Understanding Hashimoto’s Thyroiditis, Fertility, Miscarriage & Pregnancy

A Consultant Guide to Optimising Thyroid Health Before, During and After Pregnancy

Introduction

Being diagnosed with Hashimoto’s thyroiditis can raise many questions, particularly if you are planning a pregnancy, experiencing fertility difficulties or have suffered one or more miscarriages.

Perhaps you have been told your thyroid blood tests are “normal” despite testing positive for thyroid antibodies. You may have read conflicting advice online about levothyroxine, selenium, iodine or dietary changes. Alternatively, you may already be taking thyroid medication and want to know whether your dose should change before or during pregnancy.

These are common concerns. Although Hashimoto’s thyroiditis is the most frequent cause of hypothyroidism in countries with adequate iodine intake, its effects on fertility and pregnancy are often misunderstood. Research continues to evolve, and recommendations have become increasingly nuanced. Not every woman with thyroid antibodies requires treatment, but equally, some women benefit from careful monitoring and optimisation before conception.

At Innermost Healthcare, we believe that management should be individualised. Rather than relying on a single blood test, we assess the wider clinical picture, including thyroid function, thyroid antibody status, symptoms, reproductive history, previous pregnancy outcomes and other factors that may influence fertility or miscarriage risk.

This guide brings together current evidence, national and international guidance, and our experience in consultant-led maternal medicine to explain what Hashimoto’s thyroiditis is, how it may affect fertility and pregnancy, and how women can be monitored and supported before, during and after pregnancy.

Thyroid Gland Anatomy and Hormones

The thyroid gland produces two principal hormones:

These hormones regulate almost every organ in the body, influencing:

When thyroid hormone production falls, the pituitary gland responds by increasing secretion of thyroid stimulating hormone (TSH) in an attempt to stimulate the thyroid.

What is Hashimoto’s Thyroiditis?

Simple thyroid illustration with immune cells attacking the thyroid gland.

Hashimoto’s thyroiditis is an autoimmune condition in which the body’s immune system mistakenly recognises components of the thyroid gland as foreign and produces antibodies against them. Over time, this chronic inflammatory process may gradually damage thyroid tissue and reduce its ability to produce thyroid hormones.

The condition was first described by the Japanese physician Dr Hakaru Hashimoto in 1912 and remains the commonest cause of hypothyroidism in the UK and many other developed countries.

Unlike infections, autoimmune conditions are not contagious. They arise because the immune system becomes dysregulatedand targets the body’s own tissues.

What are Anti-TPO Antibodies?

The hallmark of Hashimoto’s thyroiditis is the presence of antibodies directed against proteins within the thyroid gland.

The most important are:

Thyroid peroxidase is an enzyme essential for producing thyroid hormones. Anti-TPO antibodies target this enzyme and are found in the majority of individuals with Hashimoto’s thyroiditis.

Importantly, having anti-TPO antibodies does not necessarily mean that thyroid function is abnormal.

Many women have:

Conversely, others gradually develop hypothyroidism over months or years.

This distinction is particularly important when counselling women planning pregnancy because the presence of thyroid antibodies alone does not automatically mean treatment is required. Instead, thyroid function, symptoms and reproductive history all need to be considered together.

How Common is Hashimoto’s Thyroiditis?

Hashimoto’s thyroiditis is one of the commonest autoimmune conditions worldwide.

It is estimated that:

The condition is particularly common in women of reproductive age, making it highly relevant to fertility and pregnancy care.

Why Does Hashimoto’s Develop?

No single cause has been identified. Instead, Hashimoto’s thyroiditis appears to result from an interaction between genetic susceptibility and environmental triggers.

Factors associated with increased risk include:

Research continues into other possible contributors, including vitamin D status, selenium, viral infections and alterations in the gut microbiome, although evidence for many proposed factors remains incomplete.

Common Symptoms

One challenge with Hashimoto’s thyroiditis is that symptoms develop gradually and often overlap with those experienced during everyday life or pregnancy.

Women may report:

However, symptoms are not specific to Hashimoto’s thyroiditis, and many women with positive thyroid antibodies feel entirely well. Blood tests remain essential when assessing thyroid function.

How is Hashimoto’s Diagnosed?

