Abstract
Adequate iodine intake during pregnancy is essential to maintain optimal maternal thyroid function which is crucial for fetal neurodevelopment. Though, globally, iodine deficiency is considered to be the single, most important, preventable cause of brain damage, many pregnant women are still iodine-deficient. The research work presented in this thesis aimed to investigate several aspects of maternal iodine nutrition, including: (i) the determinants of iodine status in pregnancy; ii) the effect of advancing gestation on urinary-iodine concentration which is the most commonly-used biomarker of population iodine-status; iii) the usefulness of serum thyroglobulin as a functional biomarker of longer-term iodine nutrition in pregnancy; iv) the effect of maternal iodine deficiency in pregnancy, as measured in multiple spot-urine samples, on child cognition; v) the effect of iodine supplementation of mildly-to-moderately iodine-deficient pregnant women on thyroid function and child cognition. In the first study, data from three European birth-cohorts were used. Milk and dairy products were found to be an important, common, dietary determinant of iodine status in pregnancy; cohort-specific determinants were also identified. In the second study, three spot-urine iodine measurements from each trimester were used in longitudinal analysis which showed an increase in urinary-iodine concentration across pregnancy. The third study showed that thyroglobulin was negatively associated with urinary-iodine concentration in an iodine-sufficient and a mildly iodine-deficient pregnant population; this suggested that thyroglobulin could be used as a complementary indicator of population iodine status. In the fourth study, iodine deficiency at multiple gestational time-points was associated with lower non-verbal intelligence quotient in children at 8 years. In the final study, evidence of the effects of iodine supplementation of mildly-to-moderately iodine-deficient pregnant women on thyroid function and child cognition was reviewed systematically; the results highlighted the lack of good-quality evidence from randomised-controlled trials to support recommendations for iodine supplementation in pregnancy in these areas. Public-health strategies aimed at educating pregnant women and women of childbearing age on the importance of iodine and the ways that they can meet iodine requirements through diet are needed. An accurate assessment of iodine status in pregnancy would be valuable for public-health monitoring and future research.