ESPE Abstracts

Background: Subtle impairments in the thyroid function of pregnant women are associated with poorer scores on mental developmental scales in their children at age 2–3 years, and with reduced performance in a simple reaction time test at 5–6 years. However, associations with school performance estimates have never been studied.

Objective and hypotheses: We aimed to assess the effect of normal variation in the maternal thyroid function during early pregnancy on school performance at age 5 years.

Method: This was a longitudinal study that included the data of 1196 healthy children from the Amsterdam Born Children and their Development study. Maternal serum free T₄ and TSH were obtained at a median pregnancy duration of 90 (interquartile range: 83–100) days. School performance was based on scores obtained in arithmetic and language tests from the nationwide monitoring and evaluation system. Poor school performance was defined as a test result <25th percentile and subnormal school performance as a test result <50th percentile. Multivariable logistic regression analysis was used and analyses were repeated after adjustment for family background and perinatal variables.

Results: Maternal hypothyroxinaemia (i.e., a maternal free T₄ in the lowest 10% of distribution) was associated with a 1.90 (95% CI: 1.26–2.87) –fold increased risk of subnormal performance in the arithmetic test (P=0.002). This relation persisted after statistical correction. Maternal hypothyroxinaemia was associated with a 1.79 (95% CI: 1.08–2.96) –fold increased risk of poor language performance (P=0.02) but statistical significance was lost after introduction of family background variables in the regression equation. No such relations were found with TSH.

Conclusion: Maternal hypothyroxinaemia at the end of the first trimester was associated with poorer performance in an arithmetic test, but not in a language test, in offspring at age 5 years.