Diagnosis usually combines clinical assessment with laboratory investigations.

Initial blood tests commonly include:

A thyroid ultrasound may also be useful, particularly if there is:

Ultrasound typically demonstrates a gland that appears diffusely heterogeneous with reduced echogenicity, reflecting chronic autoimmune inflammation. However, ultrasound findings alone are not diagnostic and should always be interpreted alongside clinical history and blood test results.

Why “Normal” Blood Tests Can Still Be Important

A common source of confusion is that many women with Hashimoto’s thyroiditis initially have normal thyroid hormone levels.

This occurs because the immune system may begin attacking the thyroid years before sufficient tissue damage has occurred to reduce hormone production.

Consequently, thyroid antibodies can be detected long before TSH or free T4 become abnormal.

For women planning pregnancy, this distinction is important. While thyroid function may currently be normal, pregnancy places increased demands on the thyroid gland, and some women develop hypothyroidism during pregnancy if thyroid reserve is limited.

Careful monitoring, rather than immediate treatment for everyone, is therefore often the most appropriate approach.

Why Hashimoto’s Matters in Pregnancy

Pregnancy produces profound hormonal and immunological changes.

During early pregnancy:

Untreated overt hypothyroidism is associated with increased risks including:

The management of women with normal thyroid function but positive anti-TPO antibodies is less straightforward. Although thyroid autoimmunity has been associated with miscarriage and some adverse pregnancy outcomes, research continues to explore whether thyroid antibodies themselves contribute directly or whether they are markers of a broader underlying autoimmune process.

Understanding this distinction is central to evidence-based care and will be explored in the next section

Hashimoto’s Thyroiditis and Fertility

A couple planning pregnancy with subtle thyroid illustration or fertility consultation scene.

One of the commonest questions women ask after being diagnosed with Hashimoto’s thyroiditis is:

“Will this stop me becoming pregnant?”

The answer is reassuring for most women.

Many women with Hashimoto’s thyroiditis conceive naturally and go on to have healthy pregnancies. However, autoimmune thyroid disease can affect fertility through several different mechanisms, particularly if thyroid hormone production becomes impaired.

Importantly, fertility is influenced by far more than thyroid function alone. Age, ovarian reserve, body weight, lifestyle, male factors, uterine abnormalities and other hormonal conditions all contribute. For this reason, thyroid disease should always be assessed as part of a broader fertility evaluation rather than in isolation.

Why Thyroid Hormones Matter

 

Thyroid hormones influence almost every stage of reproduction.

They affect:

Even relatively mild hypothyroidism can alter reproductive physiology.

Women may experience:

Fortunately, correcting overt hypothyroidism usually restores normal fertility in many women.

Can Hashimoto’s Affect Egg Quality?

This remains an area of active research.

Current evidence suggests that thyroid hormones contribute to normal follicular maturation within the ovary. Women with untreated hypothyroidism may have impaired follicular development, although the precise relationship between thyroid autoimmunity and egg quality remains uncertain.

Studies examining women with normal thyroid function but positive anti-TPO antibodies have produced mixed results. Some suggest slightly reduced ovarian reserve or poorer IVF outcomes, whereas others demonstrate little or no independent effect once age and thyroid function are taken into account.

Overall, thyroid hormone deficiency appears more important than antibody positivity alone.

Does Hashimoto’s Affect Implantation?

Successful implantation depends upon a healthy endometrium, normal embryo development and complex immune interactions within the uterus.

Researchers have proposed several mechanisms whereby autoimmune thyroid disease could influence implantation:

However, direct evidence remains limited.

Current guidance does not support routine immunological treatments solely because anti-TPO antibodies are present.

Anti-TPO Antibodies and Miscarriage

This is one of the most studied—and most misunderstood—areas in reproductive medicine.

Over the last two decades, many observational studies have reported that women with thyroid autoantibodies appear more likely to experience miscarriage than women without thyroid antibodies.

Several meta-analyses have demonstrated an association between thyroid autoimmunity and pregnancy loss.

However, an association does not necessarily prove causation.

This distinction is fundamental.

Women with thyroid antibodies may differ from antibody-negative women in many ways, including age, underlying autoimmune predisposition and subtle thyroid dysfunction that is not fully reflected by a single blood test.

