Thyroid Test: What It Means for Fertility
Thyroid hormones play a vital role in regulating your cycle, ovulation, and overall reproductive health. A simple thyroid test can reveal whether your thyroid is supporting — or disrupting — your fertility. Here’s all you need to know, every step of the way.
Author
Tassia O’Callaghan
Reviewed by
Kayleigh Hartigan
16 min read
Published 24 October 2025
Spotlight:
- A thyroid test is usually a simple blood test that checks if your thyroid is underactive (hypothyroidism) or overactive (hyperthyroidism).
- Thyroid hormones play a key role in regulating your cycle, ovulation, implantation, and early pregnancy.
- Many fertility clinics include thyroid testing as part of an initial Fertility MOT — especially if you’re TTC, have irregular cycles, or have a history of miscarriage.
- Common tests include TSH, free T4, free T3, and thyroid antibodies (to check for autoimmune thyroid conditions such as Hashimoto’s or Graves’ disease).
- Thyroid imbalance is treatable, and managing it can improve both fertility outcomes and pregnancy health.
What is a thyroid test?
A thyroid test is usually a simple blood test that checks how well your thyroid gland is working. The thyroid itself is a small, butterfly-shaped gland at the base of your neck. Despite its size, it plays a big role in regulating metabolism, growth, energy balance, and even your heart function. Because these hormones affect so many systems in the body, thyroid health can directly influence your cycle and your chances of conceiving. [1,2]
The first-line test is typically TSH (thyroid-stimulating hormone). This is made in the pituitary gland in your brain, which acts like a “messenger,” telling the thyroid how much hormone to release. A TSH test is often the starting point for checking whether your thyroid is underactive (hypothyroidism) or overactive (hyperthyroidism). [3]
Beyond TSH, a full thyroid profile may include:
- Free T4 (thyroxine): The main hormone produced by the thyroid. Measuring “free” T4 (the part not bound to proteins in your blood) gives a clearer picture of what’s actually available for your body to use. [4]
- Free T3 (triiodothyronine): The active form of thyroid hormone that drives how your cells use energy.
Sometimes T4 levels can look normal while T3 is raised, so both are checked if hyperthyroidism is suspected. [5] - Thyroid antibodies: Proteins made by your immune system that can mistakenly attack the thyroid. These tests help identify autoimmune thyroid conditions such as Hashimoto’s disease (a common cause of hypothyroidism) or Graves’ disease (the most common cause of hyperthyroidism). [6]
Fertility Test: What It Is, What It Costs, and What It Tells You
Whether you’re trying to conceive or simply want to understand more about your reproductive health, a fertility test can help shed light on what’s happening in your body — and what your next steps might be.
Who are thyroid tests for?
Thyroid testing can be a useful part of fertility investigations, depending on your medical history and symptoms. While some hospital guidance suggests delaying thyroid tests during or soon after an acute, non-thyroid illness (because results can be misleading), fertility pathways often do suggest TFTs (thyroid function tests) early — especially at referral — to avoid missing a modifiable cause of subfertility or miscarriage. Both can be true: timing matters, and so does not overlooking a common, fixable issue. [7,8,9]
You might consider a thyroid test if you’re:
- Trying to conceive (TTC) and your cycles are irregular, absent, unusually heavy/light, or have recently changed.
- Experiencing recurrent miscarriage or early pregnancy losses.
- Starting or planning fertility treatment (e.g., IVF, ICSI, IUI, egg freezing) — many clinics include TFTs in the pre-treatment workup.
- Pregnancy-planning after a past thyroid condition (e.g., Graves’ or Hashimoto’s) — even if you feel well now, antibodies can persist and are important to know about before and during pregnancy.
- Postpartum (within 12 months of birth) — especially if you have thyroid antibodies or had postpartum thyroiditis previously; thyroid changes are common after delivery and can affect future TTC plans.
- Noticing symptoms that commonly overlap with thyroid issues: unexplained weight change, fatigue, feeling unusually cold or hot, anxiety/low mood, palpitations, hair thinning, dry skin, or new period changes.
- Over 35 and TTC — thyroid issues become more common with age and can influence ovulation and implantation.
- Managing autoimmune conditions (you or close relatives), as these can cluster with autoimmune thyroid disease.
- Taking medicines that affect thyroid function (current or recent), such as amiodarone or lithium; your clinician may recommend regular TFTs.
