Evaluating iodine deficiency in pregnant women and young infants. Complex physiology with a risk of misinterpretation

Objective: To review methods for evaluating iodine deficiency in pregnant women and Young infants and to discuss factors to be considered in the interpretation of their results. Design: Review of the literature regarding the various methods available for assessing iodine status. Setting: Population Surveys and research studies. Subjects: Pregnant women and young infants. Results. Several factors to consider when assessing iodine status in pregnant women and young infants include: 1) the urinary iodine (UI) concentration (mu g l(-1)) is not interchangeable with 24 h UI excretion (mu g per 24 h); 2) the concentration of iodine in a spot or casual urine sample cannot be used to diagnose iodine deficiency in an individual; 3) a moderate fall in the concentration of serum free T4 during pregnancy is not a sign of maternal iodine deficiency; 4) an increase in the concentration of serum thyroglobulin (Tg) during pregnancy is not a sign of maternal iodine deficiency; 5) a higher concentration of TSH and Tg in cord blood than in maternal blood is not a sign of iodine deficiency in the mother or neonate; and 6) thyroid function in a full-term foetus, a neonate or a small child is not more sensitive to a mild iodine deficiency than in the mother. Conclusions: if the iodine status Of pregnant women and small children is not to be Misjudged, the above six factors need to be taken into account.