An assessment of the iodine status and the correlation between iodine nutrition and thyroid function during pregnancy in an iodine sufficient area

Association Between Maternal Characteristics and the Risk of Isolated Maternal Hypothyroxinemia

OBJECTIVE

We aimed to determine the association between maternal characteristics and isolated maternal hypothyroxinemia (IMH).

METHODS

Pregnancies registered at Shanghai First Maternity and Infant Hospital between January 2014 and September 2020 were included in this cross-sectional study. IMH was defined as free thyroxine (FT4) levels below the 10th percentile with TSH within the normal reference range. Multivariate logistic regression models were used to identify potential risk factors for IMH, including demographic information, anthropometric measurements and nutritional status.

RESULTS

A total of 54586 singleton pregnancies were included, involving 6084 women with IMH and 48502 euthyroid women. Multivariate logistic regression analyses showed that the variables for women with ages ≥35 (adjusted OR = 1.30, 95% CI:1.20-1.40), non-local residence (adjusted OR = 1.16, 95% CI:1.09-1.23), multiparas (adjusted OR = 1.11, 95% CI:1.03-1.21), pre-pregnancy overweight (adjusted OR = 1.37, 95% CI:1.27-1.49) or obesity (adjusted OR = 1.35, 95% CI:1.18-1.54), and iron deficiency (adjusted OR = 1.27, 95% CI:1.20-1.35) were independent risk factors for IMH in the overall study population, which were identical to those in the first trimester subgroup.

CONCLUSIONS

Maternal characteristics were associated with the onset of IMH. Maternal age, residence of origin, parity, pre-pregnancy body mass index (BMI) and iron status should be comprehensively considered to evaluate the risk of IMH, according to which obstetricians could determine an optimal assessment time for thyroid function.

Do maternal urinary iodine concentration or thyroid hormones within the normal range during pregnancy affect growth parameters at birth? A systematic review and meta-analysis

CONTEXT

Iodine, an essential constituent of thyroid hormones, is required for proper growth and development.

OBJECTIVE

To investigate whether growth parameters at birth are associated with maternal urinary iodine concentration (UIC) or normal ranges of thyroid hormones during pregnancy.

DATA SOURCES

Using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, electronic databases (namely, MEDLINE, Web of Science, the Cochrane Library, Scopus, and Google Scholar) were searched between January 1988 and November 2018 to identify relevant articles.

DATA EXTRACTION

Data from the studies included were independently extracted by 2 investigators using standardized forms developed for this review.

DATA ANALYSIS

The pooled mean birth weight, length, and head circumference values, and 95% confidence intervals were estimated in newborns born to women with UIC < 150 and UIC ≥150 μg/L during pregnancy. Possible linear or nonlinear associations between maternal UIC and the aforementioned anthropometric measures were evaluated. A narrative synthesis of the data was performed for thyroid hormones with levels within the normal range.

RESULTS

Of the 123 studies identified, 11 were eligible for inclusion in the meta-analysis. The pooled mean birth weight, length, and head circumference in newborns whose mothers had UIC < 150 μg/L vs UIC ≥150 μg/L were 2898 g vs 2900 g (P = 0.970), 49.6 cm vs 49.4 cm (P = 0.880), and 34.0 cm vs 34.1 cm (P = 0.933), respectively. Dose-response meta-analyses revealed no significant linear or nonlinear associations between maternal UIC during pregnancy and anthropometric measures at birth. Among the different thyroid function parameters evaluated, high-normal values of maternal free thyroxine and thyrotropin during pregnancy were inversely associated with neonatal birth weight.

CONCLUSION

This systematic review showed that birth weight may be affected by even mild variations in the normal concentrations of maternal thyroid hormones. However, in the current meta-analysis, birth anthropometric measures were not associated with maternal UIC during pregnancy.

