Thyroid Imbalance During Pregnancy Increases Autism Risk in Offspring — Evidence Review

Women with persistent thyroid hormone irregularities during pregnancy face an increased risk of having a child diagnosed with autism, according to a large new study; this finding is largely consistent with prior research, which also links maternal thyroid dysfunction to higher autism risk. Related studies broadly agree that maternal thyroid imbalance, especially when untreated or spanning multiple trimesters, is associated with greater likelihood of neurodevelopmental disorders such as autism, as summarized in the Journal of Clinical Endocrinology & Metabolism.

• Several studies have found that both overt and subclinical maternal thyroid dysfunction (including hypothyroidism and hyperthyroidism) is associated with increased risk of autism and other neurodevelopmental disorders in offspring, particularly when abnormalities are present early or throughout pregnancy 3 4 7.
• The relationship between the timing, duration, and treatment of maternal thyroid dysfunction and autism risk is nuanced: while some studies report that treated thyroid dysfunction does not increase risk, ongoing hormone imbalance across multiple trimesters—especially if untreated—raises autism risk, echoing the new study’s findings 3 7.
• Biomarker-based research supports a link between maternal thyroid autoantibodies and autism risk, strengthening the biological plausibility of these associations, though some studies suggest mild iodine deficiency or isolated neonatal thyroid hormone levels may not independently drive autism risk 1 5 8.

Study Overview and Key Findings

Maternal thyroid hormones are essential for fetal brain development, and disruptions during pregnancy have been previously linked to neurodevelopmental disorders. This new study is significant in that it investigates not only the presence of thyroid hormone irregularities, but also their persistence across multiple trimesters, and examines whether adequate treatment mitigates risk. The study draws from an extensive birth cohort, providing a robust population-level perspective on how chronic, untreated thyroid imbalance throughout pregnancy may influence the likelihood of autism in children—adding nuance to earlier research that focused more on early pregnancy or single time points.

Property	Value
Organization	Ben-Gurion University of the Negev, Meir Medical Center, Tel Aviv University, Soroka University Medical Center
Journal Name	The Journal of Clinical Endocrinology & Metabolism
Authors	Idan Menashe, Leena Elbedour, May Weinberg, Gal Meiri, Analya Michaelovski
Population	Women with thyroid hormone irregularities during pregnancy
Sample Size	n=51,000
Methods	Observational Study
Outcome	Risk of autism spectrum disorder in offspring
Results	Ongoing thyroid imbalance across trimesters increases autism risk.

Literature Review: Related Studies

To place these findings in context, we searched the Consensus paper database, which includes over 200 million research papers. The following search queries were used to identify relevant studies:

1. thyroid function pregnancy autism risk
2. trimesters thyroid imbalance autism correlation
3. simple thyroid check autism prevention

Below, we summarize the main themes and findings from related studies:

Topic	Key Findings
How does maternal thyroid dysfunction during pregnancy impact autism risk in offspring?	- Multiple studies report that maternal hypothyroidism or hyperthyroidism is associated with increased risk of autism spectrum disorder (ASD) in children 3 4 7. - Treatment of maternal thyroid dysfunction appears to reduce this risk, while untreated or multi-trimester imbalance increases risk 7.
What roles do timing and severity of thyroid hormone imbalance play?	- The risk for ASD is higher when thyroid hormone abnormalities are present across multiple trimesters or are severe (i.e., overt hypothyroidism or hyperthyroidism) 3 4 7. - Early pregnancy thyroid abnormalities, particularly low free T4, are linked to poorer cognitive outcomes and higher autistic traits 2 3.
Are specific biomarkers or nutritional factors (e.g., autoantibodies or iodine) important in mediating risk?	- Maternal thyroid peroxidase antibodies (TPO-Ab+), as a marker of autoimmune thyroiditis, are associated with increased risk of autism in offspring, even when hormone levels are normal 1. - Mild-to-moderate iodine deficiency in later pregnancy does not appear to independently increase ASD risk 8.
Do neonatal thyroid hormone levels predict autism risk?	- Neonatal T4 and TSH levels show weak or no significant associations with ASD overall, but the lowest T4 levels in certain subgroups may modestly increase risk 5 6.

How does maternal thyroid dysfunction during pregnancy impact autism risk in offspring?

A substantial body of research supports a link between maternal thyroid dysfunction and increased risk of ASD in children. The new study’s finding that ongoing and untreated thyroid hormone imbalance across pregnancy heightens autism risk is consistent with most prior observational and meta-analytic evidence, which demonstrates higher ASD rates among offspring of mothers with hypothyroidism or hyperthyroidism, particularly when not adequately treated 3 4 7.

