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If you have hypothyroidism or Hashimoto's thyroiditis and you're pregnant — or hoping to become pregnant — you've probably had more than a few anxious conversations with your doctor about TSH levels, thyroid medication doses, and all the ways thyroid disease can complicate an already complex journey. For years, patients have been diagnosed and treated according to guidelines that date back to 2017. Now, for the first time in nearly a decade, those guidelines for thyroid treatment during pregnancy have been completely overhauled.

In May 2026, the American Thyroid Association (ATA) published sweeping new recommendations covering thyroid disease across the entire reproductive spectrum — before conception, during pregnancy, and in the postpartum period. The ATA guidelines document, endorsed by 12 international medical societies including the American College of Obstetricians and Gynecologists and the Endocrine Society, represents the most rigorous and comprehensive guidance ever produced on this subject.

For Hashimoto’s and hypothyroid patients, the updates are significant — and in some cases, genuinely reassuring. Here's what you need to know.

Pregnancy places extraordinary demands on your thyroid gland. From the earliest weeks of pregnancy, your body needs substantially more thyroid hormone — both to sustain your own metabolism during a period of dramatic change, and to support your baby's developing brain, which depends heavily on your thyroid hormone – especially during the first trimester when the fetal thyroid is unable to produce its own thyroid hormone.

For women with hypothyroidism (including Hashimoto's thyroiditis, the autoimmune condition that destroys thyroid tissue over time), this increased demand can push an otherwise well-controlled condition into imbalance. Untreated or inadequately treated overt hypothyroidism during pregnancy has been linked to a higher risk of miscarriage, gestational hypertension, preterm birth, and a reduced IQ in offspring.

The good news: women who achieve good thyroid control on levothyroxine have the same pregnancy and birth outcomes as women without any thyroid disease at all. The goal of these new guidelines is to help you and your doctor get — and stay — in that well-controlled group.

One of the most confusing aspects of thyroid management in pregnancy is figuring out what a "normal" TSH level actually looks like. Pregnancy naturally shifts thyroid hormone physiology in ways that make standard reference ranges unreliable. The guidelines address this directly — and with meaningful nuance.

Why pregnancy changes the goalposts

During early pregnancy, a hormone called human chorionic gonadotropin (hCG) — the same hormone that turns a pregnancy test positive — stimulates the thyroid gland to produce more hormone. This causes TSH levels to drop, sometimes significantly, during the first trimester. It's normal and expected. Additionally, pregnancy increases the proteins that bind and transport thyroid hormone in your bloodstream, which further shifts the levels you'd see on a lab report.

This is why a thyroid-stimulating hormone level below 0.4 mU/L — which would suggest hyperthyroidism in a non-pregnant person — is actually common and normal in the first trimester. Interpreting a pregnant woman's TSH using non-pregnancy ranges leads to overdiagnosis and overtreatment.‍

At-a-glance: TSH level target ranges by stage

A critical note on free thyroxine (free T4): the guidelines acknowledge that free T4 testing during pregnancy is complicated. Pregnancy-related changes in blood proteins can make free T4 readings unreliable, especially in the second half of pregnancy. For this reason, the guidelines emphasize that TSH remains the most reliable indicator of thyroid status during pregnancy. When TSH and free T4 seem to conflict, prioritize the TSH.

Not every elevated TSH level during pregnancy means the same thing — or requires the same response. The 2026 guidelines make important distinctions based on how high the TSH is, when in pregnancy it's detected, and whether the elevation is persistent.

Overt hypothyroidism (TSH ≥ 6 mU/L in pregnancy)

A TSH level at or above 6 mU/L during pregnancy is classified as overt hypothyroidism and should always be treated with levothyroxine. At this level, the guidelines recommend starting LT4 promptly. For women newly diagnosed during pregnancy, initial dosing may follow a full-replacement approach (1.5–1.7 mcg/kg/day) plus an additional 20–30% increase to account for gestational demands.

Most women with pre-existing hypothyroidism who are already on levothyroxine will need a dose increase of roughly 25% by week 12 of pregnancy, and approximately 50% by week 20. After delivery, the dose can typically return to the pre-pregnancy level, with a follow-up TSH level check around six weeks postpartum.

Important: One size does not fit all

The guidelines caution that women with a pre-pregnancy TSH level below 1.5 mU/L, or those already on higher doses (above 100 mcg/day), may have a higher risk of overtreatment if they apply a standard dose increase. Work with your healthcare provider to tailor dose adjustments based on your individual thyroid levels and response.

Mild overt hypothyroidism (TSH above upper limit but below 6 mU/L)

Here, the guidelines introduce an important new nuance. If your TSH level is elevated above the pregnancy upper limit but still below 6 mU/L, the 2026 guidelines say it may be reasonable to confirm the abnormality with a repeat test before immediately starting treatment — provided this is consistent with your preferences after informed counseling.

