The prevalence of thyroid dysfunction in this national Belgian pregnancy cohort was surprisingly high, with 7.2% having elevated serum TSH values. This was likely due, at least in part, to mild iodine deficiency. The first-trimester median urinary iodine concentration was 117 mcg/L, below the range of 150 mcg/L to 249 mcg/L considered adequate in pregnant populations.

“Thyroid dysfunction and mild iodine deficiency during pregnancy are associated with poor obstetric outcome, and therefore correction of iodine deficiency early in pregnancy is unanimously recommended,” Rodrigo Moreno-Reyes, MD, Erasme Hospital Université Libre de Bruxelles in Belgium, and colleagues wrote.