The effect of iodine supplementation in pregnancy on early childhood neurodevelopment and clinical outcomes: results of an aborted randomised placebo-controlled trial

Aborted randomised placebo-controlled trial in pregnant women with singleton pregnancies enrolled before 20 weeks' gestation in Australia and New Zealand. Participants were not taking iodine-containing supplements and had no known thyroid disease or major fetal abnormalities.

Pregnant participants received 150 μg iodine as potassium iodide, taken orally as one tablet daily from randomisation until the end of pregnancy, compared with placebo. Mean exposure before unblinding was 16 weeks (range 2-23 weeks).

Iodine supplementation during pregnancy did not improve early childhood neurodevelopment and did not change the other clinical outcomes assessed. At 18 months, Bayley-III scores were similar for cognitive performance (99.4 vs 101.7; MD -2.3, 95% CI -7.8 to 3.2; P = 0.42), language (97.2 vs 97.9; MD -0.7, 95% CI -7.0 to 5.6; P = 0.83), and motor function (93.9 vs 92.4; MD 1.4, 95% CI -4.0 to 6.9; P = 0.61). Although iodine status improved in the active group, there were no between-group differences in breast milk iodine concentration, cord thyroid measures, birth weight, birth length, head circumference, placental weight, NICU admission, or neonatal death. The authors concluded that adequately powered trials are needed for conclusive evidence.

The trial was small and aborted early, leaving it underpowered for clinical and neurodevelopmental outcomes. Follow-up was limited to early childhood, and some outcome data were unavailable or only partially reported, reducing precision and generalizability.