any past treatment. ## Symptoms after a birth deserve a check too Postpartum thyroiditis means the thyroid becomes inflamed after giving birth. It can cause an overactive phase followed by an underactive phase, though some people only have one. For some people, the underactive thyroid lasts and needs ongoing treatment. In the overactive phase, you may feel tired or hot, have trouble sleeping or a fast heartbeat. In the underactive phase, you may feel cold, find it hard to concentrate and have dry skin. These symptoms can be mistaken for the tiredness and mood changes that come after a birth. Tell your doctor what has changed so they can check the cause. Treatment after a birth depends on which phase you’re in and how your symptoms affect you. Some people need no medicine during the overactive phase. A clinician may offer treatment if symptoms are bothering you. An underactive phase may need thyroid hormone replacement. Ask when your thyroid will be checked again and whether you’re likely to need ongoing treatment. ## 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. Do the same if a fast heartbeat comes with a high temperature and severe agitation or confusion. Call straight away if someone loses consciousness. Book a GP appointment in the UK, or see your doctor in the US or elsewhere, for symptoms that won’t go away or changes to your periods. If you’ve just found out you’re pregnant and take thyroid medicine, contact your treating team today. Bring your medicine list and a short note of what has changed. Ask who will join up your thyroid care with your maternity care. ## When to get help - **Emergency:** 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 fast heartbeat comes with a high temperature and severe agitation or confusion. Call straight away if someone loses consciousness. - **Same day:** Contact your GP or thyroid team today (UK), or your treating doctor (US or elsewhere), if you take thyroid medicine and have just found out you’re pregnant. - **Book an appointment:** Book a GP appointment (UK), or see your doctor (US or elsewhere), if changes to your periods come with tiredness that won’t go away, feeling unusually cold or hot, or changes in weight. ## Where you live Services and advice differ between countries. - **UK:** If you have an underactive thyroid and are pregnant or planning a pregnancy, the NHS advises telling your GP. You’ll need more tests and a review of your treatment. - **US:** If you take levothyroxine for an underactive thyroid, NIDDK advises contacting your doctor as soon as you know you’re pregnant. - **Elsewhere:** Elsewhere, ask your local doctor or maternity team to join up your thyroid checks and treatment during pregnancy. ## Sources 1. [Thyroid disease](https://womenshealth.gov/a-z-topics/thyroid-disease), Office on Women’s Health 2. [Underactive thyroid (hypothyroidism)](https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/), NHS 3. [Thyroid Disease & Pregnancy](https://www.niddk.nih.gov/health-information/endocrine-diseases/pregnancy-thyroid-disease), NIDDK 4. [Overview - Overactive thyroid (hyperthyroidism)](https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/), NHS 5. [Heart palpitations](https://www.nhs.uk/symptoms/heart-palpitations/), NHS 6. [Complications - Overactive thyroid (hyperthyroidism)](https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/complications/), NHS 7. [Thyroid storm](https://medlineplus.gov/ency/article/000400.htm), MedlinePlus --- This guide is general information to help you keep and use your own records. It isn’t medical advice. If you’re worried about a symptom, or something changes suddenly, talk to a doctor, nurse or pharmacist.