SickKids study finds hypothyroidism in pregnant women may reduce cognitive abilities in children

A new study led by The Hospital for Sick Children (SickKids) shows that children born to women treated for hypothyroidism during pregnancy may be at risk for reduced cognitive abilities and behaviour problems, if mother’s treatment was not properly adjusted during pregnancy.

Hypothyroidism is a condition where the body lacks sufficient thyroid hormone. Approximately two to three per cent of pregnant women experience hypothyroidism without any symptoms and are not even aware that their thyroid levels are low. This hormone is essential for fetal brain development and is especially critical in early pregnancy, before the fetal thyroid system starts to function. During this early stage the maternal hormone is the primary source for the baby’s developing brain.

“Our findings demonstrate how critical it is for pregnant women to have their thyroid hormone levels checked and monitored throughout pregnancy to ensure normal brain development in their children,” says Dr. Joanne Rovet, principal investigator on the study, and Senior Scientist in Neurosciences & Mental Health at SickKids.

The study found that children whose mothers were inadequately treated for hypothyroidism had selective memory problems including learning new things and remembering past events, as well as issues with attention and behaviour.

The research team compared children aged 10 to 12 years old born to women with inadequately treated hypothyroidism during pregnancy to a control group of children from women with normal thyroid function. The researchers followed these groups of children since birth and all children received structural and functional MRIs and did cognitive testing with an emphasis on memory.

The study focused on an area of the brain called the corpus callosum, because it starts to develop very early in gestation and serves to connect the right- and left- brain hemispheres. Recent evidence has shown abnormalities in this part of the brain in children with autism and ADHD, which are both associated with maternal hypothyroidism. This study found that compared with controls, those born to hypothyroid women had a smaller front and larger back portion of the corpus callosum and these effects reflected the number of trimesters the mother was hypothyroid and also predicted executive function and verbal comprehension skills in the child.

The study is published online in Thyroid and was supported by Canadian Institute of Health Research (CIHR).