Opposite variations in maternal and neonatal thyroid function induced by iodine supplementation during pregnancy

Area of Science:

• Endocrinology
• Perinatal Medicine
• Nutritional Science

Background:

• Limited understanding of moderate maternal iodine intake effects on fetal thyroid function.
• Iodine deficiency is a global concern impacting maternal and infant health.
• Previous research focused on iodine deficiency extremes, not moderate variations.

Purpose of the Study:

• To investigate the impact of maternal iodine supplementation on maternal and fetal/neonatal thyroid function in a mild-to-moderate iodine-deficient population.
• To determine if maternal iodine intake influences thyroid-stimulating hormone (TSH) and thyroglobulin levels in pregnant women and their newborns.
• To assess the sensitivity of the fetal thyroid to iodine exposure.

Main Methods:

• Prospective study in Denmark involving pregnant women at term (n=144) and cord blood samples (n=139).
• Comparison between women taking iodine-containing supplements (150 µg/day) and those not taking supplements.
• Analysis of serum TSH and thyroglobulin levels in mothers and neonates.

Main Results:

• Maternal iodine supplementation was associated with a 7.6% decrease in maternal TSH (P < 0.05).
• Conversely, cord blood TSH was 27.3% higher in the supplemented group (P < 0.05).
• Inverse correlation between thyroglobulin and TSH in cord blood (P < 0.001) suggests high thyroglobulin indicates low iodine intake and high TSH.

Conclusions:

• Maternal iodine supplementation in mild iodine deficiency induces opposing effects on maternal and fetal thyroid function.
• The fetal thyroid demonstrates heightened sensitivity to the inhibitory effects of iodine, contrary to previous assumptions.
• Findings suggest careful consideration of iodine supplementation timing and dosage during pregnancy, especially in iodine-sufficient or mildly deficient regions.