Reference Values of Thyroid Hormones During the First Trimester of Pregnancy in Valencian Community (Spain) and Their Relationship with Iodine Intake

Thyroid hormones require special monitoring during the first trimester of gestation. Local reference values should be applied if available, especially in iodine-deficient areas, as generalized iodine supplementation is controversial. The aim of the present study was to establish thyroid stimulating hormone (TSH) and free thyroxine (FT4) reference values in the first trimester of gestation in the Valencian community (Spain) and relate them to iodine intake. A total of 261 healthy pregnant women participated in the study. The calculated reference values were 0.128-4.455 mIU/L for TSH and 0.9-1.592 ng/dL for FT4. The upper TSH reference value for pregnant women in the first trimester in our environment was similar to the latest American Thyroid Association (ATA) recommendation (4 mIU/L). The mean TSH value was significantly lower in smokers, and there were no significant differences when analyzing the influence of iodine supplementation, although the low duration of supplement intake needs to be taken into consideration. Ioduria levels (median 57 µg/L) confirmed iodine deficiency. We found statistically significant differences in ioduria levels among patients who consumed iodized salt and iodine supplements and those who did not. It is essential to focus on recommending adequate consumption of iodized salt and iodine supplements prior to gestation and at least during the first trimester to avoid possible maternal thyroid dysfunction and perinatal complications.

High prevalence of TPO-Abs and subclinical hypothyroidism in iodine-sufficient pregnant women in Northern Algeria

BACKGROUND

Iodine is a trace element whose adequate intakes are essential during gestation to promote the correct growth and development of the fetus. Historically, endemic goiter and cretinism affected northern regions of Algeria, and iodized salt was introduced in 1990. However, there has been no national study of iodine nutrition in Algeria since 1994. The aim of this study was to assess the iodine status and thyroid function of women of reproductive age (WRA) and pregnant women (PW) in northern Algeria.

METHODS

Healthy WRA and PW were recruited from an urban area (Algiers) and healthy WRA from a rural area (Tizi-Ouzou). Spot urine and venous blood samples were collected to assess iodine status (urinary iodine concentration, UIC) and serum thyroid hormones (TSH, FT4), thyroglobulin (Tg), and anti-thyroid peroxidase antibodies (TPO-Ab) concentrations.

RESULTS

The median UIC in WRA was 256 μg/L (IQR: 166-354 μg/L; n = 151) in Algiers and 253 μg/L (167-341 μg/L; n = 150) in Tizi-Ouzou. The median UIC for the PW in Algiers was 233 μg/L (IQR: 157-326 μg/L; n = 173).Thirty-five percent of WRA and 30% of PW had an UIC > 300 μg/L. Median TSH, FT4 and Tg concentrations were within reference ranges in all groups of women. Among PW, 72.7%, 75.4% and 75.5% in the first, second and third trimester were TPO-Ab+. Among TPO-Ab + PW in the first, second and third trimesters, 18.7%, 13% and 10.3% had subclinical hypothyroidism.

CONCLUSION

In northern Algeria, median UICs in PW indicate iodine sufficiency, and in WRA indicate more than adequate intakes. About 75% of PW are TPO-Ab + and the prevalence of subclinical hypothyroidism is high. Monitoring and surveillance of iodine fortification programs is vital to avoid both iodine deficiency and excess. There is an urgent need for a comprehensive national iodine status survey including school-age children and other vulnerable population groups in Algeria.

Isolated Hypothyroxinemia in Iranian Pregnant Women, the Role of Iodine Deficiency: A Population-Based Cross-Sectional Study

