Thyroid ultrasound examination in a pregnant woman to assess thyroid health during pregnancy

Thyroid and Miscarriage: What the Research Really Shows

Miscarriage is one of the most painful experiences a person can endure, and one of the most isolating.

When it happens, the questions arrive almost immediately:

Was it something I did?
Was my body trying to tell me something?
Could this happen again?

For many people, those questions go unanswered for months or even years.

And for a surprising number of them, the missing piece lies in a part of the body that’s often overlooked in fertility care: the thyroid.

Research increasingly shows a meaningful connection between thyroid health and miscarriage, yet many patients are never fully evaluated. Others are told their labs are “normal,” even when those values may not be optimal for pregnancy.

Let’s break down what the science actually says, what truly matters for fertility, and what steps you can take to advocate for your health, without blame, fear, or overwhelm.

Thyroid and Miscarriage

Thyroid hormones play a critical role in early pregnancy and fetal development
Both hypothyroidism and subclinical thyroid dysfunction increase miscarriage risk
Elevated TSH levels, even within “normal” lab ranges, may impact implantation and pregnancy maintenance
Thyroid autoimmunity (like Hashimoto’s) is linked to recurrent miscarriage, even when hormone levels appear normal
Early screening, proper management, and individualized care can significantly reduce risk

This is why thyroid testing is a cornerstone of evidence-based fertility care.

Why Thyroid Health Matters So Much in Early Pregnancy

The thyroid gland produces hormones that regulate metabolism, energy production, and cellular growth throughout the body. But during early pregnancy, its role becomes even more critical.

Before the placenta is fully developed, usually around 10–12 weeks, the embryo relies entirely on the pregnant person’s thyroid hormones.

If thyroid function is impaired during this window, the body may struggle to:

Support implantation
Maintain adequate progesterone levels
Regulate immune tolerance to the pregnancy
Sustain early fetal development

This is where the link between thyroid dysfunction and miscarriage becomes clinically significant.

Understanding TSH, Thyroid Hormones, and Pregnancy

Most thyroid screening begins, and often ends, with a single test: TSH (thyroid-stimulating hormone).

In fertility care, TSH and infertility are closely connected because TSH reflects how hard the brain is working to tell the thyroid to produce hormones.

When TSH is elevated, it often signals that the thyroid is underperforming.

General vs. Pregnancy-Optimal TSH Ranges

Many laboratories list a “normal” TSH range of up to 4.0 or even 5.0.

However, fertility and pregnancy research show something different:

Optimal TSH for conception and early pregnancy: ~0.5–2.5
TSH levels above this range are associated with a higher miscarriage risk

This means someone can be told their thyroid is “normal” while still being at increased risk for pregnancy loss.

Hypothyroidism and Miscarriage Risk

Hypothyroidism, when the thyroid does not produce enough hormone, has been consistently linked to miscarriage in medical literature.

Potential effects include:

Poor implantation
Increased systemic inflammation
Hormonal imbalance
Impaired placental development

Studies show that untreated or inadequately treated hypothyroidism significantly increases the risk of early pregnancy loss.

The encouraging part?

When hypothyroidism is identified early and treated appropriately, miscarriage risk can often be reduced to near baseline levels.

This makes thyroid optimization one of the most impactful and modifiable factors in fertility care.

Subclinical Hypothyroidism: The “Gray Area” That Matters

Subclinical hypothyroidism occurs when:

TSH is elevated
Free T3 and T4 appear within lab “normal” ranges

This is one of the most debated topics in the thyroid-miscarriage conversation—and one of the most important.

Research suggests:

Even mild TSH elevations can negatively impact pregnancy outcomes
Miscarriage risk is higher when thyroid antibodies are present
Early treatment improves outcomes in many patients

This is why fertility-focused providers often look beyond standard lab cutoffs and assess thyroid function through a pregnancy-specific lens.

Thyroid Autoimmunity and Recurrent Miscarriage

One of the strongest links between thyroid and recurrent miscarriage involves autoimmune thyroid disease, most commonly Hashimoto’s thyroiditis.

Key findings from research:

Individuals with thyroid antibodies experience higher miscarriage rates
This risk exists even when TSH and thyroid hormones appear normal
Immune dysregulation, not just hormone deficiency, plays a role

In other words, the immune system itself can interfere with pregnancy maintenance, independent of hormone levels.

This is why comprehensive thyroid testing, including thyroid antibodies, is essential after unexplained or recurrent pregnancy loss.

Why Thyroid Issues Are Often Missed

Many people navigating miscarriage share similar experiences:

“All my labs were normal.”
“No one tested my thyroid beyond TSH.”
“I was told to just try again.”

Traditional screening often stops at basic labs, missing:

Thyroid antibodies (TPO, TgAb)
Free hormone levels
Functional patterns affecting fertility

This gap is where specialized fertility consulting or working with a fertility nurse practitioner can make a meaningful difference.

Professional Insight: What We See in Practice

In clinical fertility practice, thyroid-related issues are among the most common modifiable contributors to miscarriage.

What’s important to understand is this:

Most losses related to thyroid dysfunction are not inevitable.

When thyroid health is properly evaluated, optimized before conception, and monitored closely in early pregnancy, outcomes improve significantly.

That’s why thyroid assessment is a foundational part of functional, evidence-based fertility care, not an afterthought.

What You Can Do If You’re Concerned About Thyroid and Miscarriage

If you’ve experienced a miscarriage or are preparing for pregnancy, these steps can help you advocate for your health:

Request comprehensive thyroid testing (not TSH alone)
Review results with a provider familiar with fertility-specific ranges
Address inflammation, nutrient deficiencies, and immune balance
Monitor thyroid levels regularly during early pregnancy

Small, informed adjustments can make a profound difference.

Frequently Asked Questions About Thyroid and Miscarriage

Can thyroid problems cause miscarriage?
Yes. Both overt and subclinical thyroid dysfunction are linked to increased miscarriage risk.

Can miscarriage occur even if thyroid labs are “normal”?
Yes. Standard lab ranges may not reflect pregnancy-optimal levels, especially when thyroid antibodies are present.

Does treating thyroid issues reduce miscarriage risk?
Research shows that appropriate treatment and monitoring significantly improve pregnancy outcomes.

Should thyroid be tested after a miscarriage?
Absolutely. Thyroid evaluation is recommended after unexplained or recurrent pregnancy loss.

Final Thoughts: Knowledge Is Not Blame—It’s Power

Learning about the connection between thyroid and miscarriage is not about finding fault; it’s about finding clarity in a space that often feels overwhelming and uncertain.

At Katy Poole Wellness, care is grounded in the belief that informed, compassionate guidance can change how people experience their fertility journey. For many, understanding and optimizing thyroid health becomes the missing piece that transforms unanswered questions into confidence and loss into a clearer path forward.

You deserve answers that make sense.
You deserve care that looks beyond “normal” labs.
And you deserve support rooted in both science and deep respect for your lived experience.