Consequently, researchers continue to debate whether thyroid antibodies directly contribute to miscarriage or whether they simply identify women who have a higher baseline risk.

Possible Mechanisms

Several theories have been proposed.

1. Progressive thyroid insufficiency

The thyroid gland may be functioning adequately before pregnancy but unable to meet the increased hormonal demands once pregnancy begins.

Even small reductions in available thyroid hormone during early placental development could theoretically contribute to pregnancy loss.

2. Autoimmune activation

Rather than directly attacking the pregnancy, thyroid antibodies may indicate a broader disturbance in immune regulation.

Women with one autoimmune condition are statistically more likely to develop others.

This has prompted investigation into shared pathways between thyroid autoimmunity and recurrent miscarriage.

3. Placental effects

Some researchers have suggested that thyroid autoimmunity may influence placental development or trophoblast invasion.

Evidence supporting this mechanism remains limited.

4. Co-existing autoimmune disease

Women with Hashimoto’s thyroiditis have increased rates of other autoimmune conditions including:

These associated conditions may independently influence reproductive outcomes.

What Does the Evidence Show?

Overall, evidence suggests that:

Most importantly:

The majority of women with anti-TPO antibodies will still have successful pregnancies.

This is an essential message during counselling.

Positive antibodies should never be interpreted as meaning miscarriage is inevitable.

Should Everyone with Positive Anti-TPO Antibodies Receive Levothyroxine?

This question has transformed clinical practice over the past decade.

Historically, many clinicians prescribed levothyroxine to women with positive thyroid antibodies in the hope of reducing miscarriage.

More recent large randomised controlled trials have challenged this approach.

The TABLET Trial, conducted in the United Kingdom, evaluated euthyroid women with thyroid antibodies who were attempting conception or undergoing fertility treatment.

Levothyroxine did not significantly improve live birth rates compared with placebo.

Other high-quality studies have reached similar conclusions.

Consequently, current guidelines no longer recommend routine levothyroxine treatment solely because thyroid antibodies are present if thyroid function is normal.

However, this does not mean levothyroxine is never appropriate.

Treatment may still be considered in selected women, particularly when:

Management should therefore be individualised.

Hashimoto’s and Recurrent Miscarriage

Recurrent miscarriage is usually defined as three or more consecutive pregnancy losses, although many specialist clinics begin investigation after two miscarriages, particularly when maternal age is increasing.

At Innermost Healthcare, thyroid assessment forms one component of a comprehensive recurrent miscarriage evaluation.

This may include:

Importantly, thyroid antibodies rarely represent the sole explanation for recurrent miscarriage.

Comprehensive assessment helps identify potentially treatable contributing factors while avoiding unnecessary interventions.

IVF and Assisted Reproduction

Thyroid function is particularly important before assisted conception.

Most fertility clinics aim to optimise thyroid function before commencing IVF.

Women already taking levothyroxine often require careful dose adjustment before embryo transfer.

Current evidence suggests:

Consequently, thyroid optimisation should be personalised rather than protocol-driven.

Should Anti-TPO Antibodies Be Tested Before Pregnancy?

There is no recommendation for universal thyroid antibody screening in all women planning pregnancy.

However, testing may be appropriate when women have:

Testing should always be interpreted alongside thyroid function rather than in isolation.

Pre-Pregnancy Optimisation

For women known to have Hashimoto’s thyroiditis who are planning pregnancy, pre-conception assessment offers an opportunity to optimise health before conception occurs.

Key areas include:

✓ Review of thyroid function

✓ Assessment of levothyroxine dose

✓ Optimisation of TSH where appropriate

✓ Folic acid supplementation

✓ Review of vitamin D status

✓ General nutritional assessment

✓ Review of other medications

✓ Smoking cessation

✓ Weight optimisation

✓ Assessment for associated autoimmune conditions when indicated

Key Facts

Women with Hashimoto’s thyroiditis should not assume that pregnancy will be difficult or unsuccessful.

Current evidence supports a balanced and reassuring approach:

Pregnancy Management, Monitoring and Treatment

Planning Pregnancy with Hashimoto’s Thyroiditis

Pregnancy planning consultation with thyroid health illustration.

