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The Trump administration is warning about potential connections between acetaminophen (Tylenol), vaccines, and the risk of attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). While researchers and policymakers continue to debate these possible links, there is another factor that deserves equal attention: maternal hypothyroidism.

Over the past decade, researchers have increasingly explored the links between maternal thyroid status and developmental disorders such as ADHD and ASD, and there’s clear evidence that identifying and treating hypothyroidism in women before and during pregnancy is a significant risk factor that deserves attention.

In this article, we’ll look at the connections between maternal thyroid dysfunction during pregnancy, the links to ADHD and ASD, and what can be done to help reduce the risk.

Hypothyroidism occurs when the thyroid gland underproduces hormones, primarily thyroxine (T4) and triiodothyronine (T3). During pregnancy, this condition is especially concerning because, during the first trimester, the developing baby relies entirely on the mother’s thyroid hormone supply. These hormones guide brain development—helping neurons multiply, migrate to the right places, form synapses, and create structures needed for memory, attention, and movement. They also support myelination, which allows nerve signals to travel quickly and efficiently. Research shows that if a pregnant woman has untreated hypothyroidism, even at a mild or subclinical level, it can disrupt these processes and increase the risk of long-term neurodevelopmental and cognitive development issues, including ADHD and ASD in her child.

Hypothyroidism is easily missed in pregnant women. According to the American Thyroid Association, up to 60% of people with thyroid disease are unaware of their condition, meaning that a substantial number of pregnant women may have undiagnosed hypothyroidism. Pregnant women and their healthcare providers often assume that hypothyroidism symptoms such as fatigue, weight gain, and mood changes are related to the pregnancy. And routine pregnancy care in most countries – including the U.S. – does not include universal thyroid testing. Doctors usually check thyroid levels only if a woman has risk factors, like a personal or family history of thyroid disease, autoimmune conditions, symptoms of hypo/hyperthyroidism, or prior pregnancy complications.
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Why is thyroid hormone so crucial for the brain of a developing baby?

Thyroid hormones are crucial to brain development, especially early in gestation. They help neurons move, specialize, form connections, and get covered with myelin for faster signaling. A developing fetus relies on maternal thyroid hormone (before its own thyroid is fully functional).

Research has also shown that deficits in thyroid hormone (or changes in timing) can disrupt these processes, potentially leading to structural or functional brain differences that show up as ADHD, ASD, or other neurodevelopmental disorders.

Specifically, it’s thought that low thyroid hormone during early brain development can cause underdevelopment of the brain regions most crucial for attention, thinking, and social skills. Thyroid hormones also help control genes needed for synapse formation, brain plasticity, and overall brain wiring.

Studies show that maternal hypothyroidism is a risk factor for ADHD and ASD in offspring. Here are some of the relevant studies:

• A 2025 retrospective study of around 51,000 births reported that both hypo- and hyperthyroidism in mothers increased the risk of ASD, with longer duration across trimesters correlating with higher risk.

• The Norwegian Mother, Father and Child Cohort Study (MoBa), published in 2022, found that both high and low maternal thyroid hormone levels—even within normal ranges—were linked to ADHD risk.
• A Danish case-cohort study published in 2017 showed that overt hypothyroidism was associated with ASD, while isolated low free T4 was associated with both ASD and ADHD.
• A large study showed that maternal hypothyroidism is linked to an increased risk of attention-deficit/hyperactivity disorder (ADHD) in children. This risk is especially pronounced when hypothyroidism occurs before or during pregnancy, in the first trimester, or when there is a premature birth. 

• A meta‐analysis of 29 studies published in 2020 found that maternal hypothyroidism is associated with increased risk of ADHD and ASD in offspring.

• A 2018 retrospective analysis of around 250,000 children studied by Kaiser Permanente in California found that maternal hypothyroidism (diagnosed before or during pregnancy) increased the risk of ADHD in offspring.

• According to the American Thyroid Association, some studies of maternal thyroid hormone insufficiency (e.g., low free T4 or mild hypothyroidism) in early pregnancy show associations with ASD risk.