- Male partners with fertility concerns — hyperthyroidism can reduce sperm counts; checking thyroid function can be part of a thorough work-up.
A quick note on when to test
- If you’ve had a recent acute illness (flu, COVID-19, hospitalisation), book thyroid bloods after recovery. Non-thyroidal illness can temporarily skew results; many labs advise waiting up to three months post-illness unless your clinician suspects true thyroid disease now.
- If you’re already on thyroid medication, your clinician may time bloods in relation to your dose and adjust monitoring frequency when TTC or pregnant.
- If you take supplements that can interfere with assays (such as high-dose biotin), you’ll usually be asked to pause them for a short window before your test. Your clinician or lab form will spell out the details.
How is thyroid tested?
There are several ways to check thyroid function, depending on whether your clinician is looking for a hormone imbalance, autoimmune activity, or structural changes in the gland. [1,8]
- Blood tests (first line): This is the most likely form of thyroid testing you’ll encounter. A small blood sample from your arm, usually testing TSH, free T4, and sometimes free T3. Thyroid antibody tests may also be added to check for autoimmune conditions. Many labs use a reflex approach, adding extra tests automatically if TSH is out of range.
- At-home blood tests: Finger-prick kits that you send to a lab. These can give a useful first look, but abnormal results should always be confirmed with a venous blood test.
There are other methods to test thyroid function, but these are typically only used if something is found in a blood test:
- Ultrasound: A painless scan using sound waves to check the thyroid’s size, shape, and texture. Often recommended if you have a swelling in your neck or suspected thyroid nodule.
- Thyroid scan (scintigraphy): A test using a small amount of radioactive iodine to see how the thyroid is working and whether nodules are active. Not suitable if you are pregnant or breastfeeding.
- Radioactive iodine uptake (RAIU) test: Measures how much iodine the thyroid absorbs over several hours. Helps clarify the cause of hyperthyroidism.
- Fine-needle aspiration (FNA) biopsy: A quick outpatient procedure where a thin needle removes a small tissue sample from a thyroid nodule, usually guided by ultrasound, to check if it’s benign or requires further treatment.
Find the right clinic for you
Choosing a clinic is one of the biggest decisions you’ll make. We’ll find the best options for you and arrange your pre-treatment tests, empowering you from this point onwards.
Why do I need to do a thyroid test?
Checking your levels early in a Fertility MOT gives you and your clinician a clear baseline, helps explain symptoms like cycle changes or fatigue, and highlights any autoimmune flags that might shape monitoring in pregnancy. In short: it’s a fast way to rule out a common, manageable barrier to conceiving. [7,8,10]
More specifically, clinics often include TFTs early in a fertility work-up because thyroid imbalance can influence:
- Ovulation and cycle regularity: Thyroid hormones help regulate the brain–ovary signalling that triggers ovulation. Imbalance can lead to irregular, light, heavy, or absent periods and make timing sex or treatment harder.
- Conception chances and implantation: Suboptimal thyroid status may alter endometrial receptivity and luteal function, making it harder for an embryo to implant and develop.
- Early pregnancy loss: Untreated thyroid dysfunction is linked to a higher risk of miscarriage; checking and optimising levels before conception helps lower that risk.
- Pregnancy health: Active thyroid disease can be associated with blood pressure issues, foetal growth concerns, and preterm birth. Knowing your baseline allows your team to monitor and manage safely.
- Autoimmune risk: If you’ve ever had Graves’ or Hashimoto’s, antibody testing can flag whether monitoring is needed in pregnancy (some antibodies can cross the placenta). This is about planning, not alarm.
- Male fertility: In men, hyperthyroidism can temporarily lower sperm count and impair motility. Testing is a pragmatic part of a complete couple’s assessment.
- After pregnancy and between pregnancies: Postpartum thyroiditis is common and can recur. If you’ve had it before, a check before trying again (and early in the next pregnancy) helps keep you on track.
There are also some potential high or low thyroid symptoms you might be experiencing, which could mean it’s worth getting a full thyroid test: [11,12,13]
Weight
Weight gain, often stubborn despite diet or exercise; fluid retention can add to the feeling of heaviness.
Unexplained weight loss despite normal or increased appetite; harder to maintain muscle and healthy body mass.
Energy and sleep
Persistent fatigue, sluggishness, tendency to feel unusually cold, “slow” metabolism. Sleep may not feel restorative.
Restlessness, heat intolerance, difficulty staying still; insomnia, racing heart, or night sweats may keep you awake.
