A large retrospective cohort study has examined whether thyroid hormone imbalance during pregnancy is associated with autism spectrum disorder (ASD) in offspring, offering new data relevant to prenatal testing and monitoring. The study, published in the Journal of Clinical Endocrinology & Metabolism, analyzed 51,296 single-baby births at Soroka University Medical Center, Israel, from 2011 to 2017, with follow-up through 2021.
Maternal thyroid status was determined using electronic health records and trimester-specific thyroid function tests, including TSH and free T4, performed by electrochemiluminescence immunoassay. About 8.6 percent of mothers showed abnormal thyroid function, classified as chronic hypothyroidism, gestational hypothyroidism, hyperthyroidism, or combinations of these conditions.
Overall, the researchers found no significant difference in ASD incidence between children born to mothers with normal thyroid function and those with any form of thyroid dysfunction (log-rank P = .27). However, more detailed analysis identified a specific subgroup at increased risk. Children born to mothers with both chronic and gestational hypothyroidism showed a significantly higher cumulative incidence of ASD compared with those born to mothers with normal thyroid funtion. Chronic hypothyroidism alone – likely reflecting adequate treatment – was not associated with higher ASD risk.
A dose–response pattern emerged in trimester analyses. The longer gestational hypothyroidism persisted, the higher the associated ASD risk. Exposure during one trimester produced an adjusted hazard ratio of 1.69, rising to 2.39 for exposure across two trimesters and 3.25 when hypothyroidism was present in all three trimesters. Similar patterns appeared in women who had both chronic and gestational hypothyroidism. Cumulative incidence curves showed steeper ASD incidence trajectories among children whose mothers had persistent thyroid imbalance.
Hyperthyroidism could not be assessed in depth because of small sample sizes. Among children diagnosed with ASD, symptom severity did not differ meaningfully across thyroid-exposure groups, aside from slightly higher scores in those exposed to both chronic and gestational dysfunction.
The findings reinforce the role of maternal thyroid testing as a key component of prenatal screening. Because fetal neurodevelopment depends on maternal thyroid hormones – especially early in pregnancy – consistent measurement and timely correction of thyroid abnormalities may help mitigate potential neurodevelopmental risks. The study also suggests that well-managed chronic hypothyroidism is not associated with increased ASD risk, highlighting the importance of effective treatment and monitoring throughout gestation.
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