The ideal time to optimise thyroid health is before conception. Many of the critical events in fetal development occur during the first few weeks of pregnancy, often before a woman knows she is pregnant.

For women with known Hashimoto’s thyroiditis, a pre-pregnancy consultation provides an opportunity to review thyroid function, optimise medication where required and discuss appropriate monitoring during pregnancy.

This proactive approach aims to minimise the risk of untreated hypothyroidism during early pregnancy while avoiding unnecessary treatment in women whose thyroid function remains normal.

Pre-Conception Assessment

At Innermost Healthcare, assessment is tailored to the individual but may include:

Clinical Review

Blood Tests

Recommended investigations may include:

Investigation	Why it is Important
TSH	Primary assessment of thyroid function
Free T4	Assesses circulating thyroid hormone
Anti-TPO antibodies	Confirms thyroid autoimmunity
Anti-thyroglobulin antibodies	Helpful in selected cases
Vitamin D	Deficiency is common in the UK
Ferritin	Iron deficiency may contribute to fatigue
Vitamin B12	Autoimmune gastritis may coexist
Folate	Essential before conception

Where clinically indicated, further investigations may also be appropriate.

Target TSH Before Pregnancy

Although recommendations vary slightly between professional organisations, many endocrinologists aim for a TSH below 2.5 mIU/L before conception in women receiving levothyroxine.

This target provides a margin of safety because thyroid hormone requirements frequently increase soon after pregnancy begins.

It is important to recognise that TSH targets should always be interpreted alongside free T4 levels, symptoms and the individual clinical context.

What Happens to the Thyroid During Pregnancy?

Pregnancy places unique physiological demands upon the thyroid gland.

Several hormonal changes occur simultaneously.

Human Chorionic Gonadotrophin (hCG)

The pregnancy hormone hCG has a weak thyroid-stimulating effect.

During early pregnancy this may temporarily lower TSH concentrations.

Oestrogen

Rising oestrogen increases production of thyroid-binding globulin.

As more thyroid hormone becomes protein-bound, the thyroid gland must produce additional hormone to maintain adequate free hormone levels.

Placental Metabolism

The placenta metabolises maternal thyroid hormones, further increasing maternal requirements.

Increased Iodine Requirement

Pregnancy increases renal iodine loss while simultaneously increasing thyroid hormone production.

Adequate—but not excessive—iodine intake therefore becomes increasingly important.

Why the First Trimester is So Important

One of the most important concepts in obstetric medicine is that the developing fetal thyroid gland is not fully functional during early pregnancy.

During approximately the first trimester, the fetus relies almost entirely upon maternal thyroid hormone.

Adequate maternal thyroxine supports:

This explains why untreated overt hypothyroidism early in pregnancy can have important consequences.

Women Already Taking Levothyroxine

Women who are already receiving levothyroxine before pregnancy usually require an increase in dosage once pregnancy is confirmed.

Professional guidance generally recommends contacting the healthcare professional responsible for thyroid management promptly after a positive pregnancy test.

Many endocrinologists advise increasing the weekly levothyroxine dose immediately while arranging repeat thyroid function testing.

Dose adjustment should always be individualised.

Women Not Receiving Levothyroxine

Women with positive thyroid antibodies but normal thyroid function often require monitoring rather than immediate treatment.

During pregnancy thyroid reserve may become insufficient.

For this reason, periodic thyroid function testing is usually recommended throughout pregnancy.

Treatment decisions should be guided primarily by thyroid function rather than antibody positivity alone.

Monitoring During Pregnancy

Pregnancy monitoring timeline.

First Trimester

Objectives:

Blood tests:

Repeat testing is commonly recommended every four to six weeks during the first half of pregnancy when medication changes are most likely.

Second Trimester

As pregnancy progresses, thyroid hormone requirements usually stabilise.

Management focuses upon:

Third Trimester

Later pregnancy assessment concentrates upon:

Ultrasound During Pregnancy

Hashimoto’s thyroiditis itself is not an indication for additional fetal ultrasound examinations if thyroid function remains normal and there are no obstetric concerns.

However, women with overt hypothyroidism or other pregnancy complications may require additional surveillance depending upon the wider clinical picture.

Ultrasound assessment should therefore always be individualised.

