Iodine Prophylaxis Using Iodized Salt and Risk of Maternal Thyroid Failure in Conditions of Mild Iodine Deficiency

Self Cite

Objective: To longitudinally evaluate the timing of maternal thyroid underfunction occurrence in mildly iodine-deficient (ID) pregnant women, and ultimately assess the benefit of thyroid function testing at early gestation only in identifying maternal thyroid underfunction. Participants/methods: Serum free-thyroxine and TSH were measured in 220 consecutive women once in early pregnancy (by week 12) and twice per trimester subsequently. Anti-thyroperoxidase and antithyroglobulin were also determined at initial and final observation. Results: Thyroid autoantibodies were detectable in 8.2% women. Overall, the prevalence of hypothyroidism over the course of gestation was 11.8% (26/220), with a relative risk of hypothyroidism in antibody-positive women of 5.0 (c 2 20.02, P!0.0005). Nonetheless, almost 70% hypothyroid women tested negative for thyroid autoantibodies. Fifteen/26 (57.7%) hypothyroid women were identified at presentation, and the remaining 11 at either early (6/11) or late (5/11) phases of the 2nd trimester. Isolated hypothyroxinemia was observed in 56/220 (25.4%) women, mostly from the 2nd trimester onwards. Conclusions: In mildly ID areas thyroid function testing early in gestation seems to be only partly effective in identifying thyroid underfunction in pregnant women. Indeed, in our series more than 40% hypothyroid women would not have been diagnosed had we limited our observation to early thyroid function tests alone. Although thyroid autoimmunity carried a 5-fold increased risk of hypothyroidism, iodine deficiency seems to be a major determinant in the occurrence of thyroid underfunction. Adequate iodine supplementation should be strongly recommended to meet the increased hormone demand over gestation.

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Gestational thyroid function abnormalities in conditions of mild iodine deficiency: early screening versus continuous monitoring of maternal thyroid status

Moleti

Presti

Mattina

et al. 2009

Self Cite

“…Nine RCTs (24,25,26,27,28,29,30,31,32) and eight observational studies (33,34,35,36,37,38,39,40) were included in the review. Seven RCTs were reported on the effects of maternal supplementation on maternal thyroid function (26,27,28,29,30,31,32,33,34,35,36,37,38,39,40). Of these, four RCTs also contained data on neonatal thyroid function (27,29,30,32).…”

Section: Study Selectionmentioning

confidence: 99%

THERAPY OF ENDOCRINE DISEASE: Impact of iodine supplementation in mild-to-moderate iodine deficiency: systematic review and meta-analysis

Taylor

Okosieme

Dayan

et al. 2014

137

Background: Although the detrimental effects of severe iodine deficiency are well recognised, the benefits of correcting mild-to-moderate iodine deficiency are uncertain. Objectives: We undertook a systematic review of the impact of iodine supplementation in populations with mildto-moderate iodine deficiency. Methods: We searched Medline and the Cochrane library for relevant articles published between January 1966 and April 2013, which investigated the effect of iodine supplementation on maternal and newborn thyroid function, infant neurodevelopment and cognitive performance in school-age children. The quality of studies was graded and eligible trials were evaluated in the meta-analysis. Results: Nine randomised controlled trials (RCTs) and eight observational studies met the inclusion criteria. Controlled trials on infant neurodevelopment were lacking; gestational iodine supplementation reduced maternal thyroid volume and serum thyroglobulin and in some studies prevented a rise in serum thyroid-stimulating hormone. None of the intervention trials recorded an excess frequency of thyroid dysfunction in contrast to observational studies. A pooled analysis of two RCTs which measured cognitive function in school-age children showed modest benefits of iodine supplementation on perceptual reasoning (standardised mean difference (SMD) 0.55; 95% CI 0.05, 1.04; PZ0.03) and global cognitive index (SMD 0.27; 95% CI 0.10, 0.44; PZ0.002) with significant heterogeneity between studies. Conclusion: Iodine supplementation improves some maternal thyroid indices and may benefit aspects of cognitive function in school-age children, even in marginally iodine-deficient areas. Further large prospective controlled studies are urgently required to clarify these findings and quantify the risk/benefits of iodine supplementation in regions previously believed to be iodine sufficient such as the UK.

“…It is also important to ensure an adequate supply of iodine during pregnancy for many reasons including optimizing the fetal thyroid stores, which are required for its normal start of function at 20 weeks, gestation (13,97). It has been unequivocally demonstrated that a good nutritional status of iodine, related to iodized salt, bread, and milk consumption over prolonged periods before pregnancy, can reduce the risk of TD during gestation (98,99). In populations with known iodine deficiency, supplementation with a minimum of 150-200 mg of iodine during pregnancy and lactation ensures the recommended intake is achieved.…”

Section: How and When Should All This Be Done?mentioning

confidence: 99%

CONTROVERSIES IN ENDOCRINOLOGY: On the need for universal thyroid screening in pregnant women

Vila

Velasco

González

et al. 2014

There is a well-known controversy among scientific societies regarding the recommendation to screen for thyroid dysfunction (TD) during pregnancy. Although several studies have shown an association between maternal subclinical hypothyroidism and/or hypothyroxinemia with obstetric problems and/or neurocognitive impairment in the offspring, there is only limited evidence on the possible positive effects of thyroxine (T 4 ) treatment in such cases. Despite the scarcity of this evidence, there is a widespread agreement among clinicians on the need for treatment of clinical hypothyroidism during pregnancy and the risks that could arise due to therapeutic abstention. As maternal TD is a quite prevalent condition, easily diagnosed and for which an effective and safe treatment is available, some scientific societies have proposed to assess thyroid function during the first trimester of pregnancy and ideally before week 10 of gestational age. Given the physiologic changes of thyroid function during pregnancy, hormone assessment should be performed using trimester-specific reference values ideally based on locally generated data as geographic variations have been detected. Screening of TD should be based on an initial determination of TSH performed early during the first trimester and only if abnormal should it be followed by either a free or total T 4 measurement. Furthermore, adequate iodine supplementation during pregnancy is critical and if feasible it should be initiated before the woman attempts to conceive.