Why? Because new research shows that mild TSH elevations in pregnancy are often transient. Studies find that only about half of these cases persist when TSH is retested just one to three weeks later, and even fewer persist into the third trimester. This doesn't mean watchful waiting is always appropriate — your doctor will weigh the risks carefully with you — but it does mean that not every mildly elevated TSH requires immediate medication.

Subclinical hypothyroidism (TSH above the upper limit with normal free T4)

Subclinical hypothyroidism — where TSH is elevated but free T4 remains normal — affects roughly 3 to 6% of pregnant women. The evidence on treatment benefits is genuinely mixed, and the guidelines reflect that complexity.

The clearest signal from the research is timing: levothyroxine treatment for subclinical hypothyroidism appears most likely to be beneficial when started during the first trimester, when thyroid hormone is most critical for fetal brain development. Multiple large clinical trials found no benefit when treatment was started later — one major US trial, for example, found no improvement in obstetric outcomes or child IQ at age five when LT4 was started at an average of 17 weeks' gestation.

For first-trimester subclinical hypothyroidism, the guidelines recommend a shared decision-making approach: your doctor should counsel you on the small but real risks of untreated subclinical hypothyroidism, the uncertainty around treatment benefits, and the risk of overtreatment. If you and your doctor decide to proceed with LT4, starting at a low dose (25–75 mcg/day, depending on your weight and TSH level) is advised to avoid over-correction.

For subclinical hypothyroidism diagnosed after the first trimester, the evidence supporting treatment is weak. The guidelines do not recommend routine LT4 initiation in this context.

Hashimoto's thyroiditis — in which the immune system attacks thyroid tissue and the thyroid gland — is the most common cause of hypothyroidism in women of reproductive age, and it's one of the most common questions thyroid patients have going into pregnancy. The 2026 guidelines offer important new clarity.

TPOAb positivity alone is not enough to warrant treatment

Many women with Hashimoto's thyroiditis are "euthyroid TPOAb positive" — meaning their thyroid is still functioning normally (with a normal TSH level). Still, they test positive for thyroid peroxidase antibodies (TPO antibodies, or TPOAb), the immune markers of Hashimoto's. For years, there was debate about whether women with thyroid autoimmunity should receive low-dose levothyroxine to protect against pregnancy complications.

The 2026 guidelines settle this question decisively: no. Three large, high-quality randomized clinical trials published since the 2017 guidelines all reached the same conclusion: giving LT4 to euthyroid women with thyroid antibodies — whether before or during early pregnancy — does not improve fertility, reduce miscarriage risk, or prevent preterm birth.

This is a significant finding. It suggests that the slightly elevated miscarriage and preterm birth risk seen in TPOAb-positive women with thyroid autoimmunity is not driven by thyroid hormone deficiency, and therefore cannot be corrected by adding more thyroid hormone. The underlying mechanism — likely involving other aspects of immune dysregulation — remains under investigation.

What this means for you

If you have Hashimoto's thyroiditis but your thyroid function is currently optimal for conception, you do NOT need to start levothyroxine to improve your pregnancy chances or reduce miscarriage risk. However, you should be monitored carefully, because about 7–9% of euthyroid women who are positive for thyroid antibodies will develop subclinical or overt hypothyroidism before or during pregnancy. Your doctor should recheck your TSH every 3–6 months while you are trying to conceive, and continue frequent monitoring throughout pregnancy.

TPOAb status no longer drives treatment decision-making in subclinical hypothyroidism

This is another major update. In the 2017 guidelines, thyroid antibody positivity was used as a deciding factor in whether to treat subclinical hypothyroidism with levothyroxine. The new guidelines remove that distinction. The difference in pregnancy risk between TPOAb-positive and TPOAb-negative subclinical hypothyroidism is small enough that the treatment decision should be based on other factors — primarily timing, TSH level, and patient preference — rather than antibody status.

Selenium, inositol, and other supplements: still no clear evidence

Many patients with Hashimoto's have heard that selenium supplementation might help reduce antibody levels. The 2026 guidelines reviewed the available evidence and found no data supporting the use of selenium, intravenous immunoglobulins, glucocorticoids, or other immune-modulating supplements to improve pregnancy outcomes or prevent progression to hypothyroidism. This area needs more research, but for now, these are not recommended.

Beyond the individual clinical recommendations, the 2026 guidelines represent a fundamental shift in how thyroid experts approach pregnancy management. Here are the most important changes and what they mean in practice.