Selenium

Selenium is an essential trace element involved in thyroid hormone metabolism.

Several studies have investigated whether selenium supplementation reduces thyroid antibody concentrations.

Some trials demonstrate modest reductions in anti-TPO antibody levels.

However:

Current UK guidance does not recommend routine selenium supplementation for all women with Hashimoto’s thyroiditis.

Nevertheless, ensuring an adequate dietary intake is sensible.

Good dietary sources include:

Vitamin D

Vitamin D deficiency is common throughout the UK.

Several observational studies have reported an association between vitamin D deficiency and autoimmune thyroid disease.

However, whether supplementation alters progression of Hashimoto’s thyroiditis remains uncertain.

Women planning pregnancy should nevertheless maintain adequate vitamin D levels because supplementation is recommended more broadly during pregnancy for maternal and fetal bone health.

Iodine

Iodine deserves special consideration.

Adequate iodine intake is essential for thyroid hormone production.

However, excessive iodine intake may exacerbate autoimmune thyroid disease in susceptible individuals.

For most women:

are sufficient.

High-dose iodine supplements should generally be avoided unless specifically advised by an experienced clinician.

Iron

Iron deficiency deserves particular attention because:

Correcting iron deficiency may improve overall wellbeing even when thyroid function is stable.

Folic Acid

Women planning pregnancy should continue standard folic acid recommendations.

Higher doses (5 mg daily) may be appropriate for women with additional recognised indications, such as certain medical conditions or medications, in accordance with national guidance.

Lifestyle Measures

Although no diet has been proven to cure Hashimoto’s thyroiditis, several lifestyle measures support general health.

These include:

Patients should be cautious about claims made on social media or commercial websites regarding “reversing” autoimmune thyroid disease through restrictive diets or expensive supplements.

Current scientific evidence does not support many of these claims.

Is a Gluten-Free Diet Helpful?

This remains a common question.

Women with confirmed coeliac disease should follow a strict gluten-free diet.

However, routine gluten avoidance for everyone with Hashimoto’s thyroiditis is not currently recommended by major professional organisations.

Research continues, but evidence demonstrating improved fertility or pregnancy outcomes in women without coeliac disease remains insufficient.

Multidisciplinary Care

Management is often most effective when different healthcare professionals work together.

Depending upon individual circumstances this may include:

The degree of specialist involvement depends upon the severity of thyroid disease, previous pregnancy history and associated medical conditions.

Key Messages

Part 4 – After Delivery, Long-Term Care, Frequently Asked Questions and References

Life After Pregnancy

Mother holding newborn with subtle thyroid illustration.

For most women, thyroid care does not end when the baby is born. Pregnancy places significant physiological demands on the thyroid gland, and hormone requirements often change rapidly after delivery.

Women with Hashimoto’s thyroiditis should therefore continue to have appropriate follow-up after birth to ensure thyroid function remains well controlled and medication is adjusted if necessary.

The postpartum period is also a time when new thyroid problems may first become apparent.

Postpartum Thyroiditis

Postpartum thyroiditis is a separate autoimmune condition that occurs in approximately 5–10% of women after pregnancy. The risk is substantially higher in women with positive anti-thyroid antibodies, particularly anti-TPO antibodies.

The condition usually develops within the first year after delivery and may follow one of several patterns:

Not every woman experiences all phases.

Symptoms

Symptoms vary depending upon the stage of the condition.

Thyrotoxic phase

Women may experience:

Because these symptoms may overlap with the normal demands of caring for a newborn, postpartum thyroiditis may initially be overlooked.

Hypothyroid phase

Later symptoms may include:

Again, these symptoms overlap with normal postnatal recovery and postnatal depression, highlighting the importance of appropriate thyroid testing when symptoms are persistent or severe.

Breastfeeding

Women frequently ask whether levothyroxine is safe while breastfeeding.

The answer is yes.

Levothyroxine is considered compatible with breastfeeding and should be continued whenever clinically indicated.

Maintaining normal maternal thyroid function benefits both maternal wellbeing and successful breastfeeding.

Women should not stop levothyroxine after delivery unless advised by the clinician managing their thyroid condition.

Reducing Levothyroxine After Delivery

Many women who increased their levothyroxine dose during pregnancy require dose reduction after birth.