Not all studies agree on how strongly maternal hypothyroidism directly increases ADHD or ASD risk. Several factors make the picture more complicated:

• Timing: Thyroid levels in the first trimester are most important, but many studies measure later in pregnancy or after birth.
• Severity: Overt hypothyroidism poses a higher risk than mild or subclinical cases.
• Treatment: Women diagnosed early and treated with levothyroxine often have children with normal development.
• Other influences: Genetics, environmental exposures, and other maternal health conditions can all affect risk.

Despite these complexities, maternal hypothyroidism is widely recognized as a modifiable risk factor for neurodevelopmental disorders, highlighting the importance of early detection and care.

When a mother has low thyroid hormone levels during pregnancy (hypothyroidism), it can affect the baby’s brain development—especially in the first trimester, when the fetus is entirely dependent on the mother’s thyroid hormones. The risks are different, however, depending on whether the hypothyroidism is treated or untreated.

For untreated maternal hypothyroidism:

• Autism risk: Large cohort studies show children of mothers with untreated hypothyroidism have a 30 to 60% higher risk of ASD compared with children of euthyroid mothers. This risk is most significant when hypothyroidism occurs early in pregnancy.

• ADHD risk: Observational studies link untreated hypothyroidism to a 25 to 30% higher risk of ADHD.

For treated maternal hypothyroidism:

• Treatment: Standard care is thyroid hormone replacement with levothyroxine to normalize maternal thyroid hormone levels.

• Autism risk with treatment: When hypothyroidism is diagnosed and treated early, autism risk is reduced and often approaches baseline. Some studies still find a small increased risk (~10–20%) if diagnosis/treatment is delayed.

• ADHD risk with treatment: Treated cases show substantially reduced risk compared with untreated women, with increases closer to 10–15% above baseline.

• Timing matters: The most protective factor is starting treatment before or very early in pregnancy, since the first trimester is when maternal thyroid hormones are most critical for brain development.

Putting the risk in perspective

It’s important to compare relative risks (percent increases) with absolute risks (the actual chances of a child being diagnosed).

• Autism baseline risk: Around 2.8% of U.S. children (about 1 in 36).

• Untreated hypothyroidism raises this to about 4 to 4.5%.

• Treated hypothyroidism is closer to 3 to 3.5%.

• ADHD baseline risk: Around 9 to 10% of U.S. children (about 1 in 10).

• Untreated hypothyroidism raises this to about 11 to 13%.

• Treated hypothyroidism is closer to 10 to 11%.

All in all, maternal hypothyroidism does raise the risk of autism and ADHD in children, but the increase is usually modest in absolute terms (a few percentage points). The most significant risks are when hypothyroidism is undiagnosed or untreated early in pregnancy. With early detection and proper treatment, risks can be brought close to baseline.

Leading medical organizations, including the American Thyroid Association, recommend:

• Monitoring thyroid function during pregnancy is particularly important for women with symptoms, a family history, or risk factors for thyroid disease.

• Treatment with levothyroxine for women with overt hypothyroidism is essential for normal pregnancy and fetal development.

• Early intervention—ideally maternal levothyroxine treatment during the first trimester—gives the best chance to protect the baby’s brain development.

• The benefit of screening and treating subclinical hypothyroidism (TSH above reference range but below the threshold for overt hypothyroidism) remains an area of active research.

Treating hypothyroidism in pregnant women is essential for both maternal health and fetal brain development. The standard treatment is levothyroxine, a synthetic form of the thyroid hormone thyroxine (T4), which helps normalize hormone levels and supports proper neurological growth in the developing fetus. Early treatment—ideally before conception or during the first trimester—is crucial, as the fetus relies entirely on maternal thyroid hormones during this period. Treatment should be carefully monitored through regular blood tests to keep TSH and free T4 within the recommended pregnancy range, ensuring adequate dosing throughout gestation.

Treating hypothyroidism in pregnant women offers a wide range of benefits for both mother and baby. Proper management with levothyroxine not only normalizes thyroid hormone levels but also supports healthy fetal brain development, including neuron growth, synapse formation, and myelination, which are critical for cognitive function, attention, and social skills. Early and consistent treatment reduces the risk of neurodevelopmental disorders in children, such as ADHD and autism, and can prevent complications like preterm birth, low birth weight, and miscarriage. For the mother, treatment helps alleviate common hypothyroid symptoms—fatigue, weight gain, mood changes, and cold intolerance—improving overall energy and well-being during pregnancy. By maintaining thyroid hormone balance throughout gestation, women can optimize their own health while giving their child the best possible start.