1. Treatment for euthyroid antibody-positive women is no longer recommended

Old guidance (2017): Some women with positive TPO antibodies and thyroid-stimulating hormone above 2.5 mU/L were offered levothyroxine, even without overt hypothyroidism, on the theory that it might reduce miscarriage risk.

New guidance (2026): Three definitive randomized trials showed no benefit for women with an autoimmune disorder. Levothyroxine should not be offered to women who are euthyroid (normal TSH), even if they are TPOAb positive, except in the context of a clinical trial.

Why it matters: This change spares a significant number of women from taking a medication that carries risks of overtreatment — including heart palpitations, bone density loss, and anxiety — without proven benefit.

2. Timing of treatment for subclinical hypothyroidism is now central to decision-making

Old guidance (2017): The decision to treat subclinical hypothyroidism was largely based on TSH level and TPOAb status.

New guidance (2026): Timing is now the primary factor. Treatment is most likely beneficial when started in the first trimester. For subclinical hypothyroidism identified in the second trimester or before delivery, the evidence does not support starting LT4.

Why it matters: This nuanced approach prevents both undertreatment in early pregnancy (when thyroid hormones matter most for fetal brain development) and overtreatment later, when the benefit window has likely passed.

3. Confirmation of TSH abnormalities before treating

Old guidance (2017): A single elevated TSH level reading was often sufficient to initiate treatment.

New guidance (2026): For mild TSH elevations (below 6 mU/L), clinicians are now encouraged to confirm the abnormality with a repeat thyroid function testing 1–3 weeks later before starting medication, because at least half of these mild elevations resolve spontaneously.

Why it matters: This protects patients from unnecessary treatment while still ensuring that persistent, meaningful hypothyroidism is caught and treated.

4. Updated risk factor list for who should be screened

Old guidance (2017): The list of risk factors used to determine which pregnant women should have their thyroid tested included maternal age, BMI, and parity.

New guidance (2026): Age, BMI, and parity have been removed from the risk factor list because new data showed they added little diagnostic value. The refined list now focuses on factors with stronger predictive power, including a personal history of thyroid disease, known TPOAb positivity, Type 1 diabetes or other autoimmune disease, prior thyroid surgery or radiation, family history of autoimmune thyroid disease, and prior pregnancy complications.

Why it matters: A cleaner risk-factor list helps clinicians identify who truly needs testing without creating the impression that virtually every pregnant woman requires thyroid screening.

5. Desiccated thyroid and liothyronine: not recommended in pregnancy

Old and new guidance agree, but the 2026 guidelines make this more explicit: women using desiccated thyroid extract (like Armour Thyroid) or liothyronine (T3 therapy) should switch to levothyroxine monotherapy before trying to conceive.

Why it matters: The fetal brain depends heavily on maternal T4 crossing the placenta and being locally converted to T3 within fetal brain tissue. T3 itself cannot cross the fetal blood-brain barrier effectively. Desiccated thyroid and T3-containing preparations provide relatively high T3 and lower T4 levels, which could deprive the fetal brain of the raw materials it needs. This is considered a Good Practice Statement — meaning all clinicians should follow it.

6. Clearer recommendations for iodine with stronger emphasis

The 2026 guidelines reinforce and sharpen the iodine supplementation guidance. Pregnant and breastfeeding women need 250 mcg of total iodine daily from all sources (food and supplements combined). Women who are planning pregnancy should ideally start iodine supplementation of 150 mcg/day at least three months before conception.

Women at higher risk of iodine deficiency — those who avoid dairy, don't use iodized salt, follow vegan diets, or live in regions with low iodine in the food supply — may need additional supplementation. The guidelines also caution against excessive iodine (supplements above 500 mcg/day), which can paradoxically cause thyroid dysfunction.

The guidelines place significant emphasis on the preconception period—and for good reason. Getting thyroid levels optimized before pregnancy begins gives you and your baby the best possible start.

• Get your TSH tested and aim for a level below 2.5 mU/L if you are already on levothyroxine.
• If you have subclinical hypothyroidism diagnosed before pregnancy, consider repeating the test 4–6 weeks later to confirm it's persistent before starting treatment.
• If you're on desiccated thyroid or T3 therapy, talk to your doctor about switching to levothyroxine monotherapy before you try to conceive.
• If you test positive for TPOAb but have a normal TSH, levothyroxine is not indicated — but ask your doctor about regular monitoring of your thyroid levels every 3–6 months while trying to conceive.
• Start iodine supplementation (150 mcg/day) ideally three or more months before conception.
• If you have infertility or a history of recurrent miscarriage, ask that your thyroid be tested as part of your work-up.