Background: Thyroid disorders such as subclinical hypothyroidism and isolated maternal hypothyroxinemia are understudied in pregnant women, despite their possible adverse effects on the health of mother and child. Also, the role of iodine deficiency in developing such disorders has not yet been fully understood. Methods: The present national population-based cross-sectional study was conducted on 1080 randomly recruited pregnant women, aged 20-40 from 12 provinces of Iran from 2013 to 2014. Serum concentrations of thyrotropin, T4, thyroid peroxidase antibody (TPOAb), and triiodothyronine (T3) resin uptake values were measured in fasting blood samples, and urinary iodine concentration (UIC) was measured in three separate urine samples. Multinomial logistic regression was run to analyze the possible risk factors regarding thyroid disorders. To clarify the role of iodine in thyroid status specifically, the determinants of UIC and its correlations with thyroid function tests were investigated independently and through subgroup analysis. Results: Isolated hypothyroxinemia was the most common thyroid disorder (9.9%), followed by subclinical hypothyroidism (8%). In comparison to euthyroid pregnant women, isolated hypothyroxinemia was more likely in pregnant women older than 30 years (odds ratio [OR] = 1.6), in the second and the third trimesters (OR = 2.62 and 2.12 respectively), with history of multiparity (OR = 1.72), residing in rural areas (OR = 1.57) and in the capital province of the country (OR = 3.3). Subclinical hypothyroidism was more likely in TPOAb positive pregnant women (OR = 2.56). All the mentioned ORs were statistically significant (p < 0.05). The UIC did not correlate significantly with any of the thyroid function tests in the study population. Subgroup analysis showed a significant correlation between UIC and T4 in pregnant women with subclinical hypothyroidism (p < 0.05). Conclusion: Isolated maternal hypothyroxinemia was the most prevalent thyroid disorder in Iranian pregnant women and its associated risk factors were identified. Although the calculated prevalence of thyroid disorders was expected in a moderately iodine deficient setting, no correlations between UICs and thyroid function tests were found at the individual level. The contribution of iodine deficiency to thyroid condition for each pregnant woman may be more evident in pregnant women with certain thyroid disorders or those with long-term iodine deficiency.

Variation of iodine status during pregnancy and its associations with thyroid function in women from Rio de Janeiro, Brazil

OBJECTIVE

To assess iodine status and its effects on maternal thyroid function throughout pregnancy.

DESIGN

In the present prospective cohort study, three urinary samples were requested for urinary iodine concentration (UIC) determinations in both the first and third gestational trimesters. Serum thyrotropin (TSH) and free thyroxine (FT4) were analysed in both trimesters and thyroid antibodies were assessed once.

SETTING

Rio de Janeiro, Brazil.ParticipantsFirst-trimester pregnant women (n 243), of whom 100 were re-evaluated during the third trimester.

RESULTS

Iodine sufficiency was found in the studied population (median UIC=216·7 µg/l). The first- and third-trimester median UIC was 221·0 and 208·0 µg/l, respectively. TSH levels (mean (sd)) were higher in the third trimester (1·08 (0·67) v. 1·67 (0·86) mIU/l; P&lt;0·001), while FT4 levels decreased significantly (1·18 (0·16) v. 0·88 (0·12) ng/dl; P&lt;0·001), regardless the presence of iodine deficiency (UIC&lt;150 µg/l) or circulating thyroid antibodies. UIC correlated (β; 95% CI) independently and negatively with age (-0·43; -0·71, -0·17) and positively with multiparity (0·15; 0·02, 0·28) and BMI (0·25; 0·00, 0·50). Furthermore, median UIC per pregnant woman tended to correlate positively with TSH (0·07; -0·01, 0·14). Women with median UIC≥250 µg/l and at least one sample ≥500 µg/l throughout pregnancy had a higher risk of subclinical hypothyroidism (OR=6·6; 95% CI 1·2, 37·4).

CONCLUSIONS

In this cohort with adequate iodine status during pregnancy, excessive UIC was associated with an increased risk of subclinical hypothyroidism.

Iodine Nutrition During Pregnancy: Past, Present, and Future

Iodine is a trace element that is important for the synthesis of thyroid hormones. During pregnancy, iodine requirements are increased by approximately 50% because of physiological changes. Adequate iodine status in pregnancy is crucial for maternal health and fetal growth. The World Health Organization (WHO) recommends a daily intake of 250 μg iodine for pregnant women to maintain adequate iodine status. Severe iodine deficiency during pregnancy can result in a series of detrimental effects on maternal and fetal health including hypothyroidism, goiter, stillbirth, abortion, increased neonatal mortality, neurological damage, and intellectual impairment. Correction of severe iodine deficiency can reduce the risk of adverse impacts. However, the influences of mild-to-moderate maternal iodine deficiency on fetal neural development and cognitive function are less clear. The safety and efficacy of iodine supplementation in mildly-to-moderately iodine-deficient women also remain uncertain. In addition, excess iodine during pregnancy carries a risk of adverse effects, and the recommended safe upper limits of iodine intake are controversial. Effective iodine supplementation should be implemented, and routine monitoring is necessary to guarantee adequate iodine status.

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.

