PerspectiveIn the Journals

Maternal thyroid dysfunction may lead to poor school performance in adolescents

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November 10, 2015

Adolescents whose mothers had thyroid dysfunction during early pregnancy are likely to have poor scholastic performance, according to recent study findings published in Thyroid.

Further, the adolescents own thyroid dysfunction also is associated with difficulties in school performance assessed by self-evaluation, according to the researchers.

Fanni Päkkilä, MD, of Oulu University Hospital in Finland, and colleagues evaluated data from the Northern Finland Birth Cohort 1986 on 5,791 women whose maternal serum samples were obtained during early pregnancy and serum samples from their children at age 16 years (n = 5,829). Researchers sought to determine the effect of maternal thyroid dysfunction on children’s school performance, as well as the child’s own thyroid dysfunction.

Participants’ school performances were evaluated by the main teacher when the child was aged 8 years and again by themselves when they were aged 16 years.

Writing difficulties were the most common problem at age 8 years (16.5%), followed by reading difficulties (11.6%) and difficulties with mathematics (8.2%); 20.9% had difficulties in at least one of those. Scholastic problems at age 8 years did not differ significantly between children of mothers with thyroid dysfunction and those without.

During the self-assessed evaluation at age 16 years, most participants reported being worse than average in Finnish or math (27.7%), followed by being worse than average in math (23.4%), being worse than average in the Finnish language (8.6%) and repeating a class (1.8%). Similar outcomes were found among participants of mothers with hypothyroidism and those with euthyroidism.

Participants of mothers with subclinical hypothyroidism had higher odds of having difficulties in math (OR = 1.4; 95% CI, 0.95-2.08) compared with those of mothers with overt hypothyroidism. Compared with participants of mothers with euthyroidism, participants of mothers with subclinical hypothyroidism were more likely to have repeated a class (OR = 2.14; 95% CI, 1.01-4.53).

Compared with participants of mothers with euthyroidism, participants of mothers with hypothyroidism were more likely to have self-reported difficulties in math (OR = 1.56; 95% CI, 1.03-2.38).

Participants of mothers who were hypothyroxinemic were more likely to have repeated a class compared with participants of mothers with euthyroidism (OR = 3.49; 95% CI, 1.06-11.48); all of these participants were boys.

Prevalence and odds of a participant having severe intellectual difficulty of mild cognitive limitation were not related to maternal thyroid dysfunction.

More difficulties in the Finnish language were found among girls (OR = 2.82; 95% CI, 1.42-5.61) with thyroid dysfunction compared with those with euthyroidism. Self-reported difficulties in Finnish and/or mathematics were more often self-reported among boys with hypothyroxinemic test results compared with those with euthyroidism (OR = 2.13; 95% CI, 1.26-3.62).

“In conclusion, abnormal maternal thyroid function status during early pregnancy increased adolescents’ odds of repeating a class at school and had also some effect on the adolescents’ performance in Finnish language and mathematics at age 16,” the researchers wrote. “It did not, however, increase a child’s odds of having an intellectual problem. Additionally, adolescents’ own abnormal thyroid function status had some effect on their self-evaluated school performance.” – by Amber Cox

Disclosure: The researchers report no relevant financial disclosures.

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PERSPECTIVE
Tim Korevaar

Tim Korevaar

The paper by Päkkilä and colleagues investigates the hypothesis that abnormal levels of maternal thyroid hormones during early pregnancy have an adverse effect on fetal brain development. This is a well-established hypothesis, and earlier clinical studies have shown that abnormal maternal thyroid hormone levels during pregnancy are associated with slower reaction times, lower IQ and lower cerebral gray matter volume in the offspring.

This study is particularly interesting because even though school performance is tightly linked to the previously mentioned outcomes, it is a real-life outcome. However, two factors are crucial for the interpretation of such data: First of all, the effects shown for IQ are rather small (2 to 4 points in papers using a similar approach), and although such small changes can have a large impact on a population as a whole, it is unlikely to result in large differences in school performance. Second, school performance is an outcome with even more measurement error than IQ testing, as it can be distorted by more socioeconomic factors. Fortunately, the large number of participants in the study can potentially overcome such uncertainties (particularly when thyroid-stimulating hormone and free thyroxine are analyzed continuously).Back to the results of the study; hyperthyroidism of the mother was associated with difficulties in mathematics and with Finnish in girls while hypothyroxinemia was associated with repeating a class in boys. Because many statistical tests were performed (64 not counting child sex stratifications) and there is very little consistency in the rest of the analyses, it is hard to interpret the results. The associations with both low and high thyroid function in this study, combined with a previous study from the Netherlands (Noten AM, et al. Euro J Endocrinol. 2015;doi:10.1530/EJE-15-0397) showing that maternal hypothyroxinemia is associated with lower arithmetic performance, do suggest that both low and high maternal thyroid function during early pregnancy are associated with adverse brain developmental outcomes. As children from mothers that participated in studies during pregnancy are getting older, I look forward to more papers on school performance outcomes that can give us a better insight into lifetime effects of differences in early pregnancy maternal thyroid hormone levels.


Tim Korevaar, MD, MSc
Erasmus University Medical Center in Rotterdam, Netherlands

Disclosure: Korevaar reports no relevant financial disclosures.