Urinary iodine and thyroid function in a population of healthy pregnant women in the North of Spain

Reference ranges of thyroid hormones during the first trimester in Catalan women using the Atellica® IM Solution Immunoassay Analyzer

BACKGROUND

Gestational hypothyroidism has been shown to be associated with adverse pregnancy outcomes as well as adverse outcomes for the child. Thyroid hormones concentrations change in gestation, especially within the first trimester, so the results of thyroid function test often are outside non-pregnant reference ranges. The objective of this study was to establish the first trimester reference ranges for thyroid stimulating hormone (TSH) and free thyroxine (FT4) for pregnant women in Barcelona (Spain).

METHODS

It was a prospective study in which 673 women were recruited during their first trimester of gestation (8-13 weeks). Serum TSH, FT4 and antithyroid peroxidase antibodies (TPOAb) were measured with Atellica® IM 1600 (Siemens Healthineers). After excluding 418 women, the reference ranges for TSH and FT4 were calculated by the 2.5th and 97.5th percentiles. Potential variables examined in this study were age, body mass index (BMI), ethnicity, iodine supplementation and smoking habit.

RESULTS

The reference ranges established on the Atellica® IM 1600 for the first trimester pregnancy in our population were 0.111 to 4.291 mIU/L for TSH and 11.45 to 17.76 pmol/L for FT4. No significant differences were found in thyroid hormones concentrations regarding maternal age (≤30 years vs >30 years) (p = .117), iodine supplementation (p = .683) and smoking habit (p = .363). The prevalence of TPOAb was estimated at 10.0%.

CONCLUSIONS

We found that in our local population, the optimal TSH upper reference limit in the first trimester of gestation was 4.3 mIU/L, similar to that proposed by de ATA-2017 guideline (4.0 mIU/L).

Maternal Thyroid Function During Pregnancy and Offspring White Matter Microstructure in Early Adulthood: A Prospective Birth Cohort Study

Background: The fetus is fully dependent on maternal thyroid hormones until mid-gestation and suboptimal maternal thyroid function has been associated with alterations in the neurodevelopment of the offspring. We used maternal free thyroxine (fT4) and thyrotropin (TSH) levels in early gestation to study the association of maternal thyroid function during early pregnancy and offspring brain white matter (WM) integrity in early adulthood. Methods: Our study population consisted of a total of 292 mother-child pairs. Maternal fT4 and TSH were used as predictors and offspring multimodal imaging measures of fractional anisotropy, mean diffusivity, and magnetization transfer ratio (FA, MD, and MTR) as dependent variables. First, as Global analysis, all analyzed 14 WM tracts were studied simultaneously using linear-mixed effect models. Second, if a global effect was detected, a post hoc Tract-wise analysis was carried out using linear models individually in each WM tract. Study population was stratified by sex. Results: We found a positive association between maternal fT4 and offspring Global FA in males when adjusted for all maternal and offspring covariates (n = 114; β = 0.154; confidence interval = 0.045-0.263; p = 0.006). The finding was observed to be driven by multiple WM tracts, of which three projection fiber tracts and the forceps minor survived correcting for multiple comparisons in Tract-wise analysis. Conclusions: Maternal thyroid function in early pregnancy was observed to be associated with WM microstructure in male offspring in early adulthood. Our results suggest that maternal fT4 levels in early pregnancy may modulate axonal characteristics, with a long-term effect on offspring WM development.

Relationship between mild iodine deficiency in pregnant women and thyroid function: A meta-analysis

BACKGROUND

Pregnant women are among the key groups in iodine nutrition evaluation. The purpose of the present study was to summarize the evidence supporting the relationship between mild iodine deficiency (UIC: 100-150 μg/L) in pregnant women and levels of thyroid function tests.

METHODS

This review follows the guidelines for systematic reviews (PRISMA 2020). Three electronic databases (PubMed, Medline, and Embase) were searched for relevant publications in English on the association between mild iodine deficiency in pregnant women and thyroid function. Articles published in Chinese were searched in China's electronic databases (CNKI, WanFang, CBM, and WeiPu). Pooled effects were presented as standardized mean differences (SMDs) and odds ratios (ORs) with 95% confidence intervals (CIs) using fixed or random effect models, respectively. This meta-analysis was registered at www.crd.york.ac.uk/prospero as CRD42019128120.

RESULTS

We summarized the results from 7 articles with 8261 participants. The overall pooled results showed that the levels of FT₃, FT4, and abnormal TgAb (the antibody levels exceeded the upper limit of the reference range) were significantly increased in pregnant women with mild iodine deficiency compared to pregnant women with adequate iodine status (FT₃: SMD=0.854, 95% CI: 0.188, 1.520; FT₄: SMD=0.550, 95% CI: 0.050, 1.051; TgAb: OR=1.292, 95% CI: 1.095; 1.524). Subgroup analysis was carried out on the sample size, ethnicity, country, and gestation of FT₃, FT_4, and TSH, but no plausible factor was found. Egger's tests indicated no publication bias.The increase in FT₃ and FT_4, as well as TgAb levels, in pregnant women is associated with mild iodine deficiency.

CONCLUSION

Mild iodine deficiency is associated with an increase in FT_3，FT₄ and TgAb levels in pregnant women. Mild iodine deficiency may increase the risk of thyroid dysfunction in pregnant women.

Management of Hyperthyroidism during Pregnancy: A Systematic Literature Review

In pregnancy, several physiological changes affect maternal circulating thyroid hormone levels. The most common causes of hyperthyroidism in pregnancy are Graves' disease and hCG-mediated hyperthyroidism. Therefore, evaluating and managing thyroid dysfunction in women during pregnancy should ensure favorable maternal and fetal outcomes. Currently, there is no consensus regarding an optimal method to treat hyperthyroidism in pregnancy. The term "hyperthyroidism in pregnancy" was searched in the PubMed and Google Scholar databases to identify relevant articles published between 1 January 2010 and 31 December 2021. All of the resulting abstracts that met the inclusion period were evaluated. Antithyroid drugs are the main therapeutic form administered in pregnant women. Treatment initiation aims to achieve a subclinical hyperthyroidism state, and a multidisciplinary approach can facilitate this process. Other treatment options, such as radioactive iodine therapy, are contraindicated during pregnancy, and thyroidectomy should be limited to severe non-responsive thyroid dysfunction pregnant patients. In light of this events, even in the absence of guidelines certifying screening, it is recommended that all pregnant and childbearing women should be screened for thyroid conditions.

Iodine status of pregnant women with obesity from inner city populations in the United Kingdom

BACKGROUND/OBJECTIVES

Iodine is essential for foetal neurodevelopment and growth. Requirements increase in pregnancy to support increased thyroid hormone synthesis for maternal and foetal requirements, and for foetal transfer. Iodine deficiency in pregnancy is widely reported, and obesity has been associated with sub-optimal thyroid function. We evaluated iodine status and its relation with birthweight in a secondary analysis of pregnant women with obesity from multi-ethnic inner-city settings who participated in the UK Pregnancies Better Eating and Activity trial (UPBEAT).

SUBJECTS/METHODS

Iodine and creatinine concentrations were evaluated in spot urine samples in the second (15⁺⁰-18⁺⁶ weeks, n = 954) trimester of pregnancy. We assessed iodine status as urinary iodine concentration (UIC) and urinary iodine-to-creatinine ratio (UI/Cr) and applied WHO/UNICEF/IGN population threshold of median UIC > 150 µg/L for iodine sufficiency. Relationships between iodine status and birthweight were determined using linear and logistic regression with appropriate adjustment, including for maternal BMI and gestational age.

RESULTS

Median (IQR) UIC and UI/Cr in the second trimester of pregnancy were 147 µg/L (99-257) and 97 µg/g (59-165), respectively. An UI/Cr <150 μg/g was observed in 70% of women. Compared to women with UI/Cr >150 µg/g, there was a trend for women with UI/Cr <150 µg/g to deliver infants with a lower birthweight (β = -60.0 g; 95% CI -120.9 to -1.01, P = 0.05).