For those planning a pregnancy or already expecting, emerging research on thyroid health highlights several important considerations:

• Early screening is key. If you are planning a pregnancy or are in the early stages, talk with your healthcare provider about thyroid function testing as soon as possible. Early knowledge allows for timely management if any issues are present.
• Prepare for pregnancy pre-conception. Optimize your thyroid levels – following guidelines for thyroid-stimulating hormone (TSH) levels during pregnancy – if you have a history of hypothyroidism. Ensuring that your thyroid hormone levels are within the normal range before conception—and maintaining them throughout pregnancy—is essential for your health and your baby’s development.
• Pay attention to symptoms. Common signs of hypothyroidism and thyroid dysfunction, such as fatigue, unexplained weight gain, dry skin, hair loss, and feeling unusually sensitive to cold, should never be ignored. Prompt evaluation can prevent complications.
• Timing matters. Research shows that early detection and treatment—ideally before conception or during the first trimester—of maternal thyroid dysfunction offer the best protection for your child’s development.
• Adequate treatment is more than taking medication. “Adequately treated” means keeping your TSH and free T4 within the normal range throughout pregnancy, typically with levothyroxine treatment. Inadequate control, even if medicated, can still carry some risk.

Most of the current evidence is from observational or retrospective studies. These are strong for associations but weaker for proving causality and measuring the impact of interventions (e.g., when treatment occurs, how “treatment” is defined, etc.).

In addition, few randomized controlled trials (RCTs) are available, especially ones that track long-term ADHD/ASD outcomes or begin early in pregnancy.

Timing is also underexplored. Many studies measure thyroid levels in the second trimester or later; fewer have very early first-trimester or pre-conception data and then follow long-term. Duration of exposure (how many trimesters) is emerging as an essential factor.

Finally, the effect of treatment is also unclear: does earlier diagnosis and tighter control (normalization of thyroid function) significantly reduce the risk of ADHD/ASD? Some studies suggest yes (or at least mitigate risk), others find the effect is limited. More trials would help clarify the situation.

Several new studies are underway to clarify further:

• The long-term neuropsychological outcomes in children exposed to treated versus untreated maternal hypothyroidism.

• The dose-response relationship between TSH/FT4 levels at different gestational windows and risk of ADHD or ASD.

• The interplay of genetic susceptibility and thyroid hormone action in neurodevelopment.

• More nuanced definitions and guidelines for what constitutes adequate treatment in subclinical disease.

Scientific evidence links maternal hypothyroidism to an increased risk of neurodevelopmental disorders in children, including ADHD and ASD. While the individual risk for any given child remains relatively low, timely detection and effective management of hypothyroidism is a proven, evidence-based strategy to support optimal fetal neurodevelopment. For women who are hypothyroid or planning pregnancy, Paloma offers convenient home thyroid test kits and virtual visits with healthcare providers, making it easier than ever to monitor hormone levels and adjust treatment as needed. These tools help ensure both maternal well-being and the healthiest possible start for their children. Open dialogue with providers, supported by Paloma’s at-home testing and virtual care, empowers women to manage thyroid function before and during pregnancy proactively.

• Maternal hypothyroidism during early pregnancy is a proven risk factor for ADHD and autism in children.
• The risk appears to be higher when hypothyroidism goes untreated for all or part of the pregnancy.
• The fetus depends entirely on maternal thyroid hormones in the first trimester for proper brain development.
• Up to 60% of women with thyroid disease are unaware of it, and routine prenatal care frequently does not test for a thyroid condition.
• Untreated hypothyroidism in a pregnant woman can raise autism risk for her child by 30–60% and ADHD risk by 25–30%.
• Early diagnosis and thyroid hormone replacement treatment can reduce these risks close to baseline.
• Home thyroid testing and virtual care make monitoring and managing thyroid health more convenient for expecting parents.