Gowachirapant S, et al. - The effect of iodine supplementation was evaluated in mildly iodine-deficient pregnant women on neurodevelopment of their offspring in areas where schoolchildren were iodine sufficient. Among mildly iodine-deficient pregnant women, daily iodine supplementation had no effect on child neurodevelopment at age 5–6 years.

• The researchers randomly assigned (1:1) pregnant women in Bangalore, India, and Bangkok, Thailand to receive 200 μg iodine orally once a day or placebo until delivery, in this randomised, placebo-controlled trial.
• They performed randomisation with a computer-generated sequence and stratified by site.
• Verbal and performance IQ scores on the Wechsler Preschool and Primary Scale of Intelligence Third Edition (WPPSI-III) and the global executive composite score from the Behaviour Rating Inventory of Executive Function-Preschool Version (BRIEF-P) were the co-primary outcomes in the children at age 5-6 years.
• The trial was double-blinded; some unmasking was undertaken at age 2 years for an interim analysis, but participants and nearly all investigators remained masked to group assignment until age 5–6 years.
• Using mixed-effects models, data analysis was performed by intention to treat.

• At a mean gestational age of 10·7 weeks (SD 2·7), 832 women entered the trial between Nov 18, 2008, and March 12, 2011.
• Median urinary iodine concentration was 131 μg/L (IQR 81-213).
• Evaluated by monthly tablet counts, mean compliance with supplementation was 87%.
• The researchers analyzed 313 children (iodine group, n=159; placebo group, n=154) for verbal and performance IQ with WPPSI-III and 315 (iodine group, n=159; placebo group, n=156) for overall executive function with BRIEF-P.
• In the iodine group, mean WPPSI-III scores for verbal IQ were 89·5 (SD 9·8) and 90·2 (9·8) were noted in the placebo group (difference -0·7, 95% CI -2·9 to 1·5; p=0·77), and for performance IQ were 97·5 (12·5) in the iodine group and 99·1 (13·4) in the placebo group (difference -1·6, -4·5 to 1·3; p=0·44).
• The mean BRIEF-P global executive composite score in the iodine group was 90·6 (26·2) and 91·5 (27·0) in the placebo group (difference -0·9, -6·8 to 5·0; p=0·74).
• During gestation or at delivery, the frequency of adverse events did not differ between groups: 24 women in the iodine group and 28 in the placebo group reported adverse events (iodine group: abortion, n=20; blighted ovum, and n=2; intrauterine death, n=2; placebo group: abortion, n=22; blighted ovum, n=1; intrauterine death, n=2; early neonatal death, n=1; and neonatal death, n=2).