CONCLUSIONS

Iodine status of pregnant women with obesity from this cohort of UK women was suboptimal. Lower iodine status was associated with lower birthweight.

Impact of Dietary Habit, Iodine Supplementation and Smoking Habit on Urinary Iodine Concentration During Pregnancy in a Catalonia Population

(1) Background: The nutritional status of women during pregnancy can have a considerable effect on maternal and fetal health, and on the perinatal outcome. Aim: to assess the changes occurring in dietary iodine intake, potassium iodide supplementation, and smoking habit, and the impact of these changes on the urinary iodine concentration (UIC) during pregnancy in a population of women in Catalonia (Spain). (2) Methods: Between 2009–2011, an observational study included a cohort of women whose pregnancies were monitored in the public health system in the Central and North Metropolitan areas of Catalonia. Women received individual educational counseling, a dietary questionnaire was completed, and a urine sample was collected for iodine determination at each trimester visit. (3) Results: 633 (67.9%) women answered the questionnaire at all 3 visits. The percentage of women with a desirable UIC (≥150 μg/L) increased from the first to the second trimester and remained stable in the third (57.3%, 68.9%, 68%; p < 0.001). Analysis of the relationship between UIC ≥ 150 μg/L and the women’s dietary habits showed that the percentage with UIC ≥ 150 μg/L increased with greater consumption of milk in the first trimester, and the same was true for iodized salt use in all three trimesters and iodine supplementation in all three. (4) Conclusion: During pregnancy, increased intake of milk, iodized salt, and iodine supplements were associated with an increase in the UIC.

Trimester-Specific Thyroid Function in Pregnant Women with Different Iodine Statuses

OBJECTIVES

To explore trimester-specific thyroid function changes under different iodine statuses throughout pregnancy.

METHODS

A cross-sectional study was conducted to assess the pregnancy iodine status, and 2,378 healthy pregnant women covering all 3 trimesters were recruited. Urinary iodine concentration (UIC) was measured by collecting spot urine samples. Blood samples were collected to evaluate thyroid function. Thyroid B-ultrasonography was conducted to measure the thyroid volume (Tvol).

RESULTS

The median UIC was 168 μg/L (111-263 μg/L). The UIC, free triiodothyronine (FT3), and free thyroxine (FT4) were significantly decreased as the pregnancy progressed (p < 0.001, p for trend <0.001), while Tvol increased (p < 0.001, p for trend <0.001). Thyrotropin (TSH) was significantly different between the 3 trimesters and showed an upward trend (p < 0.001), but the p for trend was not significant (p for trend = 0.88). After stratification by UIC, there were no significant differences in serum TSH, FT4, or FT3 level between UIC groups. Tvol was significantly higher in the UIC ≥500 μg/L group in the first trimester (β: 2.41, 95% CI: 1.09-3.72, p <0.001), as well as in the 250 ≤ UIC < 500 μg/L group (β: 1.65, 95% CI: 0.61-2.70, p < 0.001) and UIC ≥500 μg/L group (β: 3.35, 95% CI: 1.96-4.74, p < 0.001) in the third trimester.

CONCLUSIONS

No difference was observed in TSH, FT3, or FT4 among the different iodine status groups throughout pregnancy. Tvol increased as the pregnancy progressed, and it was especially higher in the UIC ≥500 μg/L group in the first and third trimesters.

Universal screening for thyroid disease during pregnancy should be performed

Thyroid disease can significantly impact the pregnant woman and her child. Human and animal studies have firmly linked overt hypothyroidism and overt hyperthyroidism to miscarriage, preterm delivery and other adverse pregnancy outcomes. Overt hypothyroidism and overt hyperthyroidism affect 1% of all pregnancies. Treatment is widely available, and if detected early, results in decreased rates of adverse outcomes. Universal screening for thyroid disease in pregnancy can identify patients with thyroid disease requiring treatment, and ultimately decrease rates of complications. Universal screening is cost-effective compared to the currently accepted practice of targeted screening and may even be cost-saving in some healthcare systems. Targeted screening, which is recommended by most professional associations, fails to detect a large proportion of pregnant women with thyroid disease. In fact, an increasing number of providers are performing universal screening for thyroid disease in pregnancy, contrary to society guidelines. Limited evidence concerning the impact of untreated and treated subclinical disease and thyroid autoimmunity has distracted from the core rationale for universal screening - the beneficial impact of detecting and treating overt thyroid disease. Evidence supporting universal screening for overt disease stands independently from that of subclinical and autoimmune disease. The time to initiate universal screening is now.

Effect of levothyroxine supplementation on pregnancy loss and preterm birth in women with subclinical hypothyroidism and thyroid autoimmunity: a systematic review and meta-analysis

BACKGROUND

Subclinical hypothyroidism (SCH) and thyroid autoimmunity (TAI) are associated with adverse pregnancy outcomes such as pregnancy loss and preterm birth. However, the ability of levothyroxine (LT4) supplementation to attenuate the risks of these outcomes remains controversial.

OBJECTIVE AND RATIONALE

This systematic review and meta-analysis was conducted to determine the effect of LT4 supplementation on pregnancy loss rate (PLR) and preterm birth rate (PBR) among pregnant women with SCH and TAI.

SEARCH METHODS

A systematic literature search of the PubMed, EMBASE, Web of Science and Cochrane Controlled Trials Register databases and Clinicaltrials.gov was performed to identify all relevant English studies published up to April 2018. The following terms were used for the search: [subclinical hypothyroidism OR thyroid autoimmunity OR thyroperoxidase antibody (TPO-Ab) OR thyroglobulin antibodies (Tg-Ab)] AND (levothyroxine OR euthyrox) AND [pregnancy outcome OR miscarriage OR abortion OR pregnancy loss OR preterm birth OR premature delivery OR early labo(u)r]. The reference lists of the relevant publications were also manually searched for related studies. Published manuscripts were included if they reported data on pregnancy loss, preterm birth or both. We separately analysed the pooled effects of LT4 supplementation on PLR and PBR in women with SCH and TAI.

OUTCOMES

Overall, 13 eligible studies including 7970 women were included in the meta-analysis. Eight and five of these studies were randomized controlled trials (RCTs) and retrospective studies, respectively. The pooled results indicated that LT4 supplementation significantly decreased the PLR [relative risk (RR) = 0.56, 95% confidence interval (CI): 0.42-0.75, I2 = 1%, 12 studies] and PBR (RR = 0.68, 95% CI: 0.51-0.91, I2 = 21%, eight studies) in women with SCH and/or TAI. We further found that LT4 supplementation significantly decreased the risk of pregnancy loss (RR = 0.43, 95% CI: 0.26-0.72, P = 0.001, I2 = 0%) but not of preterm birth (RR = 0.67, 95% CI: 0.41-1.12, P = 0.13, I2 = 0%) in women with SCH. Furthermore, LT4 supplementation significantly decreased the risks of both pregnancy loss (RR = 0.63, 95% CI: 0.45-0.89, P = 0.009, I2 = 0%) and preterm birth (RR = 0.68 95% CI: 0.48-0.98, P = 0.04, I2 = 46%) in women with TAI. These results were consistent when only RCTs were included in the analysis. Further, in women with SCH, LT4 supplementation reduced the risk of pregnancy loss in pregnancies achieved by assisted reproduction (RR = 0.27, 95% CI: 0.14-0.52, P < 0.001, I2 = 14%) but not in naturally conceived pregnancies (RR = 0.60, 95% CI: 0.28-1.30, P = 0.13, I2 = 0%). By contrast, in women with TAI, LT4 supplementation reduced the risks of both pregnancy loss (RR = 0.61, 95% CI: 0.39-0.96, P = 0.03, I2 = 0%) and preterm birth (RR = 0.49, 95% CI: 0.30-0.79, P = 0.003, I2 = 0%) in naturally conceived pregnancies but not in pregnancies achieved by assisted reproduction (RR = 0.68, 95% CI: 0.40-1.15, P = 0.15, I2 = 0% for pregnancy loss and RR = 1.20, 95% CI: 0.68-2.13, P = 0.53, I2 not applicable for preterm birth).

