Inter-relationship between evolutions of the temporal trend of urinary iodine excretion with iodized salt accessibility and thyroid function in an exclusive cohort of mothers residing in a mild iodine-deficient region

Maternal iodine deficiency (UIC<150 µg/L) is common in regions with borderline iodine sufficiency. Hence, exploring evolution of the temporal trend for UIC during pregnancy as well as impact of possible modifiers aids in defining the timing and the dose of iodide administration supplement during foetal development. The aim of present investigation was to evaluate the inter-relationships between UIC and iodized salt accessibility and thyroid function as assessed by thyroid-stimulating hormone (TSH) in an exclusive cohort of pregnant women depending on household salt as the predominant source of iodine intake.

Healthy pregnant women (n=95; gestation > 4 and < 8 weeks) and non-pregnant women (n=40) with similar lifestyle and dietary habits were enrolled. UIC, TSH and table-salt iodine content were determined.

Median UIC (µg/L) according to trimesters was significantly lower than that of controls (61.6, 130.2 and 90.3 vs 133.8). Accordingly, prevalence of subjects with UIC<150 µg/L were 97.9, 67.4, 77.9 and 60. Median TSH (mIU/L) according to trimesters and control group were 1, 1.6, 1.4 and 1.6. Accordingly, prevalence of subjects with abnormal lower TSH limit was 17.2, 8.5, 3.2 and 2.4.

This investigation demonstrates that UIC varies according to the foetal life cycle and that the highest frequencies of severe iodine (UIC <50 μg/L) were identified at the first- and third trimesters. This investigation paves the way for future studies aiming at exploring the therapeutic impact of iodine supplementation on body iodine stores during pregnancy.