Iodine status in pregnant women in northern Spain. Effect of iodised salt and iodine supplements on thyroid function.

INTRODUCTION: Iodine deficiency is linked to thyroid dysfunction, particularly in pregnant women. The objective of this study was to ascertain the iodine levels of women in the second trimester of pregnancy, analysing the influence of iodine ingestion on urinary iodine concentration (UIC) and maternal thyroid function. METHODS: A prospective observational study of pregnant women from Health Area IV of Asturias (northern Spain) recruited before 13 weeks of gestation between May and June 2017. A questionnaire on iodine intake was completed at the first visit, and urine and serum samples were collected at baseline and again during the second trimester. UIC, thyroid stimulating hormone (TSH) and free thyroxine (FT4) obtained in the second trimester of gestation were analysed and related to iodine intake. Thyroid autoimmunity was also analysed in half of the pregnant women at baseline. RESULTS: A total of 241 pregnant women were studied. Of these, 56.7% used iodised salt, 46.7% consumed ≥2 servings of dairy products daily and 88.1% took iodine supplements. Median UIC was 191µg/l (135.3-294µg/l), with 68.1% of the women having UIC ≥150µg/l. Only iodised salt consumption provided protection against iodine deficiency (odds ratio 0.35 [0.20-0.63], p=0.001). In women with no autoimmune thyroid disease (n=88), mean levels of TSH were lower in those that consumed iodised salt than in those that did not (respectively, 2.08±0.89mIU/l vs. 2.56±1.02mIU/l, p=0.025). In women with autoimmune thyroid disease (n=30), mean levels of TSH were higher in those that took iodine supplements than in those that did not (respectively, 2.97±1.25mIU/l vs. 1.16±0.41mIU/l, p=0.002). CONCLUSIONS: The pregnant women studied from Health Area IV in Asturias maintain adequate nutritional iodine status in the second trimester of gestation. In our sample, only the consumption of iodised salt was associated with adequate iodine nutrition, without affecting maternal thyroid function. Most of the women used iodine supplements, which was linked to higher levels of TSH in pregnant women with autoimmune thyroid disease.

Neonatal TSH as a marker of iodine nutrition status. Effect of maternal ioduria and thyroid function on neonatal TSH.

INTRODUCTION: Neonatal thyroid stimulating hormone (nTSH) is a marker of iodine nutrition status in the population. The WHO considers a prevalence of less than 3% of nTSH levels greater than 5 mIU/L in samples obtained within 72h from birth indicative of iodine sufficiency. The aim of this study was to determine the prevalence of nTSH levels greater than 5 mIU/L in an iodine-sufficient population and its association with maternal, neonatal and obstetric factors. MATERIALS AND METHODS: A total of 243 pregnant women were recruited between May and June 2017 in our health area. A questionnaire of iodine intake was administered, in addition to determination of ioduria, thyroid function and autoimmunity in the first trimester of gestation. We analysed nTSH levels in samples collected between 48 and 72h post birth and other obstetric and neonatal factors. RESULTS: The mean nTSH level (standard deviation) was 2.43 (1.68 mIU/L), with 7.8% of neonates having levels greater than 5 mIU/L. The highest nTSH levels corresponded to neonates of mothers with insufficient ioduria (P = 0.021) or TSH levels greater than 2.5 mIU/L, in both the case of negative (P = 0.049) and positive (P = 0.006) thyroid autoimmunity results. Maternal ioduria less than 150 µg/L was a risk factor for nTSH levels greater than 5 mIU/L (3.70 [1.06-14.60]; P = 0.046), while a neonatal weight of 2500 g or greater was a protective factor (0.14 [0.02-1.00]; P = 0.038). CONCLUSIONS: The prevalence of nTSH levels greater than 5 mIU/L in our health area was high based on the WHO recommendations. Maternal iodine deficiency was associated with a higher risk of nTSH levels greater than 5 mIU/L. Given that nTSH is currently measured before 72h post birth, we need new cut-off points to keep on using nTSH as a marker of iodine nutritional status.