WIDER IMPLICATIONS

This meta-analysis confirmed the beneficial effects of LT4 supplementation, namely the reduced risks of pregnancy loss and preterm birth, among pregnant women with SCH and/or TAI. The different effects of LT4 supplementation on naturally conceived pregnancies and pregnancies achieved by assisted reproduction in women with SCH and/or TAI suggest that these women should be managed separately. Due to the limited number of studies included in this meta-analysis, especially in the subgroup analysis, further large RCTs and fundamental studies are warranted to confirm the conclusions and better clarify the molecular mechanism underlying these associations.

Change over time in the iodine nutritional status of pregnant women from the Pamplona healthcare region

INTRODUCTION

Adequate iodine intake is essential during pregnancy. A previous study of pregnant women from the Pamplona healthcare region showed mild iodine deficiency (mean urinary iodine level, 125 mcg/L). This study was intended to ascertain the iodine intake of pregnant women in our region and to analyze the change over time in their iodine nutritional status.

METHODS

An observational study of 400 women in their first trimester of pregnancy. An iodine intake questionnaire was administered. To assess iodine status, urinary iodine concentration (UIC) was measured in a simple urine sample, and serum thyroglobulin levels were determined. In addition, thyroid volume was measured by cervical ultrasound examination.

RESULTS

Iodized salt was used by 70.5% of all participants (55.3% since the pre-gestational period) and 98.5% of them received iodine-containing supplements (mean dose, 202.6±30.1 mcg/day). Mean urinary iodine concentration was 242 mcg/L (138.5-415.5 mcg/L) and the mean serum thyroglobulin level was 12.3 mcg/L (8.3-9 mcg/L). Iodized salt intake was associated with higher UICs and lower thyroid volume. No differences were found in any of the tested parameters regarding the intake of dairy products, fish, or eggs.

CONCLUSIONS

Iodine intake by pregnant women in Pamplona has increased due to a greater use of iodized salt and to higher doses of iodine supplements. As a result of this, an adequate iodine status has been achieved in the last decade.

Moderate Iodine Deficiency Is Common in Pregnancy but Does Not Alter Maternal and Neonatal Thyroid Function Tests

INTRODUCTION

An Israeli national survey found that 85% of pregnant women had urinary iodine content (UIC) levels below the adequacy range (<150 µg/L). Widespread desalinated water usage and no national fortification plan are possible causes. Studies assessing relationships between iodine status and maternal and neonatal thyroid function provided varying results. Our aims were to determine whether iodine deficiency was associated with altered maternal or neonatal thyroid function and the factors leading to iodine deficiency.

METHODS

A cross-sectional study including 100 healthy women without prior thyroid disease, in their first trimester of a singleton pregnancy were recruited from an HMO clinic in central Israel. The women were followed from their first trimester. All women completed a 24-h dietary recall and life habits questionnaires. We tested for UIC, maternal and neonatal thyroid function, maternal autoantibodies, and neonatal outcomes.

RESULTS

Median UIC in our cohort was 49 µg/L [25%-75% interquartile range (IQR) 16-91.5 µg/L], with 84% below adequacy range. No correlation was found between iodine deficiency and maternal or neonatal thyroid function which remained within normal ranges. Antibody status did not differ, but thyroglobulin levels were significantly higher in iodine insufficient subjects. UIC was higher in women consuming an iodine containing supplement. There was no association between UIC and dietary iodine content or water source.

CONCLUSIONS

Moderate iodine deficiency is common in our healthy pregnant women population. Our data imply that moderate iodine deficiency in pregnancy seem sufficient to maintain normal maternal and neonatal thyroid function.

The Association of Maternal Iodine Status in Early Pregnancy with Thyroid Function in the Swedish Environmental Longitudinal, Mother and Child, Asthma and Allergy Study

Background: Severe maternal iodine deficiency can impact fetal brain development through effects on maternal and/or fetal thyroid hormone availability. The effects of mild-to-moderate iodine deficiency on thyroid function are less clear. The aim was to investigate the association of maternal urinary iodine concentration corrected for creatinine (UI/Creat) with thyroid function and autoantibodies in a mild-to-moderate iodine-deficient pregnant population. Methods: This study was embedded within the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy (SELMA) study. Clinical reference ranges were determined by the 2.5th and 97.5th population-based percentile cutoffs. The associations of UI/Creat with thyrotropin (TSH), free thyroxine (fT4), free triiodothyronine (fT3), total T4 (TT4), and total T3 (TT3) were studied using multivariable linear regression in thyroid peroxidase antibody (TPOAb)-negative women. The association of UI/Creat with TPOAb and thyroglobulin antibody (TgAb) positivity was analyzed using multivariable logistic regression. Results: Urinary iodine and thyroid function were measured at a median (95% range) gestational age of 10 (6-14) weeks in 2009 women. The median (95% range) UI/Creat was 85 μg/g (36-386) and the UI/Creat was below 150 μg/g in 80.1% of women. Reference ranges did not differ substantially by UI/Creat. A lower UI/Creat was associated with a lower TSH (p = 0.027), a higher TT4 (p = 0.032), and with a corresponding trend toward slightly higher fT4 (p = 0.081), fT3 (p = 0.079), and TT3 (p = 0.10). UI/Creat was not associated with the fT4/fT3 (p = 0.94) or TT4/TT3 ratios (p = 0.63). Women with a UI/Creat of 150-249 μg/g had the lowest prevalence of TPOAb positivity (6.1%), while women with a UI/Creat of <150 μg/g had a higher prevalence (11.0%, odds ratio [OR] confidence interval [95% CI] 1.84 [1.07-3.20], p = 0.029). Women with a UI/Creat ≥500 μg/g showed the highest prevalence and a higher risk of TPOAb positivity, however, only a small proportion of women had such a UI/Creat (12.5%, OR, [95% CI] 2.36 [0.54-10.43], p = 0.26). Conclusions: We could not identify any meaningful differences in thyroid function reference ranges. Lower iodine availability was associated with a slightly lower TSH and a higher TT4. Women with adequate iodine intake had the lowest risk of TPOAb positivity.

Insufficient iodine intake in pregnant women in different regions of the world: a systematic review

OBJECTIVE

To determine the prevalence of insufficient iodine intake in pregnant women.

MATERIALS AND METHODS

The search was performed in the electronic databases Medline (PubMed), Latin American and Caribbean Literature in Health Sciences (Lilacs) and Scopus. Review studies, experimental studies, those with adolescent pregnant women (< 20 years) and iodine supplementation were excluded. The selection followed the steps of identifying the articles in the databases, deleting the duplicates, and reading the titles, abstracts, and then the entire article. The search for the articles occurred in September 2017, using the descriptors "pregnant" and "iodine deficiency" NOT "supplementation" in English, Portuguese and Spanish.

RESULTS

Thirteen articles were included, the deficiency prevalence ranged from 16.1% to 84.0%, and the median of iodine intake was insufficient in 75% of the studies. There is no classification for mild, moderate or severe levels of iodine deficiency in pregnant women, which makes it impossible to know the real dimension of the problem.

CONCLUSION

The high prevalence of insufficient iodine intake in pregnant women, observed worldwide, shows the need for a population classification in order to direct public policies. Arch Endocrinol Metab. 2019;63(3):306-11.

Thyroid Function Reference Values in Healthy Iodine-Sufficient Pregnant Women and Influence of Thyroid Nodules on Thyrotropin and Free Thyroxine Values

BACKGROUND

Thyroid function assessment in pregnancy requires specific reference intervals stratified by gestational age and according to each laboratory method. Thyroid nodules may influence thyroid function in pregnant women. The aims of this study were to define the reference values of thyrotropin (TSH) and free thyroxine (fT4) in the three pregnancy trimesters in iodine-sufficient pregnant women, and to analyze the influence of thyroid nodules on thyroid function during pregnancy.