The timing and extent of adjustment depends upon:

Repeat thyroid function testing is therefore recommended following delivery, with subsequent dose adjustment based upon clinical assessment rather than a predetermined schedule.

Future Pregnancies

Women with Hashimoto’s thyroiditis who are planning another pregnancy should ideally undergo reassessment before conception.

This allows:

Women who required levothyroxine dose increases during one pregnancy often require similar adjustments in future pregnancies.

Long-Term Outlook

The long-term prognosis for Hashimoto’s thyroiditis is generally excellent.

Although autoimmune damage to the thyroid gland usually progresses slowly, modern treatment with levothyroxine is highly effective when hypothyroidism develops.

Most women lead entirely normal lives, have successful pregnancies and remain healthy with appropriate monitoring.

Frequently Asked Questions

Can I become pregnant if I have Hashimoto’s thyroiditis?

Yes.

Most women with Hashimoto’s thyroiditis conceive naturally and have healthy pregnancies.

The most important consideration is ensuring thyroid function is appropriately monitored and treated when necessary.

Will Hashimoto’s cause infertility?

Not usually.

Untreated hypothyroidism can reduce fertility, but most women with well-controlled thyroid function conceive successfully.

Do positive anti-TPO antibodies mean I will miscarry?

No.

Although thyroid autoimmunity is associated with an increased risk of miscarriage, most women with positive anti-TPO antibodies will have successful pregnancies.

Positive antibodies should never be interpreted as meaning miscarriage is inevitable.

Should everyone with anti-TPO antibodies take levothyroxine?

No.

Current evidence does not support routine levothyroxine treatment for all euthyroid women with positive anti-TPO antibodies.

Treatment decisions should be individualised.

Should my TSH be below 2.5 before pregnancy?

For women receiving levothyroxine, many clinicians aim for a TSH below approximately 2.5 mIU/L before conception.

However, treatment decisions should always consider the complete clinical picture.

Can Hashimoto’s harm my baby?

When thyroid function is appropriately monitored and treated where necessary, the outlook is generally excellent.

Untreated overt hypothyroidism carries greater risks than autoimmune thyroid disease itself.

Is selenium recommended?

Routine selenium supplementation is not currently recommended for all women with Hashimoto’s thyroiditis.

A healthy balanced diet usually provides adequate selenium.

Should I avoid gluten?

Only if you have coeliac disease or another recognised medical indication.

Routine gluten-free diets are not currently recommended solely because Hashimoto’s thyroiditis is present.

Can Hashimoto’s be cured?

There is currently no cure for Hashimoto’s thyroiditis.

However, hypothyroidism can usually be managed very effectively with levothyroxine when treatment is required.

Will I always need medication?

Not necessarily.

Some women remain euthyroid for many years despite positive thyroid antibodies.

Others gradually develop hypothyroidism requiring lifelong treatment.

Regular monitoring helps determine when treatment becomes appropriate.

Key Take-Home Messages

Key Facts at a Glance

Consultant-Led Assessment at Innermost Healthcare

At Innermost Healthcare, we provide consultant-led assessment for women with thyroid disease before, during and after pregnancy.

Our approach may include:

Every woman is different, and recommendations should be tailored to her medical history, reproductive goals and laboratory findings.

References

This article is based on current evidence and established professional guidance, including:

Conclusion

Hashimoto’s thyroiditis is common, and for many women it is diagnosed at a time when they are planning a family or seeking answers after fertility difficulties or pregnancy loss. Although thyroid autoimmunity is associated with an increased risk of certain reproductive complications, it is important to place these risks in context. Most women with Hashimoto’s thyroiditis conceive successfully and go on to have healthy pregnancies.

Modern management focuses on identifying women who will benefit from treatment, avoiding unnecessary interventions in those who remain euthyroid, and providing appropriate monitoring throughout pregnancy and after delivery. Evidence continues to evolve, and management should be guided by current research, professional recommendations and individual clinical circumstances rather than antibody status alone.

If you have Hashimoto’s thyroiditis and are planning a pregnancy, experiencing fertility problems or have suffered recurrent miscarriage, consultant-led assessment can help clarify your thyroid status, discuss the latest evidence and develop a personalised management plan.