BACKGROUND
Thyroid hormone plays an important role in the development of the baby during pregnancy, including brain development. The baby’s own thyroid gland does not start making enough thyroid hormone until about 4–5 months of pregnancy. Therefore, thyroid hormone needed during the critical period of development in early pregnancy comes from mothers’ thyroid hormone crossing the placenta to baby. Abnormal thyroid function, especially low thyroid hormone levels (hypothyroidism) in mothers during pregnancy have been associated with poor development in children, such as lower IQ.

Autism spectrum disorder is a complex condition that is likely affected by many different factors, including genetic and environmental factors. With its important role in brain development, thyroid function has been of interest as one of the potential factors that contribute to the risk of autism spectrum disorder in children. However, studies have not yet shown a clear link between hypothyroidism in mothers during pregnancy and children’s diagnosis of autism spectrum disorder. The current study investigated possible association between abnormal thyroid function in mothers during pregnancy and children’s risk of developing autism spectrum disorder.

THE FULL ARTICLE TITLE
Elbedour L et al. Maternal thyroid hormone imbalance and risk of autism spectrum disorder. J Clin Endocrinol Metab. Epub 2025 Nov 25:dgaf596; doi: 10.1210/clinem/ dgaf596. PMID: 41288361

SUMMARY OF THE STUDY
This study included 51,296 pregnant women seen in one hospital in Israel from 2011-2017, of whom 8.6% (4,409 women) had abnormal thyroid function. Participants had at least one thyroid hormone level measurement during pregnancy. Women who had hypothyroidism (low thyroid hormone levels) and hyperthyroidism (high thyroid hormone levels) diagnosed before pregnancy were categorized as having “chronic thyroid dysfunction.” Women who had any abnormal thyroid hormone levels during pregnancy were categorized as having “gestational thyroid dysfunction.” Diagnosis of autism spectrum disorder in children born to these women was assessed from a national database.

There was no significant difference in the number of children diagnosed with autism spectrum disorder between those of mothers with normal thyroid function and those of mothers with either chronic or gestational thyroid dysfunction. However, if women had both chronic and gestational thyroid dysfunction, especially hypothyroidism, their children had about 2.7-fold higher risk of autism spectrum diagnosis compared to children of women without thyroid dysfunction. In contrast, children of women who had chronic thyroid dysfunction but had normal thyroid hormone levels throughout pregnancy did not have a higher risk of autism spectrum disorder compared to children of women with normal thyroid function. Similarly, children of women who only had gestational thyroid dysfunction, but not chronic thyroid dysfunction, did not have a higher risk of autism spectrum disorder compared to children of women with normal thyroid function. In addition, having persistently low thyroid hormone levels during pregnancy in more than one trimester was associated with an increased risk of developing autism spectrum disorder in children.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The authors concluded that inadequately treated hypothyroidism, as in cases of hypothyroidism in the mother diagnosed before pregnancy with abnormal thyroid hormone levels during pregnancy, may be associated with increased risk of autism spectrum disorder in children. If hypothyroidism in the mother diagnosed before pregnancy was well-controlled during pregnancy, risk of autism spectrum disorder in children was not increased. The longer maternal hypothyroidism remains inadequately controlled during pregnancy, the higher the risk of autism spectrum disorder in children. The findings of this study suggest that appropriate levothyroxine treatment of hypothyroidism in the mother to maintain normal thyroid hormone levels during pregnancy would be able to decrease or eliminate potential risk of autism spectrum disorder in children with hypothyroid mothers.

— Sun Y. Lee, MD, MSc

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