METHODS

This was a prospective, longitudinal study comprising 400 pregnant women with no history of thyroid disease and no medication influencing thyroid function. TSH, fT4, antithyroglobulin, and antithyroid peroxidase antibodies were measured each trimester by chemiluminescent immunoassays. Urinary iodine concentration was measured in the first trimester when a thyroid echography was also performed. Women with multiple gestation pregnancies, positive thyroid autoimmunity, TSH values >5 or <0.1 mIU/L with a simultaneous fT4 level above the general population reference value in the first trimester, or clinically significant thyroid nodules (nodules ≥1 cm and/or multiple nodules) were excluded to establish TSH and fT4 reference values.

RESULTS

Reference intervals in the first, second, and third trimesters were 0.13-4.16, 0.31-3.73, and 0.58-4.36 mIU/L, respectively, for TSH, and 0.85-1.24, 0.82-1.20, and 0.67-1.06 ng/dL, respectively, for fT4. The total prevalence of thyroid nodules was 28.8% [95% confidence interval (CI) 24.4-33.5%], and 6.0% of the participants showed clinically significant nodules. Pregnant women with thyroid nodules (n = 115) showed consistently lower TSH values during all pregnancy stages (first trimester: median 1.14 mIU/L [interquartile range (IQR) 0.53-1.75 mIU/L] vs. 1.48 mIU/L [IQR 0.94-2.19 mIU/L], p < 0.001; second trimester: 1.22 mIU/L [IQR 0.66-1.77 mIU/L] vs. 1.45 mIU/L [1.04-2.05 mIU/L], p = 0.001; third trimester: 1.74 mIU/L [IQR 1.08-2.36 mIU/L] vs. 1.93 mIU/L [IQR 1.37-2.58 mIU/L], p = 0.041) and higher fT4 values in the first trimester (M ± SD = 1.08 ± 0.14 ng/dL vs. 1.03 ± 0.12, p < 0.001) compared to those without nodules (n = 285). Both pregnant women with clinically significant thyroid nodules and those with nonsignificant ones had lower TSH values than women without nodules.

CONCLUSIONS

TSH/fT4 reference intervals in pregnant women from the authors' geographical area will thyroid dysfunction in pregnancy to be appropriately diagnosed. The prevalence of thyroid nodules is high in iodine-sufficient pregnant women, and is associated with low TSH values across pregnancy.

The joint role of thyroid function and iodine concentration on gestational diabetes risk in a population-based study

INTRODUCTION

Iodine is essential for thyroid function, and iodine deficiency during pregnancy is common in Europe and the USA. However, no published studies have examined the role of iodine deficiency in the relation between thyroid function and gestational diabetes mellitus (GDM).

MATERIAL AND METHODS

We conducted a population-based, nested case-control study within the Finnish Maternity Cohort using pregnancy and perinatal outcome data from the Finnish Maternal Birth Register. We randomly selected 224 GDM cases with singleton pregnancies and 224 controls without GDM from all singleton births occurring in Finland during 2012-2013. Blood was drawn at 10-14 weeks' gestation and analyzed for serum iodide, thyroglobulin, and thyroid-stimulating hormone (TSH) concentrations. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CI) of GDM.

RESULTS

Very high thyroglobulin concentration (>95% percentile; >83 μg/L) was not associated with significantly altered odds of GDM compared to those with normal levels (OR 0.41; 95% CI: 0.12, 1.38). High concentrations of TSH were also not associated with increased odds of GDM compared to normal levels of TSH (OR 0.45; 95% CI: 0.06, 3.18). Women in the lowest 5th percentile (<1.58 ng/mL) of iodine did not have increased odds of GDM compared to those with iodide in the highest quartile (OR 0.39; 95% CI: 0.11, 1.35).

CONCLUSIONS

Low levels of iodide and thyroid function in early pregnancy are not associated with increased risk of GDM in this mildly iodine-deficient population.

Differences in Diagnostic Criteria Mask the True Prevalence of Thyroid Disease in Pregnancy: A Systematic Review and Meta-Analysis

BACKGROUND

The reported prevalence of thyroid disease in pregnancy varies widely through the published literature. These discrepancies are due to differences in criteria for euthyroidism, nationality, iodine status, and gestational age at screening. As a result, currently, an accepted rate of prevalence does not exist for the various thyroid diseases in pregnancy. Understanding the true prevalence rates of these disorders has important implications for clinical management and the ongoing discussion regarding universal screening. The aims of this study were to assess (i) the true prevalence of thyroid disorders in pregnancy and (ii) the impact of diagnostic methodology on these rates.

METHODS

A systematic review was conducted of the existing literature, including the Pubmed database and references from relevant review articles. Sixty-three studies reporting prevalence of overt hypothyroidism, subclinical hypothyroidism, isolated hypothyroxinemia, subclinical hyperthyroidism, and overt hyperthyroidism in pregnant women were included. Studies were further classified by thyrotropin (TSH) cutoff for diagnosis in hypothyroid disease and timing of screening for hyperthyroid disease. Meta-analysis yielded pooled prevalence rates, with subgroup analyses for TSH cutoff and timing of screening. Analysis of studies using the 97.5th percentile TSH cutoff was assessed to yield the most accurate prevalence rates for hypothyroidism.

RESULTS

Pooled prevalence rates for hypothyroidism calculated from studies using the 97.5th percentile as an upper limit for TSH were 0.50% for overt hypothyroidism, 3.47% for subclinical hypothyroidism, and 2.05% for isolated hypothyroxinemia. Pooled prevalence rates in the first and second trimesters for hyperthyroidism were 0.91% and 0.65%, respectively, for overt hyperthyroidism and 2.18% and 0.98%, respectively, for subclinical hyperthyroidism.

CONCLUSION

Population-based, trimester-specific TSH cutoffs for diagnosis of hypothyroid disease in pregnancy result in more accurate diagnosis and better estimates for prevalence of disease. Prevalence of hyperthyroidism in pregnancy varies depending on timing of screening. The prevalence rates reported in this study represent the best estimate to date of the true rates of thyroid disease in pregnancy.

Pregnancy outcomes of antibody negative and untreated subclinical hypothyroidism

AIM

Subclinical hypothyroidism is thought to be associated with adverse pregnancy outcomes but the data is conflicting and generally depends on antibody positivity and treatment. We evaluated the pregnancy outcomes in Turkish population with untreated, antibody negative subclinical hypothyroidism for the first time.

METHODS

We searched for 30 015 patients between January 2016 and May 2017 retrospectively. Finally, a total of 930 pregnant women with untreated, antibody negative subclinical hypothyroidism and 7986 controls were included. Demographic characteristics, laboratory findings and pregnancy outcomes, including pregnancy loss, impaired glucose tolerance, gestational diabetes, hypertensive disorders of pregnancy, preterm birth, neonatal intensive care unit admission, placenta previa and abruption, cesarean delivery, low birthweight, Apgar score <7 and premature rupture of membranes were recorded.

RESULTS

Demographic and laboratory characteristics were similar between two groups except thyroid stimulating hormone levels and previous uterine surgery rates. Subclinical hypothyroidism group had an increased risk of pregnancy loss (odds ratio [OR] 2.583; 95% confidence interval [CI] 1.982-3.365; P < 0.001), impaired glucose tolerance (OR 1.952; 95% CI 1.450-2.627; P < 0.001), hypertensive disorders of pregnancy (OR 1.476; 95% CI 1.113-1.923; P = 0.004), neonatal intensive care unit admission (OR 1.620; 95% CI 1.084-2.420; P = 0.019), placenta previa (OR 12.581; 95% CI 5.046-31.363; P < 0.001) and cesarean delivery (OR 1.263; 95% CI 1.091-1.462; P = 0.002).

CONCLUSION

Subclinical hypothyroidism has worse pregnancy outcomes as compared to euthyroid pregnant women even in antibody negativity. Therefore, we suggest that all pregnant women should routinely be screened in their first antenatal visits for thyroid functions.

