Neonatal Thyroid-Stimulating Hormone Concentrations in Belgium: A Useful Indicator for Detecting Mild Iodine Deficiency?

Abstract

It has been proposed that neonatal thyroid-stimulating hormone (TSH) concentrations are a good indicator of iodine deficiency in the population. A frequency of neonatal TSH concentrations above 5 mU/L below 3% has been proposed as the threshold indicating iodine sufficiency. The objective of the present study was to evaluate feasibility and usefulness of nation-wide neonatal TSH concentration screening results to assess iodine status in Belgium. All newborns born in Belgium during the period 2009–2011 (n = 377713) were included in the study, except those suffering from congenital hypothyroidism and premature neonates. The frequency of neonatal TSH concentrations above 5 mU/L from 2009 to 2011 in Belgium fluctuated between 2.6 and 3.3% in the centres using the same TSH assay. There was a significant inverse association between neonatal TSH level and birth weight. The longer the duration between birth and screening, the lower the TSH level. Neonatal TSH levels were significantly lower in winter than in spring or autumn and significantly lower in spring and summer than in autumn while significantly higher in spring compared to summer. In conclusion, despite that pregnant women in Belgium are mildly iodine deficient, the frequency of neonatal TSH concentrations above 5 mU/L was very low, suggesting that the neonatal TSH threshold proposed for detecting iodine deficiency needs to be re-evaluated. Although neonatal TSH is useful to detect severe iodine deficiency, it should not be recommended presently for the evaluation of iodine status in mildly iodine deficient regions.

Iodine Status in Europe in 2014

“…This is despite the fact that 60% of the women reported taking iodine supplements during gestation [14]. Interestingly, the frequency of elevated neonatal thyroid-stimulating hormone levels was still low (3%) in this population [15]. In Denmark, while the majority of pregnant women took iodine-containing supplements, the subgroup of non-users was still iodine deficient after the introduction of iodine fortification of salt [16].…”

Neonatal thyroid-stimulating hormone level is influenced by neonatal, maternal, and pregnancy factors

“…In countries that screen for congenital hypothyroidism, the surveillance of iodine status throughout the analysis of percentage of TSH neonatal screening results enables regular monitoring at no extra cost. The percentage of neonatal TSH concentration greater than 5 mIU/L indicates the iodine status of a population as follow: a frequency less than 3% indicates iodine sufficiency, a frequency of 3% to 19.9% indicates mild iodine deficiency (MID), a frequency of 20% to 39.9% indicates moderate iodine deficiency, and a frequency greater than 40% indicates severe iodine deficiency [7,8,12]. However, the cutoff of 5 mIU/L has been criticized because, in some studies, the percentage of TSH results greater than 5 mIU/L was less than 3%, although other indicators of iodine status showed that this population had MID [12,13].…”

“…That may be explained by covariates affecting TSH screening results. Indeed, previous literature showed that several factors may affect TSH concentration [12,, including maternal thyroid diseases and drugs, type of delivery, and birth conditions as well as methods and timing of TSH determination (see Table 1 for a summary of those factors). Without studying confounding factors, it may be difficult to establish the magnitude of iodine deficiency on neonatal TSH concentration, particularly if iodine deficiency is mild.…”

The results of neonatal TSH screening do not agree with indicators of the optimal iodine status of pregnant women in the Republic of Georgia

“…Despite that PW in Belgium were mildly iodine deficient, the frequency of TSH values below 5 mIU/L from 2009 to 2012 was low: from 2.6 to 3.3%. The authors conclude that the sensitivity of the neonatal thyroid to small variations of iodine intake needs to be re-evaluated and compared to neonatal thyroglobulin concentrations that may be more sensitive to smaller variations of iodine intake during pregnancy [8].…”