Mood and cognition
Low mood, brain fog, forgetfulness, difficulty concentrating; depression is more common.
Anxiety, nervous energy, irritability, mood swings; some people feel constantly “wired” or jittery.
Cycle and periods
Heavy, prolonged, or irregular bleeding; sometimes periods stop altogether (amenorrhoea). Can lead to anaemia.
Lighter or absent periods; sometimes shorter cycles. May also affect ovulation timing.
Hair, skin, and nails
Dry or itchy skin, hair thinning (especially outer eyebrows), brittle nails, hoarse or croaky voice.
Fine, thinning hair; fragile or sweaty skin; loose nails; itching or hives.
Fertility
Can disrupt ovulation, affect egg quality, and increase miscarriage risk if untreated.
Can disrupt ovulation, reduce implantation chances, and increase risks in pregnancy (miscarriage, preterm birth, high blood pressure).
Can I ask my GP for a thyroid test?
Yes. If you’re experiencing symptoms or have risk factors, your GP can arrange thyroid testing. In practice, not everyone is automatically offered a test — some areas apply strict criteria, which can mean longer waits or limited access unless your case is clearly identified. [11,12]
If you’d like quicker answers or a more detailed hormone profile, you don’t have to rely on the NHS alone. Many private fertility clinics include thyroid checks as part of their initial assessment, and at-home kits can also provide a snapshot of your thyroid health, with results sent to a lab for analysis. Any abnormal findings can then be followed up in a clinic setting.
This means you have more than one route to getting clarity, whether you’re beginning fertility treatment or simply want reassurance that your thyroid isn’t standing in the way of conceiving.
Your NHS Eligibility
Use our NHS IVF Eligibility Calculator to discover if you can access free IVF and IUI.
How much does a thyroid test cost?
The cost of thyroid testing can vary depending on where and how you choose to have it done. Some people may be eligible for free testing through the NHS, while others prefer to book privately for faster results or a more detailed hormone profile.
- NHS thyroid test: Free — available when your GP or specialist recommends testing based on your symptoms or medical history.
- Private basic thyroid test: ~£55–£85 — usually measures key hormones like TSH, T3, and T4.
- Private full thyroid profile test: ~£85–£200 — offers a more detailed look at thyroid function, often including antibodies that can help identify autoimmune thyroid conditions.
- At-home thyroid test kits: ~£20–£50 — a convenient option if you prefer to test from home, though results may need follow-up with your GP or fertility specialist.
Can I test my thyroid myself?
Yes — there are at-home thyroid test kits available, usually as finger-prick blood tests you post to a lab. They can be a convenient first step if you’re curious about your thyroid status or want a quick check while TTC. Some kits measure TSH only, while others include free T4, free T3, and sometimes thyroid antibodies.
It’s worth remembering that these tests are a screening tool, not a diagnosis. There are a lot of factors that can affect the results. And because thyroid hormones play such a central role in fertility and pregnancy, the numbers often need interpreting in context — not just against the “normal” population ranges.
That’s why we always recommend reviewing your results with a healthcare professional. They’ll be able to confirm the findings, explain what they mean for your fertility journey, and advise on whether any treatment or monitoring is needed.
Understanding your thyroid test results
When you get your thyroid results back, it can feel overwhelming — especially when numbers don’t always match how you feel. Thyroid hormones don’t exist in isolation: they’re part of a feedback loop between your brain (the pituitary gland) and your thyroid gland, and levels can vary depending on age, pregnancy, illness, or even the lab method used.
For fertility specifically, many specialists prefer your results to sit in a tighter “optimal” window than what’s considered normal for the general population. This is because small shifts in thyroid function — even within the wider “normal” range — can impact ovulation, implantation, or early pregnancy.
Here’s a simple thyroid test results chart to help you understand the reference ranges you’re likely to see on a lab report, and how they compare with fertility-focused targets: [14,15,16]
Hormone
Normal range (general population)
Fertility/TTC optimal range
High range (general population)
Low range (general population)
TSH (mIU/L)
0.27 – 4.2
1.0 – 2.5 (when TTC or in early pregnancy)
> 4.2 (suggests underactive thyroid)
< 0.27 (suggests overactive thyroid)
Free T4 (pmol/L)
12.0 – 22.0
Mid–upper range often preferred
> 22.0
< 12.0
Free T3 (pmol/L)
3.1 – 6.8
Mid-range often preferred
> 6.8
< 3.1
Thyroid antibodies (Anti-TPO, IU/ml)
< 25 = negative 25–35 = borderline
Ideally negative when TTC or pregnant
> 35 (suggests autoimmune thyroid disease)
N/A (antibodies are either present or absent)
Next steps after a thyroid test
Getting thyroid blood work back is only the beginning. What happens next depends on whether your results fall in the “normal” range, sit in a borderline area, or show clear signs of under- or overactivity.