Iodine Deficiency in Zhejiang Pregnant Women in the Context of Universal Salt Iodization Programme

Zhejiang introduced universal salt iodization (USI) programme in 1995 and has achieved the goal of elimination of iodine deficiency disorders (IDD) since 2011. However, no systematical data of iodine nutritional status in population in pregnancy is available. In this cross-sectional study, pregnant women were interviewed to complete questionnaires in addition to handing in samples of urine and household table salt between March 2016 to February 2017. Date of birth, age of pregnancy, ethnicity and dietary iodine habits were recorded. The overall median urinary iodine concentration in 8561 pregnant women was 130.47 µg/L, which was lower than the cut-off value of iodine sufficiency of 150 µg/L recommended by the WHO. Participants using non-iodized salt, taking non-iodine-containing supplements, in coastal and in Han group were independently associated with iodine deficiency. The current USI programme did not supply Zhejiang pregnant women with sufficient iodine intake. They are generally iodine deficient, which have great public health importance since even mild IDD in pregnancy have adverse effects on fetal neurodevelopment. We strongly recommend urgent measures to improve iodine intake in pregnancy.

Iodine Deficiency in a Study Population of Norwegian Pregnant Women-Results from the Little in Norway Study (LiN)

Iodine sufficiency is particularly important in pregnancy, where median urinary iodine concentration (UIC) in the range of 150⁻250 &micro;g/L indicates adequate iodine status. The aims of this study were to determine UIC and assess if dietary and maternal characteristics influence the iodine status in pregnant Norwegian women. The study comprises a cross-sectional population-based prospective cohort of pregnant women (Little in Norway (LiN)). Median UIC in 954 urine samples was 85 &micro;g/L and 78.4% of the samples (n = 748) were &le;150 &micro;g/L. 23.2% (n = 221) of the samples were &le;50 &micro;g/L and 5.2% (n = 50) were above the requirements of iodine intake (>250 &micro;g/L). Frequent iodine-supplement users (n = 144) had significantly higher UIC (120 &micro;g/L) than non-frequent users (75 &micro;g/L). Frequent milk and dairy product consumers (4⁻9 portions/day) had significantly higher UIC (99 &micro;g/L) than women consuming 0⁻1 portion/day (57 &micro;g/L) or 2⁻3 portions/day (83 &micro;g/L). Women living in mid-Norway (n = 255) had lowest UIC (72 &micro;g/L). In conclusion, this study shows that the diet of the pregnant women did not necessarily secure a sufficient iodine intake. There is an urgent need for public health strategies to secure adequate iodine nutrition among pregnant women in Norway.

First Israeli National Iodine Survey Demonstrates Iodine Deficiency Among School-Aged Children and Pregnant Women

BACKGROUND

National data on iodine status in Israel are lacking. Reliance on iodine-depleted desalinated water, the absence of a salt iodization program, and reports of increased use of thyroid medication in Israel suggest that the population's iodine intake is likely inadequate. The aims of this study were therefore to determine the iodine status of Israeli school-age children (SAC) and pregnant women (PW) in a nationally representative sample obtained by a novel approach of using pre-discard urinalysis samples collected from a centralized national laboratory.

METHODS

Spot urine samples from 1023 SAC and 1074 PW, representing all regions and major sectors in Israel, were collected during 2016 at the Maccabi Healthcare Services central laboratory. Urinary iodine concentration (UIC) was measured, and the results were analyzed by trimester, sex, region, and sector.

RESULTS

SAC were iodine deficient, with a median (interquartile range [IQR]) UIC of 83 μg/L (52-127 μg/L); 62% of SAC UICs were below the World Health Organization adequacy range for SAC (100-199 μg/L). PW were also iodine deficient, with a median (IQR) UIC of 61 μg/L (36-97 μg/L); 85% of PW UICs were below the adequacy range for PW (150-249 μg/L). For both SAC and PW, the median UIC was below the World Health Organization's adequacy range across all sectors, sexes, and districts. Among SAC, the median (IQR) UIC was lower among females (75 μg/L; 48-119 μg/L) than males (92 μg/L; 59-133 μg/L; p < 0.05). Median UIC values of PW correlated significantly with the median UIC for SAC by sub-district (R² = 0.3, p < 0.05).

CONCLUSIONS

Urine sampling via a centralized national laboratory was efficient and cost-saving. Iodine deficiency in Israeli SAC and PW is a serious public-health concern. A national program of salt iodization and iodine supplementation of PW should be urgently considered.

Thyroid homeostasis in mother-child pairs in relation to maternal iodine status: the MISA study

BACKGROUND/OBJECTIVES

Iodine deficiency during pregnancy may influence maternal and foetal thyroid function with the risk of causing neurocognitive and psychomotor deficits in the offspring. The objective of this study was to assess iodine status in pregnant women from Northern Norway and to investigate the influence of iodine status on maternal and infant thyroid function.

SUBJECTS/METHODS

Women from the Northern Norway Mother-and-Child contaminant Cohort Study (MISA) donated a blood and urine sample at three visits during their pregnancy and postpartum period (in second trimester, 3 days and 6 weeks after delivery. N=197). Women were assigned to iodine status groups according to urine iodine concentrations (UICs) in second trimester and mixed effects linear models were used to investigate potential associations between iodine status and repeated measurements of thyroid-stimulating hormone (TSH), thyroid hormones (THs), TH-binding proteins and thyroid peroxidase antibodies. Associations between maternal iodine status and TSH in heel prick samples from the infants were investigated with linear regression.

RESULTS

Median UIC in second trimester was 84 μg/l (range 18-522) and 80% had UIC below recommended level (<150 μg/l). Iodine-deficient women had higher concentrations of T3, FT3 and FT4 (estimated differences (confidence intervals) of 0.10 nmol/l (0.01, 0.17), 0.16 pmol/l (0.05, 0.26) and 0.45 pmol/l (0.10, 0.78), respectively) compared with iodine-sufficient women. The concentrations varied within normal reference ranges, but the majority of women with subclinical hypothyroidism were iodine deficient. Maternal iodine status did not influence infant TSH concentrations.

CONCLUSIONS

This study indicate iodine deficiency among pregnant women in Norway. Iodine status during pregnancy influences maternal thyroid homeostasis and is therefore a risk factor for foetal and infant development.

Patients with subclinical hypothyroidism before 20 weeks of pregnancy have a higher risk of miscarriage: A systematic review and meta-analysis

Objective

To evaluate the relationship between subclinical hypothyroidism (SCH) and the risk of miscarriage before 20 weeks of pregnancy.

Methods

Literature databases were searched, including the PubMed, Web of Science, Embase and Cochrane databases, from January 1, 1980, to December 31, 2015. The following search terms were used: subclinical hypothyroidism, hypothyroidism, thyroid dysfunction, thyroid hypofunction, subclinical thyroid disease, thyroid dysfunction, pregnancy loss, abortion and miscarriage. Studies comparing the prevalence of miscarriage in pregnant women with SCH with those who were euthyroid were selected. From the studies matched, the relative risk (RR) and corresponding 95% confidence interval (95% CI) were calculated to yield outcomes. All the statistical analyses were performed using Review Manager (Revman) Version 5.3 and Stata Version 12.0 software. The publication bias of the studies was assessed by forest plot and Begg’s test, while the stability of the results was evaluated by sensitivity analysis.

Results

Nine articles satisfying the inclusion criteria were analysed. Compared to euthyroid pregnant women, patients with non-treated SCH had a higher prevalence of miscarriage (RR = 1.90, 95% CI1.59–2.27, P<0.01). Additionally, SCH patients in the international diagnostic criteria group were more likely to suffer miscarriages than those in the ATA diagnostic criteria group (χ² = 11.493, P<0.01). Moreover, there was no difference between patients with treated SCH and euthyroid women (RR = 1.14, 95% CI0.82–1.58, P = 0.43). Compared to isolated SCH women, the miscarriage risk of SCH patients with thyroid autoimmunity (TAI) was obviously higher (RR = 2.47, 95% CI1.77–3.45, P<0.01), and isolated SCH patients also had a higher prevalence of miscarriages than euthyroid women (RR = 1.45, 95% CI1.07–1.96, P = 0.02).A heterogeneity test, forest plot and Begg’s test suggested that there was no significant heterogeneity or publication bias among the included articles, while the result of sensitivity analysis showed that our study exhibited high stability.

