578 Associations between maternal thyroid function in pregnancy & child neurodevelopmental outcomes at 20 months in the seychelles child development study NC2

Background Maternal thyroid hormones facilitate optimal foetal neurodevelopment, however the exact role of the thyroid hormones on specific cognitive outcomes is unknown. Objectives This study aimed to investigate associations between maternal thyroid function and neurodevelopmental outcomes at 20 months in the Seychelles Child Development Study (SCDS, n=1535). Methods Maternal free thyroid hormones (fT3, fT4 and fTSH) were assessed at 28 weeks gestation with a range of child cognitive outcomes analysed at 20 months. Dietary iodine intake was analysed for a subset of women through a Food Frequency Questionnaire (FFQ) (n=422), with a median iodine intake of 233µg/d, slightly below the recommended iodine intake for pregnancy as advised by the WHO (>250µg/d). Linear regression analysis was used to test associations between serum concentrations of fT3, fT4 and fTSH and child cognitive outcomes. Thyroid hormones were analysed both as continuous data and also categorised as quintiles. 95% of mothers had optimal thyroid function based on their TSH concentrations. Results Results show that maternal fT3, fT4 and TSH were not significantly associated with any cognitive outcomes at 20 months in this high fish-eating population. However, a positive association, using quintiles for fT3, was reported for Motor Development Index (MDI; a subtest of the Bayley’s Scales of Infant Development), between Q3 vs Q4 (β 0.073; p 0.043) and for Q3 vs Q5 (β value 0.086; p 0.018). Conclusions Thus, it is possible mothers in our cohort, who largely have optimal thyroid function and iodine intakes, are able to regulate thyroid function throughout pregnancy to meet neurodevelopmental needs. However, it is likely that minor imbalances of fT3, as indicated from our quintile analysis, may impact offspring neurodevelopment. Thus, further investigation is warranted, particularly focusing on thyroid hormone fluctuation throughout pregnancy in relation to possible associations with infant neurodevelopment.