These guidelines give patients better tools to advocate for themselves. Here are questions that can help you have a more informed conversation:

• "What are my current thyroid levels, including my TSH, and is it appropriate for my stage of pregnancy or for conception planning?"
• "If my TSH is mildly elevated, should we retest before making a treatment decision?"
• "I have Hashimoto's thyroiditis with a normal TSH — how often should my thyroid be monitored during pregnancy?"
• "Is my lab using pregnancy-specific TSH reference intervals, or the standard non-pregnancy range?"
• "I'm currently on natural desiccated thyroid or T3/T4 combination treatment. Should I switch before trying to conceive?"
• "Am I getting enough iodine? Should I check my prenatal vitamin?"

The 2026 ATA guidelines represent a meaningful step forward for thyroid patients navigating pregnancy. They reflect a more individualized, evidence-based approach that considers not just your thyroid lab results, but when those results are measured, whether abnormalities are persistent, and which treatments have actually been shown to improve outcomes for mothers and babies.

For women with Hashimoto's thyroiditis, the clearest message is that thyroid antibody positivity alone should not determine treatment decisions. For women with hypothyroidism taking levothyroxine, the focus is on entering pregnancy with thyroid levels already optimized, monitoring thyroid function regularly throughout pregnancy, making timely medication adjustments when needed, and maintaining close communication with a knowledgeable healthcare provider.

At Paloma, we make it easier to put these recommendations into practice. Whether you're planning a pregnancy, actively trying to conceive, or already expecting, Paloma's thyroid specialists can help you optimize your thyroid levels before pregnancy, order comprehensive thyroid testing, closely monitor changes throughout each trimester, and adjust treatment as your body's needs evolve. With convenient at-home testing, virtual appointments, personalized care plans, and ongoing support from providers who specialize in thyroid disease, Paloma helps ensure you don't have to navigate pregnancy and thyroid care alone.

Thyroid disease in pregnancy is highly manageable. With the right preparation, expert guidance, and proactive monitoring, women with thyroid conditions can and do have healthy pregnancies and healthy babies. The updated guidelines provide stronger evidence than ever before—and Paloma is here to help you translate that evidence into confident, personalized care every step of the way.

What are the 2026 thyroid and pregnancy guidelines?

The 2026 American Thyroid Association guidelines provide updated recommendations for managing thyroid disease before conception, during pregnancy, and throughout the postpartum period. They incorporate nearly a decade of new research and are endorsed by multiple international medical organizations.

Why is thyroid health so important during pregnancy?

Thyroid hormone plays a critical role in supporting both maternal health and fetal brain development, especially during the first trimester. Untreated hypothyroidism has been linked to miscarriage, preterm birth, pregnancy complications, and impaired neurodevelopment in children.

What TSH level should I aim for if I'm planning a pregnancy?

Women taking levothyroxine who are trying to conceive should generally aim for a TSH level between 0.5 and 2.5 mU/L. This target helps create a safety margin for the increased thyroid hormone demands that occur early in pregnancy.

Do most women with hypothyroidism need more medication during pregnancy?

Yes. Most women with pre-existing hypothyroidism require a levothyroxine dose increase during pregnancy, often by about 25% by week 12 and as much as 50% by week 20. Regular monitoring is essential because individual needs vary.

Should a mildly elevated TSH always be treated immediately?

Not necessarily. The new guidelines suggest that some mild TSH elevations below 6 mU/L can be confirmed with repeat blood tests before treatment is started, because many cases normalize within a few weeks.

What is subclinical hypothyroidism during pregnancy?

Subclinical hypothyroidism occurs when TSH is elevated, but free T4 remains within the normal range. Treatment decisions should be individualized, with the strongest evidence of benefit when treatment is initiated in the first trimester.

If I have Hashimoto's antibodies but normal thyroid levels, do I need levothyroxine?

Current evidence says no. Large clinical trials found that giving levothyroxine to women who are TPO antibody-positive but have normal thyroid function does not improve fertility, reduce miscarriage risk, or prevent preterm birth.

How often should women with Hashimoto's thyroiditis be monitored while trying to conceive?

Women who are TPO antibody-positive but have normal thyroid levels should have a complete thyroid blood test panel every three to six months while attempting pregnancy. Monitoring should continue throughout pregnancy because some women will develop hypothyroidism during this time.

Can I stay on Armour Thyroid or T3 medication during pregnancy?

The guidelines recommend switching from natural desiccated thyroid medication or T3-containing therapies to levothyroxine before conception whenever possible, because T3 doesn't cross easily or well into the placenta. Levothyroxine provides the T4 needed for optimal fetal brain development.

How much iodine do I need before and during pregnancy?

The guidelines recommend a total daily iodine intake of 250 mcg during pregnancy and breastfeeding. Women planning pregnancy should ideally begin taking 150 mcg of supplemental iodine daily at least three months before conception.

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