Conclusion

SCH is a risk factor for miscarriage in women before 20 weeks of pregnancy, and early treatments can reduce the miscarriage rate. Regardless of the diagnostic criteria used, the miscarriage rate increased as long as a pregnant woman was confirmed to have SCH. The results show that the omission diagnostic rate may increase when the ATA diagnostic criteria are used. In addition, SCH patients with TAI have a higher prevalence of miscarriage, while isolated SCH patients also have a higher miscarriage rate than euthyroid women. Thus, we recommend early treatments to avoid adverse pregnancy outcomes and complications.

Thyroglobulin as a Functional Biomarker of Iodine Status in a Cohort Study of Pregnant Women in the United Kingdom

BACKGROUND

Though iodine deficiency in pregnancy is a matter of public-health concern, a functional measure of iodine status is lacking. The thyroid-specific protein thyroglobulin (Tg), which reflects thyroid size, has shown promise as a functional measure in studies of children and adults, but data in pregnancy are sparse. In a cohort of mildly to moderately iodine-deficient pregnant women, this study aimed to explore whether serum Tg is a sensitive functional biomarker of iodine status and to examine longitudinal change in Tg with gestational age.

METHOD

A total of 230 pregnant women were recruited at an antenatal clinic at 12 weeks of gestation to the Selenium in PRegnancy INTervention study, in Oxford, United Kingdom. Repeated measures of urinary iodine-to-creatinine ratio, serum thyrotropin (TSH), and Tg at 12, 20, and 35 weeks of gestation were made. Women were dichotomized by their iodine-to-creatinine ratio (<150 or ≥150 μg/g) to group them broadly as iodine deficient or iodine sufficient. Women with thyroid antibodies were excluded; data and samples were available for 191 women.

RESULTS

Median Tg concentrations were 21, 19, and 23 μg/L in the first, second, and third trimesters, respectively. In a linear mixed model, controlling for confounders, Tg was higher in the <150 μg/g group than it was in the ≥150 μg/g group (p < 0.001) but there was no difference in TSH (p = 0.27). Gestational week modified the effect of iodine status on TSH (p = 0.01) and Tg (p = 0.012); Tg did not increase with gestational week in the ≥150 μg/g group, but it did in the <150 μg/g group, and TSH increased more steeply in the <150 μg/g group.

CONCLUSIONS

Low iodine status (<150 μg/g) in pregnancy is associated with higher serum Tg, suggesting that the thyroid is hyperstimulated by iodine deficiency, which causes it to enlarge. Tg is a more sensitive biomarker of iodine status in pregnancy than is TSH.

2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum

BACKGROUND

Thyroid disease in pregnancy is a common clinical problem. Since the guidelines for the management of these disorders by the American Thyroid Association (ATA) were first published in 2011, significant clinical and scientific advances have occurred in the field. The aim of these guidelines is to inform clinicians, patients, researchers, and health policy makers on published evidence relating to the diagnosis and management of thyroid disease in women during pregnancy, preconception, and the postpartum period.

METHODS

The specific clinical questions addressed in these guidelines were based on prior versions of the guidelines, stakeholder input, and input of task force members. Task force panel members were educated on knowledge synthesis methods, including electronic database searching, review and selection of relevant citations, and critical appraisal of selected studies. Published English language articles were eligible for inclusion. The American College of Physicians Guideline Grading System was used for critical appraisal of evidence and grading strength of recommendations. The guideline task force had complete editorial independence from the ATA. Competing interests of guideline task force members were regularly updated, managed, and communicated to the ATA and task force members.

RESULTS

The revised guidelines for the management of thyroid disease in pregnancy include recommendations regarding the interpretation of thyroid function tests in pregnancy, iodine nutrition, thyroid autoantibodies and pregnancy complications, thyroid considerations in infertile women, hypothyroidism in pregnancy, thyrotoxicosis in pregnancy, thyroid nodules and cancer in pregnant women, fetal and neonatal considerations, thyroid disease and lactation, screening for thyroid dysfunction in pregnancy, and directions for future research.

CONCLUSIONS

We have developed evidence-based recommendations to inform clinical decision-making in the management of thyroid disease in pregnant and postpartum women. While all care must be individualized, such recommendations provide, in our opinion, optimal care paradigms for patients with these disorders.

Thyroid hormone treatment among pregnant women with subclinical hypothyroidism: US national assessment

OBJECTIVE

 To estimate the effectiveness and safety of thyroid hormone treatment among pregnant women with subclinical hypothyroidism.

DESIGN

 Retrospective cohort study.

SETTING

 Large US administrative database between 1 January 2010 and 31 December 2014.

PARTICIPANTS

 5405 pregnant women with subclinical hypothyroidism, defined as untreated thyroid stimulating hormone (TSH) concentration 2.5-10 mIU/L.

EXPOSURE

 Thyroid hormone therapy.

MAIN OUTCOME MEASURE

 Pregnancy loss and other pre-specified maternal and fetal pregnancy related adverse outcomes.

RESULTS

 Among 5405 pregnant women with subclinical hypothyroidism, 843 with a mean pre-treatment TSH concentration of 4.8 (SD 1.7) mIU/L were treated with thyroid hormone and 4562 with a mean baseline TSH concentration of 3.3 (SD 0.9) mIU/L were not treated (P<0.01). Pregnancy loss was significantly less common among treated women (n=89; 10.6%) than among untreated women (n=614; 13.5%) (P<0.01). Compared with the untreated group, treated women had lower adjusted odds of pregnancy loss (odds ratio 0.62, 95% confidence interval 0.48 to 0.82) but higher odds of preterm delivery (1.60, 1.14 to 2.24), gestational diabetes (1.37, 1.05 to 1.79), and pre-eclampsia (1.61, 1.10 to 2.37); other pregnancy related adverse outcomes were similar between the two groups. The adjusted odds of pregnancy loss were lower in treated women than in untreated women if their pre-treatment TSH concentration was 4.1-10 mIU/L (odds ratio 0.45, 0.30 to 0.65) but not if it was 2.5-4.0 mIU/L (0.91, 0.65 to 1.23) (P<0.01).

CONCLUSION

 Thyroid hormone treatment was associated with decreased risk of pregnancy loss among women with subclinical hypothyroidism, especially those with pre-treatment TSH concentrations of 4.1-10 mIU/L. However, the increased risk of other pregnancy related adverse outcomes calls for additional studies evaluating the safety of thyroid hormone treatment in this patient population.

Neonatal thyrotropin concentration and iodine nutrition status of mothers: a systematic review and meta-analysis

BACKGROUND

Low maternal iodine intake disturbs the thyroid function of neonates transiently or permanently.

OBJECTIVE

To our knowledge, we conducted one of the first systematic reviews and meta-analyses aimed at exploring the association of neonatal thyrotropin concentrations and iodine status of mothers during pregnancy and early postpartum periods.

DESIGN

Data were collected through literature searches for studies published between 1969 and 2015 with the use of electronic databases. Mean or median maternal urinary iodine and neonatal thyrotropin concentrations, along with other relevant data, were extracted from eligible studies. The quality and risk of bias of each study was assessed.

RESULTS

A random-effects model was used for the analysis. Of 110 studies identified, 25 trials were shown to be eligible for inclusion in the meta-analysis. Mean (95% CI) thyrotropin concentrations of neonates born to mothers with iodine deficiency were higher than in neonates born to mothers with iodine sufficiency during pregnancy in both heel blood samples [1.79 mIU/L (95% CI: 1.61, 1.97 mIU/L) compared with 1.75 mIU/L (95% CI: 1.68, 1.82 mIU/L), respectively] and cord blood samples [11.91 mIU/L (95% CI: 6.67, 17.14 mIU/L) compared with 6.15 mIU/L (95% CI: 4.30, 8.01 mIU/L), respectively]. There were no significant differences in neonatal thyrotropin concentrations of heel samples between mothers with iodine deficiency and those with sufficiency during the early postpartum period; however, the values of thyrotropin in cord samples of neonates born to mothers with iodine deficiency were significantly higher than in neonates born to mothers with iodine sufficiency [11.62 mIU/L (95% CI: 10.47, 12.77 mIU/L) compared with 7.40 mIU/L (95% CI: 6.21, 8.59 mIU/L)].