• Both overt hypothyroidism and hyperthyroidism in mothers are associated with increased ASD risk in offspring 3 4 7.
• Treatment and normalization of thyroid hormone levels during pregnancy appear to mitigate this risk 7.
• Maternal thyroid dysfunction is linked not only to ASD but also to other neurodevelopmental outcomes (e.g., ADHD, epilepsy) 3 4.
• The consistency across large cohort and meta-analytic studies reinforces the biological plausibility of these associations 3 4 7.

What roles do timing and severity of thyroid hormone imbalance play?

The timing and persistence of maternal thyroid hormone abnormalities significantly affect neurodevelopmental outcomes. The new study, by evaluating multi-trimester imbalance, contributes important nuance, showing a dose-response relationship between the number of affected trimesters and autism risk—an observation supported by earlier studies focusing on early pregnancy thyroid function and the severity of dysfunction 2 3 7.

• Early pregnancy is a critical period for fetal brain development, and low maternal free T4 at this stage is linked to lower child IQ and higher autistic traits 2 3.
• The risk for ASD and other neurodevelopmental disorders increases with the number of trimesters affected by thyroid dysfunction 3.
• Severe or overt forms of thyroid dysfunction pose higher risks compared to milder or subclinical dysfunction 3 7.
• The findings suggest the importance of ongoing monitoring, not just a single early-pregnancy assessment 2 3 7.

Are specific biomarkers or nutritional factors (e.g., autoantibodies or iodine) important in mediating risk?

In addition to hormone levels, certain biomarkers such as thyroid peroxidase antibodies (TPO-Ab) have been linked to increased autism risk, suggesting an autoimmune component. However, mild-to-moderate iodine deficiency later in pregnancy does not appear to independently increase risk, indicating that not all thyroid-related factors equally influence neurodevelopmental outcomes 1 8.

• TPO-Ab positivity in maternal serum is associated with a significantly higher risk of autism in offspring, even when thyroid hormone levels are otherwise normal 1.
• Maternal autoimmune thyroiditis may be an independent risk factor for ASD 1.
• Mild iodine deficiency in mid-to-late gestation was not independently associated with ASD risk 8.
• The new study did not specifically address autoimmunity or nutritional factors, indicating a need for further integrated research 1 8.

Do neonatal thyroid hormone levels predict autism risk?

Evidence regarding the predictive value of neonatal thyroid hormone levels for ASD is less consistent. While some studies note lower mean T4 levels in neonates with ASD, these associations often diminish after adjustment for confounders. The strongest risk signals are seen in specific subgroups with the lowest T4 levels, but overall, neonatal TSH and T4 are not robust predictors for ASD in the general population 5 6.

• No significant associations were found between overall neonatal TSH or T4 levels and ASD after adjusting for confounders 5 6.
• The lowest T4 percentile groups may have a modestly increased risk, especially when measured after 48 hours post-birth 5.
• Maternal—but not neonatal—TSH levels show an inverse association with ASD risk 6.
• These findings highlight that maternal thyroid status during pregnancy is likely a more important determinant of ASD risk than neonatal thyroid hormone levels 5 6.

Future Research Questions

While the current study advances understanding of the relationship between persistent maternal thyroid hormone imbalance and autism risk, several gaps and questions remain. Future research is needed to clarify mechanisms, refine risk stratification, and guide clinical interventions that could mitigate neurodevelopmental risks associated with thyroid dysfunction in pregnancy.

Research Question	Relevance
Does the type and timing of thyroid dysfunction (e.g. hypothyroidism vs. hyperthyroidism) differentially affect autism risk?	Clarifying whether risk varies by specific thyroid disorder and gestational window could inform targeted monitoring and intervention strategies 2 3 4 7.
Can early and continuous treatment of maternal thyroid dysfunction fully normalize autism risk in offspring?	Determining the effectiveness of intervention timing and adequacy would support evidence-based guidelines for thyroid monitoring and treatment during pregnancy 7.
What are the mechanisms by which maternal thyroid autoimmunity increases autism risk independent of hormone levels?	Understanding how thyroid autoantibodies contribute to neurodevelopmental outcomes could reveal new prevention or treatment targets 1.
Do genetic or environmental factors modify the association between maternal thyroid dysfunction and autism risk?	Identifying modifiers such as race/ethnicity, nutritional status, or family history may help personalize risk assessments and interventions 7 8.
Is routine thyroid screening and adjustment of treatment throughout pregnancy cost-effective and clinically beneficial for autism prevention?	Research on the benefits, risks, and costs of frequent thyroid monitoring and therapy adjustment can inform clinical guidelines and public health policy 4 7.