A related commentary highlights that it is well known that severe iodine deficiency during pregnancy affects foetal brain development and has implications for cognition in later life, however the effects of mild-to-moderate deficiency during pregnancy are less well known. The results of this study should however be interpreted with caution, firstly, the pregnant women recruited in India were actually iodine sufficient, whereas those recruited in Thailand were iodine deficient. Also, a major limitation of all iodine research is the absence of a method to assess individual iodine status, hence measures of group status are currently used to classify pregnant women. This approach is needed because urinary iodine concentration, although useful at the population level, cannot be used for individuals as a result of high intra-individual variability. Future trials would benefit from a method to determine, at recruitment, whether individual women were iodine deficient, and therefore whether iodine supplementation would be appropriate.
In view of these facts, although the trial provides useful information, it cannot be considered as conclusive evidence that iodine supplementation has no benefit in mildly-to-moderately deficient pregnant women in terms of offspring neurodevelopment
A separate article discusses ways to improve the clinical impact of randomised trials in thyroidology