- Normal results: If your levels are within range, your GP or fertility team may rule out thyroid imbalance as a direct cause of fertility issues. That said, some clinics prefer to keep TSH on the lower end of normal (under 2.5 mIU/L) before and during pregnancy, so your doctor may still suggest closer monitoring if you’re trying to conceive. [8]
- Borderline or abnormal results: If your results hint at underactive thyroid (hypothyroidism) or overactive thyroid (hyperthyroidism), you’ll usually be referred for follow-up tests or treatment. For hypothyroidism, this often means levothyroxine to restore hormone balance. For hyperthyroidism, anti-thyroid medication may be prescribed while further investigations confirm the underlying cause (such as Graves’ disease or thyroiditis). [17,18]
- Follow-up: Thyroid hormones don’t stand still — they can shift with pregnancy, medication changes, or even recovery from illness. That’s why regular blood tests may be standard for some clinics or GPs after an initial diagnosis. If you’re TTC or pregnant, your team will usually want to keep a closer eye on your thyroid, adjusting medication as needed to support both your health and the pregnancy. [8]
How quickly can thyroid levels change?
Thyroid levels can shift within weeks, which is why blood tests are usually repeated about 6–8 weeks after starting or adjusting medication. Regular monitoring matters: staying too low can affect energy, cycles, and pregnancy outcomes, while pushing levels too high can impact bone and heart health. [19]
Most antibodies don’t need retesting, but TSH receptor antibodies in Graves’ disease may be checked to guide treatment decisions. In short: levels don’t change overnight, but they do respond over time — and staying on track means follow-up tests and personalised targets with your clinician.
Is it worth getting your thyroid checked?
If fertility is on your mind, yes — thyroid testing is a small step with big upside. Thyroid hormones help coordinate ovulation, implantation, and early pregnancy; even mild imbalance can nudge cycles off-track or raise miscarriage risk. A quick blood test can rule in (or rule out) a common, fixable factor so you and your clinician can focus effort where it counts.
You don’t need blanket screening forever, but it’s especially worthwhile if you’re TTC with irregular cycles, experiencing recurrent loss, starting IVF or egg freezing, have a personal/family history of thyroid or autoimmune disease, are postpartum, or you’re over 35. For most people, getting checked provides clarity and, when needed, straightforward treatments that support both fertility and pregnancy.
You can start with your GP, a fertility clinic, or an accredited at-home kit (then confirm results in clinic). And because numbers need context, we always recommend going over your results with a healthcare professional so you get tailored guidance on what — if anything — to do next.
Thyroid test FAQs
What are early warning signs of thyroid problems?
Early warning signs of thyroid problems can be subtle and easy to miss.
With an underactive thyroid (hypothyroidism), you might notice unexplained fatigue, weight gain, feeling unusually cold, heavy or irregular periods, or changes to your skin and hair. [11]
With an overactive thyroid (hyperthyroidism), early signs often include anxiety, restlessness, heat intolerance, trouble sleeping, or unexplained weight loss despite eating normally. Some people also spot changes in their heartbeat, mood, or energy levels. [12]
If you notice a cluster of these symptoms, it’s worth asking your GP for a thyroid test to rule it in or out.
What’s the best time of day to test thyroid?
It depends on who’s carrying out your test — it’s best to follow their guidance. But if you’re doing a thyroid test at home, it can be beneficial to aim for an early-morning blood draw (around 8–9am), ideally before breakfast (and before your levothyroxine dose if you take one). TSH follows a daily rhythm and can fall later in the morning or after eating, so testing at the same time and under the same conditions each visit gives the most comparable results. [20,21]
How many times a year should you get your thyroid checked?
The British Thyroid Foundation recommends that most people need their levels checked once a year, although your doctor may recommend testing more often if you’re trying to conceive, pregnant, adjusting medication, or have a history of thyroid treatment. If you don’t have a diagnosis but fall into a higher-risk group (such as recurrent miscarriage, fertility problems, or certain autoimmune conditions), your GP may suggest regular checks too. [22]
Are thyroid conditions hereditary?