Can an Educational Intervention Improve Iodine Nutrition Status in Pregnant Women? A Randomized Controlled Trial

BACKGROUND

Because of their increased need for iodine, pregnant women are among the high-risk groups for iodine deficiency. The purpose of this study was to evaluate the effectiveness of an educational program on the iodine nutrition status of pregnant women.

METHODS

In this randomized controlled trial, 100 pregnant women were randomly selected from five healthcare centers in the southern region of Tehran, the capital of Iran. In the intervention group, pregnant women received a four-month educational program, which included two face-to-face educational sessions, using a researcher-designed educational pamphlet in the second and third trimesters, and two follow-up telephone calls. Knowledge, attitude, and practice (KAP) scores, urinary iodine concentration (UIC), and salt iodine content were assessed at baseline and four months after the intervention.

RESULTS

At baseline, there were significant associations between knowledge and attitude (r = 0.38, p = 0.03) between practice and UIC (r = 0.28, p = 0.01) and between UIC and iodine content of salt (r = 0.24, p = 0.009). Although a significant difference was found in mean KAP scores between the two groups after the educational intervention, scores were significantly higher in the intervention group compared with controls (p < 0.01). There were no significant differences in UIC and iodine content of salt between the two groups at follow-up.

CONCLUSIONS

Despite educational intervention increasing KAP among women regarding the importance of iodine and iodized salt consumption during pregnancy, their iodine status did not improve. Considering the main socio-environmental determinants of iodine deficiency, in particular, the monitoring of salt fortification, prescribing iodine containing supplements as well as improving health literacy in pregnant women seem essential strategies.

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.

Dried Blood Spot Thyroglobulin as a Biomarker of Iodine Status in Pregnant Women

CONTEXT

Thyroglobulin (Tg) could be a sensitive biomarker of iodine nutrition in pregnant women (PW). A dried blood spot (DBS) assay would simplify collection and transport in field studies.

OBJECTIVES

Our aims were to (1) establish and test a reference range for DBS-Tg in PW; (2) determine whether co-measurement of Tg antibodies (Abs) is necessary to define population iodine status.

DESIGN, SETTING, AND PARTICIPANTS

Standardized cross-sectional studies of 3870 PW from 11 countries. For the DBS-Tg reference range, we included TgAb-negative PW (n = 599) from 3 countries with sufficient iodine intake.

MAIN OUTCOME MEASURES

We measured the urinary iodine concentration and DBS thyroid-stimulating hormone, total thyroxin, Tg, and TgAb.

RESULTS

In the reference population, the median DBS-Tg was 9.2 μg/L (95% confidence interval, 8.7 to 9.8 μg/L) and was not significantly different among trimesters. The reference range was 0.3 to 43.5 μg/L. Over a range of iodine intake, the Tg concentrations were U-shaped. Within countries, the median DBS-Tg and the presence of elevated DBS-Tg did not differ significantly between all PW and PW who were TgAb-negative.

CONCLUSIONS

A median DBS-Tg of ∼10 μg/L with <3% of values ≥44 μg/L indicated population iodine sufficiency. Concurrent measurement of TgAb did not appear necessary to assess the population iodine status.

Iodine Status in Pregnant Women, Lactating Mothers, and Newborns in an Area with More Than Two Decades of Successful Iodine Nutrition

Pregnant women, lactating mothers, and their newborns constitute the target population for prevention and control of iodine deficiency. Hence, the aim of this study was to evaluate the iodine nutrition status among these vulnerable groups in an area with more than two decades of successful elimination of iodine deficiency. In this cross-sectional study conducted in health care centers of Tehran, 100 pregnant women and 84 lactating mothers and their newborn were randomly selected. Urinary iodine concentration and iodine content of salts were measured using the Sandell-Kolthoff and titration methods, respectively. Urinary iodine concentration <150 μg/L for pregnant women and <100 μg/L for lactating mothers and newborns was considered as iodine nutrition inadequacy, respectively. Median (interquartile range [IQR]) urinary iodine concentration (UIC) was 103 (59-155) μg/L in pregnant women, 77 (42-194) μg/L in lactating mothers, and 198 (84-260) μg/L in newborns. Median (IQR) iodine content of salt was 26 (21-30) ppm and 25 (18-28) ppm in pregnant women and lactating mothers, respectively (P = 0.462). Iodine content of salt was significantly correlated with UIC of pregnant women (r = 0.24, P = 0.019), but no correlation was found among lactating mothers (r = 0.12, P = 0.316). Neonatal UIC was significantly correlated with iodine content of salt consumed by their mothers (r = 0.49, P = 0.001). Despite suboptimal iodine status among subgroups of Tehranian pregnant and lactating women, iodine nutrition status of newborns was within optimal levels, which may be explained by a compensatory mechanism in the mammary glands.

