Scientists warn persistent thyroid imbalance during pregnancy raises autism risk

Two large studies suggest that untreated or persistent maternal thyroid imbalance during pregnancy is linked to higher autism risk in children, underscoring the importance of monitoring thyroid health in expectant mothers.

As more children are diagnosed with autism, many people continue to ask what causes it.

Autism, also known as autism spectrum disorder (ASD), affects how a person communicates, interacts with others and behaves, often involving repetitive actions or particular interests. Research indicates that a wide range of factors may contribute to autism.

A recent study suggests that untreated thyroid hormone imbalance during pregnancy may increase the likelihood of a child developing autism.

Thyroid dysfunction — a condition in which the thyroid gland produces either too little or too much hormone — may raise the chances of giving birth to a child with autism.

Thyroid hormone imbalance in pregnancy occurs when a woman’s thyroid gland does not produce the correct levels of hormones (T3 and T4). These hormones are essential because they support the mother’s metabolism and the baby’s growth and brain development.

When thyroid hormone levels are too low (hypothyroidism) or too high (hyperthyroidism) during pregnancy, complications may arise, including miscarriage, preterm birth, low birth weight and developmental challenges for the baby.

Untreated hypothyroidism, in particular, has been linked in some studies to neurodevelopmental conditions in children, including an increased risk of autism.

Subtle symptoms

Because symptoms of thyroid imbalance can be subtle — such as fatigue, weight changes, mood swings or changes in heart rate — many cases may go unnoticed without routine blood tests.

The recent study found that the longer a mother’s thyroid problems continued, the higher the child’s risk became. For example, children born to mothers with low thyroid hormone levels throughout all three trimesters had more than three times the likelihood of being diagnosed with autism. However, when thyroid imbalances were effectively managed during pregnancy, the increased risk was not significant.

The study, published in The Journal of Clinical Endocrinology & Metabolism, examined more than 51,000 singleton pregnancies between 2011 and 2017 and tracked the children’s health until 2021.

Researchers focused on how thyroid hormone levels changed over time during pregnancy and whether prolonged imbalance increased the chance of a child later being diagnosed with autism.

According to the findings, around 8.6 per cent of the mothers had some type of thyroid hormone abnormality either before or during pregnancy. When a woman already had a diagnosed thyroid condition before conception — meaning it was typically monitored and treated — the researchers found no significant rise in autism risk for her child.

Abnormal thyroid hormone levels

However, the situation differed when thyroid hormone levels remained abnormal during pregnancy. When pre-existing thyroid dysfunction continued into pregnancy, or when thyroid imbalance persisted across multiple trimesters, the risk of autism increased considerably. In these cases, the adjusted hazard ratio reached 2.61, indicating more than double the risk compared with pregnancies in which thyroid levels stayed normal.