Yes — thyroid conditions often run in families, especially the autoimmune types like Hashimoto’s and Graves’.
Research suggests our thyroid “set point” is partly genetic (a substantial share of TSH and thyroid hormone levels is inherited), and specific genes involved in immune regulation and the thyroid itself can raise susceptibility. That said, genes aren’t destiny: they increase risk rather than guarantee a condition, and environmental factors and life stages (e.g., pregnancy, postpartum) also play a role. [11,12,23]
If thyroid disease is common in your family — and you’re trying to conceive or have pregnancy plans — it’s sensible to ask your GP about a thyroid check so you can plan care proactively.
What is the most common thyroid problem?
The most common thyroid problem is hypothyroidism (an underactive thyroid), most often caused by autoimmune Hashimoto’s disease. It affects around 2% of people in the UK overall and more than 5% of those over 60, with women affected far more often than men. By contrast, the most common cause of an overactive thyroid is Graves’ disease, but hyperthyroidism is less common overall. If fertility is your focus, both conditions are manageable — and treating them can help protect ovulation, pregnancy health and long-term wellbeing. [11,12,17,24]
Sources
- National Institute of Diabetes and Digestive and Kidney Diseases. Thyroid Tests. Last Reviewed May 2017.
- British Thyroid Foundation. Your thyroid gland.
- Pirahanchi Y, Toro F, Jialal I. Physiology, Thyroid Stimulating Hormone. Updated 2023 May 1.
- NHS, The Newcastle Upon Tyne Hospitals, NHS Foundation Trust. Free T4, serum. Page last updated: 24/12/2024.
- NHS, South Tees Hospitals, NHS Foundation Trust. Free Triiodothyronine (FT3). Page last updated: 27/04/2022.
- British Thyroid Foundation. Thyroid antibodies explained.
- British Thyroid Foundation. Pregnancy and fertility in thyroid disorders.
- NHS Grampian. Fertility Clinic – Thyroid Testing. Last Review – 02 July 2019.
- National Institute for Health and Care Excellence. How should I assess a person with suspected hypothyroidism? Last revised in November 2024.
- UK Guidelines for the Use of Thyroid Function Tests (July 2006).
- NHS. Underactive thyroid (hypothyroidism). Page last reviewed: 28 April 2025.
- NHS. Diagnosis-Overactive thyroid (hyperthyroidism). Page last reviewed: 11 April 2023.
- Addanki S, Patel K, Patel L, Smith B, Patel P, Uppalapati S, Nathanson L. Thyroid Function and Sleep Patterns: A Systematic Review. Cureus. 2024 Jun 29;16(6):e63447. doi: 10.7759/cureus.63447. PMID: 39077291; PMCID: PMC11285688.
- NHS, Gloucestershire Hospitals, NHS Foundation Trust. Thyroid Function Tests (TSH, FT4, FT3). Page Last Updated: 10/11/22.
- NHS, North Bristol, NHS Trust. Thyroid Function Tests.
- NHS, Gloucestershire Hospitals, NHS Foundation Trust. Thyroid Antibodies (TPO).
- National Institute for Health and Care Excellence. Thyroid disease: assessment and management.
- Chaplin, S., 2020. Summary of NICE guidance on thyroid disease. Prescriber, 31(5), pp.20-22.
- British Thyroid Foundation. Thyroid function tests.
- Mahadevan S, Sadacharan D, Kannan S, Suryanarayanan A. Does Time of Sampling or Food Intake Alter Thyroid Function Test? Indian J Endocrinol Metab. 2017 May-Jun;21(3):369-372. doi: 10.4103/ijem.IJEM_15_17. PMID: 28553588; PMCID: PMC5434716.
- Mirjanic-Azaric, B., Stojakovic-Jelisavac, T., Vukovic, B., Stojanovic, D., Vujnic, M. and Uletilovic, S., 2015. The impact of time of sample collection on the measurement of thyroid stimulating hormone values in the serum. Clinical Biochemistry, 48(18), pp.1347-1349.
- British Thyroid Foundation. Thyroid function testing.
- Panicker V. Genetics of thyroid function and disease. Clin Biochem Rev. 2011 Nov;32(4):165-75. PMID: 22147956; PMCID: PMC3219766.
- British Thyroid Foundation. A guide to commonly used thyroid terms.