Potentiometric measurement of urinary iodine concentration in patients with thyroid diseases with and without previous exposure to non-radioactive iodine

Extensive application of measurement of urinary iodine concentration (UIC) in several benign and malignant thyroid diseases could profit by the availability of rapid and inexpensive measuring techniques. Aim of this study was to apply a simple and inexpensive commercially available potentiometric method for the quantification of UIC based on iodine-specific ion-selective electrodes (ISE) in patients with thyroid diseases.

This retrospective study included patients with differentiated thyroid cancer (n=286) and patients with hyperthyroidism of different etiologies (n=203). Within the whole sample (n=489) 20 patients had previously (1 week–6 months) been exposed to iodine overload, either from contrast media (n=8) or amiodarone (n=12).

: In patients not exposed to iodine, the histogram showed that the distribution of UIC violated normality. The peak of the curve occurred between 5.0 μmol/L and 6.0 μmol/L. Variability was sizeable (percent coefficient of variation, %CV: 66%, 95% confidence interval: 1.48–18.72 μmol/L). The group of exposed patients could be easily distinguished from not exposed patients (median UIC: 47.5 μmol/L vs. 5.42 μmol/L). UIC was significantly correlated to urinary creatinine concentration, but normalization to urinary creatinine increased the inter-subject variability of UIC (%CV=96% vs. 66%). In test-retest studies (n=25) the intra-class correlation coefficient was 0.73 for UIC, 0.82 for creatinine and 0.64 for the UIC: creatinine ratio.

Iodine-specific ISE-based potentiometric methods can be successfully applied as an alternative to existing methods in patients with thyroid diseases. The promising characteristics of the method need to be confirmed in future larger prospective studies.

Correlation between iodine intake and thyroid disorders: a cross-sectional study from the South of China

Great changes have taken place in the incidence of thyroid diseases since the implementation of universal salt iodization (USI). However, the high incidence of thyroid diseases caused by the high iodine intake has been contentious. The aim of this study was to investigate the relationship between iodine intake and thyroid diseases through the comparison of urine iodine concentration (UIC) between patients with thyroid diseases and healthy volunteers and to assess the status of iodine intake among the residents. From November 2013 to May 2014, 905 patients who underwent thyroid surgeries and 272 subjects of healthy controls were enrolled and were divided into two groups: the case group and the control group, respectively. Levels of thyroid hormones and thyroid autoantibodies in serum from blood were analyzed among all the patients. UIC and thyroid B ultrasounds were performed on each participant. The median urinary iodine (MUI) concentration was 184.5 and 169.6 μg/L for case group and control group, respectively (P = 0.003). Significant differences of the MUI were found between healthy controls and patients with Hashimoto's thyroiditis (MUI = 221.3 μg/L), nodular goiter (MUI = 193.5 μg/L), multiple nodules (MUI = 185.9 μg/L), nodule diameter ≥1 cm (MUI = 194.4 μg/L), hyperthyroidism (MUI = 258.7 μg/L), thyroid peroxidase antibody (TPOAb) (+), and thyroglobulin antibody (TGAb) (+) (MUI = 196.4 μg/L), and P values were 0.003, 0.000, 0.002, 0.000, 0.000, and 0.001, respectively. The susceptibility of the thyroid diseases among normal people was significantly associated with female sex (odds ratio (OR) = 3.3), older age (OR = 2.1), and high iodine intake (OR = 1.3). In conclusion, high iodine intake was likely to lead to the occurrence of thyroid diseases, such as Hashimoto thyroiditis, nodular goiter, and hyperthyroidism, through a long-term mechanism. USI should continue to be carried out and individual UIC detection was recommended for the disequilibrium of the iodine nutritional status among normal people.