CONCLUSION

Our findings reveal that, compared with heel blood samples, neonatal thyrotropin in samples collected from the cord are more sensitive to the iodine status of mothers; however, further investigations are required in this regard.

Subclinical hypothyroidism causing hypertension in pregnancy

This is a case of a 25-year-old primigravida who was referred to the hypertension specialist for elevated blood pressures. The patient had an elevated thyroid-stimulating hormone with normal free thyroxine (T4) levels and was positive for thyroid peroxidase antibodies resulting in a diagnosis of subclinical hypothyroidism. The patient was successfully treated with levothyroxine which normalized the blood pressure without the need for antihypertensive treatment. This case illustrates a cause of secondary hypertension that is not always considered in the differential diagnosis of a patient with hypertension in pregnancy.

Adequate iodine levels in healthy pregnant women. A cross-sectional survey of dietary intake in Turkey

Objectives:

To assess current iodine levels and related factors among healthy pregnant women.

Methods:

In this cross-sectional, hospital-based study, healthy pregnant women (n=135) were scanned for thyroid volume, provided urine samples for urinary iodine concentration and completed a questionnaire including sociodemographic characteristics and dietary habits targeted for iodine consumption at the Department of Obstetrics and Gynecology, School of Medicine, Muğla Sıtkı Koçman University, Muğla, Turkey, between August 2014 and February 2015. Sociodemographic data were analyzed by simple descriptive statistics.

Results:

Median urinary iodine concentration was 222.0 µg/L, indicating adequate iodine intake during pregnancy. According to World Health Organization (WHO) criteria, 28.1% of subjects had iodine deficiency, 34.1% had adequate iodine intake, 34.8% had more than adequate iodine intake, and 3.0% had excessive iodine intake during pregnancy. Education level, higher monthly income, current employment, consuming iodized salt, and adding salt to food during, or after cooking were associated with higher urinary iodine concentration.

Conclusion:

Iodine status of healthy pregnant women was adequate, although the percentage of women with more than adequate iodine intake was higher than the reported literature.

The Urine Iodine to Creatinine as an Optimal Index of Iodine During Pregnancy in an Iodine Adequate Area in China

CONTEXT

Iodine nutrition is a global event, especially for pregnant women.

OBJECTIVE

To develop applicable index of iodine intake for population during pregnancy.

DESIGN, SETTING, AND PARTICIPANTS

From 2012 to 2014, pregnant women at less than 8 weeks of gestation (n = 222) and reproductive-age women (n = 827) participated in this study. The pregnant women were evaluated at follow-up visits at 8, 12, 16, 20, 28, and 36 weeks of gestation and 3 and 6 months postpartum.

MAIN OUTCOME MEASURES

Twenty-four-hour urine samples were collected at weeks 8 of gestation. Urine iodine (UI) and creatinine (Cr) and serum thyroglobulin were measured in all of the subjects. Circulatory iodine was measured using inductively coupled plasma-mass spectrometry at 8, 20, and 36 weeks of gestation and 6 months postpartum.

RESULTS

The median UI concentration decreased from 183.6 to 104.2 μg/L during pregnancy. The serum iodine (SI) changes were similar to the UI to creatinine ratio (UI/Cr). The SI level was lowest at the eighth week of gestation (60.5 μg/L), which rose significantly until 20 weeks (106.5 μg/L) and then began to decline (36 wk, 84.7 μg/L). The 24-hour UI excretion measurement was regarded as the gold standard. The area under the receiver-operating characteristic curve for UI/Cr was 0.92 for iodine deficiency diagnoses and 0.78 for SI. The area for SI was 0.82 for excessive iodine diagnoses and 0.75 for UI/Cr. The areas under these curves were significantly different (P < .001). The areas under the receiver-operating characteristic curve for UI were 0.61 (P = .11) and 0.65 (P = .08) for iodine deficiency and excessive iodine diagnoses, respectively. Additionally, for thyroglobulin, these values were 0.54 (P = .53) and 0.53 (P = .74), respectively.

CONCLUSIONS

Iodine intake, as assessed by spot UI concentration in pregnant women, is inaccurate and increases the prevalence of iodine deficiency. The UI/Cr better reflects the 24-hour iodine excretion and circulating iodine levels during pregnancy and the postpartum period.

Screening of subclinical hypothyroidism during gestational diabetes in Pakistani population

OBJECTIVE

The increased prevalence of adverse effects of altered thyroid functions in pregnancy inspired us to study the frequency of subclinical hypothyroidism (SCH) and the relationship with glycaemic control and foetal weight in pregnant females with and without gestational diabetes mellitus (GDM) in Pakistani population.

PATIENTS AND METHODS

Five hundred and eight pregnant females were enrolled and grouped as per the International Diabetes Association criteria into GDM (n = 208) and healthy control (n = 300). Random blood glucose (RBG), thyroid function tests, anthropometric analysis and foetal ultra sound scans were performed on all study subjects. Data were analysed using Mann-Whitney U test and Chi-square test wherever applicable. Spearman correlation and multiple regression analysis were performed. p values of <0.05 was considered significant.

RESULTS

A total of 61.5% GDM subjects depicted SCH with normal circulating T4 and T3 versus 6.0% healthy controls (p-value < 0.001). Moreover, TSH remained independently associated with RBG (r = 0.109; p < 0.05), poor glycaemic control (r = 0.227; p < 0.001) and negatively associated with foetal growth (r = -0.206; p < 0.001).

CONCLUSION

The detection of high TSH with normal T3 and T4 in females with GDM strongly emphasises the need of thyroid screening as a routine in all antenatal clinics.

The importance of iodine in public health

Iodine (I) deficiency has been known for more than a century and is known to cause cretinism at the extreme end of the spectrum but also, importantly, impaired development and neurocognition in areas of mild deficiency. The WHO has indicated that median urinary iodine of 100-199 μg/l in a population is regarded as indicative of an adequate iodine intake. The understanding of the spectrum of iodine deficiency disorders led to the formation of The International Council for the Control of Iodine Deficiency Disorders which has promulgated the use of household iodized salt and the use of such salt in food processing and manufacture. Iodine deficiency is particularly important in pregnancy as the fetus relies on maternal thyroxine (T4) exclusively during the first 14 weeks and also throughout gestation. As this hormone is critical to brain and nervous system maturation, low maternal T4 results in low child intelligence quotient. The recommendation for I intake in pregnancy is 250 μg/day to prevent fetal and child brain function impairment. During the past 25 years, the number of countries with I deficiency has reduced to 32; these still include many European developed countries. Sustainability of adequate iodine status must be achieved by continuous monitoring and where this has not been performed I deficiency has often recurred. More randomized controlled trials of iodine supplementation in pregnancy are required in mild iodine-deficient areas to inform public health strategy and subsequent government action on suitable provision of iodine to the population at risk.

Gestational changes in iodine status in a cohort study of pregnant women from the United Kingdom: season as an effect modifier

BACKGROUND

Iodine is required throughout pregnancy for thyroid hormone production, which is essential for fetal brain development. Studies of iodine status in pregnant women from the United Kingdom (UK) have focused on early gestation (<16 wk). Data on the effect of advancing gestation on urinary iodine excretion are conflicting, with suggestions of both an increase and a decrease.

OBJECTIVES

The aims were to evaluate iodine status in a cohort of UK pregnant women and to explore how it changes throughout gestation.

DESIGN

We used samples and data from 230 UK pregnant women who were recruited to the Selenium in PRegnancy INTervention study. Iodine concentration was measured in spot-urine samples that were collected at ∼12, 20, and 35 wk of gestation; creatinine concentration was also measured to correct for urine dilution. A linear mixed model was used to explore the effect of gestational week on iodine-to-creatinine ratio, with change in season, body mass index, daily milk intake, and maternal age controlled for.

RESULTS

The median urinary iodine concentration from urine samples collected at all time points (n = 662) was 56.8 μg/L, and the iodine-to-creatinine ratio was 116 μg/g, thus classifying this cohort as mildly-to-moderately iodine deficient. The median iodine-to-creatinine ratios at 12, 20, and 35 wk were 102.5, 120.0, and 126.0 μg/g, respectively. Only 3% of women were taking iodine-containing prenatal supplements. The iodine-to-creatinine ratio increased with advancing gestation, and there was a significant interaction between gestational week and season (P = 0.026). For a 1-wk increase in gestation, the iodine-to-creatinine ratio increased by a factor of 1.05 (95% CI: 1.02, 1.08) in winter and by a factor of 1.04 (95% CI: 1.00, 1.08) in summer.

CONCLUSIONS

This group of UK pregnant women was mildly-to-moderately iodine deficient at all trimesters, which is of public health concern. The finding that the iodine-to-creatinine ratio increased over the course of gestation may not be generalizable to populations with different iodine status from ours and merits further investigation. This trial was registered at www.isrctn.com as ISRCTN37927591.

Urinary iodine level and its determinants in pregnant women of Shanghai, China

It is known that iodine deficiency during pregnancy can interfere with normal fetal growth and development. However, iodine levels of pregnant women in Shanghai, China, and factors that could influence its levels remain unclear. A total of 916 pregnant women were selected from the Maternal and Child Care Service Centre of Minhang District in Shanghai. Morning urinary iodine (UI) and iodine content of salt from the participants' home were measured, and UI concentration was adjusted by creatinine concentrations. Serum tri-iodothyronine, thyroxin, free tri-iodothyronine, free thyroxine and thyroid-stimulating hormone were tested in the second trimester of pregnancy by time-resolved fluoroimmunoassay. The median levels of UI in pregnant women were 156·3, 176·9 and 175·1 μg/g creatinine in the first, second and third trimesters of pregnancy, respectively. The prevalence of UI deficiency (UI < 150 μg/g creatinine) was 48·3, 34·2 and 36·2 % in the three trimesters of pregnancy, respectively. Factors that significantly influenced the UI levels include the following: iodine content of household salt; age; occupation; multivitamin supplement with iodine; seaweed intakes. Furthermore, UI and iodine content of salt were moderately correlated (r0·406,P< 0·001). In addition, there was no significant association between UI and thyroid hormone levels. The present study showed a high prevalence of UI deficiency in pregnant women in Shanghai, especially during the first trimester of pregnancy. Both iodine content of household salt and multivitamin supplement with iodine are the main determinants of UI levels in Shanghai.

Normal intellectual development in children born from women with hypothyroxinemia during their pregnancy

Proper maternal thyroid function is known to be essential for neural differentiation and migration in the fetus during the first half of pregnancy. The objectives of this study were to assess the relationship between thyroxin levels, in pregnant women with no thyroid disease and the intellectual development of their offspring in a non-iodine-deficient area, and to know specifically whether or not isolated hypothyroxinemia during pregnancy was associated with a lower intelligence in the offspring. Previously we had publicated values TSH, FT4, free T3 (FT3), anti-thyroid peroxidase antibodies (TPO Abs) and urinary iodine concentration (UIC) in 1322 pregnant women in our hospital area. Now we presented results of intelligence quotient in children born from these pregnancies. We assessed 455 children at one year of age using Brunet-Lezine scale. Of these, 289 children were evaluated again at 6-8 years of age using the WISC-IV. From the total group of children recruited, we established as control subgroup, children born of rigorously normal pregnancies (women with UIC > 150 μg/L, FT4>10th percentile and TPO-Ab negative in both trimesters). The remaining children were divided into two subgroups: those born to mothers with FT4 below the 10th percentile and the rest. No correlation was found between FT4 maternal levels, in either of trimesters studied, and the intellectual scores of offspring. No differences were found in intellectual scores comparing children born to mothers with hypothyroxinemia and those whose mothers were euthyroxinemic in both trimesters, or with the control subgroup. As conclusions we did not find any association between the levels of maternal FT4 during pregnancy and the subsequent intellectual development the offspring from these pregnancies. We attribute this result to the fact that all the pregnant women included had normal thyroid function.

Iodine intake and status of UK women of childbearing age recruited at the University of Surrey in the winter

As intra-thyroidal iodine stores should be maximised before conception to facilitate the increased thyroid hormone production during pregnancy, women who are planning to become pregnant should ideally consume 150 μg iodine/d (US RDA). As few UK data exist for this population group, a cross-sectional study was carried out at the University of Surrey to assess the iodine intake and status of women of childbearing age. Total iodine excretion was measured from 24 h urine samples in fifty-seven women; iodine intake was estimated by assuming that 90 % of ingested iodine was excreted. The average iodine intake was also estimated from 48 h food diaries that the participants completed. The median urinary iodine concentration value (63·1 μg/l) indicated the group to be mildly iodine deficient by WHO criteria. By contrast, the median 24 h urinary iodine excretion value (149·8 μg/24 h) indicated a relatively low risk of iodine deficiency. The median estimated iodine intake, extrapolated from urinary excretion, was 167 μg/d, whereas it was lower, at 123 μg/d, when estimated from the 48 h food diaries. Iodine intake estimated from the food diaries and 24 h urinary iodine excretion were strongly correlated (r 0·75, P< 0·001). The intake of milk, eggs and dairy products was positively associated with iodine status. The iodine status of this UK cohort is probably a best-case scenario as the women were mostly nutrition students and were recruited in the winter when milk-iodine content is at its highest; further study in more representative cohorts of UK women is required. The present study highlights the need for revised cut-off values for iodine deficiency that are method- and age group-specific.

[Thyroid dysfunction during pregnancy]

Recent clinical practice guidelines on thyroid dysfunction and pregnancy have changed health care provided to pregnant women, although their recommendations are under constant revision. Trimester- and area-specific reference ranges for serum thyroid-stimulating hormone are required for proper diagnosis of hypothyroidism and hyperthyroidism. There is no doubt on the need of therapy for overt hypothyroidism, while therapy for subclinical hypothyroidism is controversial. Further research is needed to settle adverse effects of isolated hypothyroxinemia and thyroid autoimmunity. Differentiation between hyperthyroidism due to Graves' disease and the usually self-limited gestational transient thyrotoxicosis is critical. It is also important to recognize risk factors for postpartum thyroiditis. Supplementation with iodine is recommended to maintain adequate iodine nutrition during pregnancy and avoid serious consequences in offspring. Controversy remains about universal screening for thyroid disease during pregnancy or case-finding in high-risk women. Opinions of some scientific societies and recent cost-benefit studies favour universal screening. Randomized controlled studies currently under development should reduce the uncertainties that still remain in this area.

2014 European thyroid association guidelines for the management of subclinical hypothyroidism in pregnancy and in children

This guideline has been produced as the official statement of the European Thyroid Association guideline committee. Subclinical hypothyroidism (SCH) in pregnancy is defined as a thyroid-stimulating hormone (TSH) level above the pregnancy-related reference range with a normal serum thyroxine concentration. Isolated hypothyroxinaemia (defined as a thyroxine level below the 2.5th centile of the pregnancy-related reference range with a normal TSH level) is also recognized in pregnancy. In the majority of SCH the cause is autoimmune thyroiditis but may also be due to iodine deficiency. The cause of isolated hypothyroxinaemia is usually not apparent, but iodine deficiency may be a factor. SCH and isolated hypothyroxinaemia are both associated with adverse obstetric outcomes. Levothyroxine therapy may ameliorate some of these with SCH but not in isolated hypothyroxinaemia. SCH and isolated hypothyroxinaemia are both associated with neuro-intellectual impairment of the child, but there is no evidence that maternal levothyroxine therapy improves this outcome. Targeted antenatal screening for thyroid function will miss a substantial percentage of women with thyroid dysfunction. In children SCH (serum TSH concentration >5.5-10 mU/l) normalizes in >70% and persists in the majority of the remaining patients over the subsequent 5 years, but rarely worsens. There is a lack of studies examining the impact of SCH on the neuropsychological development of children under the age of 3 years. In older children, the evidence for an association between SCH and impaired neuropsychological development is inconsistent. Good quality studies examining the effect of treatment of SCH in children are lacking.