Goitrogenesis during pregnancy and neonatal hypothyroxinaemia in a borderline iodine sufficient area

Neonatal Thyroid-Stimulating Hormone Reference Intervals in Multi-Ethnics Population

(1) Background: This study is designed to establish thyroid-stimulating hormone (TSH) reference intervals tailored to different neonatal age groups and Indonesian local populations. (2) Methods: Dried blood spot neonatal TSH values, from 1 January 2022 to 31 December 2023, were used to establish the neonatal TSH reference intervals partitioned by sex, gestational age, and ethnic group at different neonatal ages. (3) Results: A significant difference in the reference intervals value was observed in sex, gestational ages, and parental ethnicity groups in different neonatal age subgroups (p < 0.05). Male reference intervals were significantly higher than those of females at all neonatal ages. Late and post-term gestational age categories reference intervals were higher than early and full-term. Among the ethnic groups, Madurese had a higher upper limit TSH reference interval. (4) Conclusions: Our neonatal TSH reference intervals were needed to provide a reference adapted to the local population of Indonesia.

Do Postpartum Maternal Iodine Status or Supplementation Affect Thyroid Function After Delivery? A Systematic Review and Meta-Analysis

The aim of this systematic review and meta-analysis was, for the first time, to explore whether postpartum maternal iodine status or supplementation is associated with thyroid function after delivery. The MEDLINE/PubMed, Web of Science, Embase, and Scopus were searched up to December 2021 to identify relevant studies. The pooled mean thyroid stimulating hormone (TSH), free thyroxine (fT4), and thyroxine (T4) concentrations and 95% confidence intervals (CIs) were estimated based on maternal urinary iodine concentration (UIC) (< 50, 50-100, 100-200, and > 200 µg/L) or breast milk iodine concentration (BMIC) (< 100 µg/L vs. ≥ 100 µg/L) during postpartum. A fixed/random effects model was used based on the absence/presence of heterogeneity, respectively. The study is registered with PROSPERO, number CRD42022336145. A total of 2175 studies were identified, of which 18 were eligible for the meta-analysis. The pooled values for TSH, fT4, and T4 concentrations in all subgroups were within the normal range; however, except for TSH, comparing the 95% CI showed no statistically significant difference among different subgroups. The pooled mean for TSH concentration in women with UIC > 200 µg/L was 2.23 mIU/L, whereas the corresponding values in women with UIC < 50, 50-100 and 100-200 µg/L were 0.56, 0.56 and 0.95 mIU/L, respectively. Thyroid hormones in women with BMIC < 100 µg/L and ≥ 100 µg/L were within the normal range. Iodine supplementation during postpartum was not associated with any differences in thyroid parameters, compared to non-supplemented women. In conclusion, iodine status or supplementation had no effect on thyroid hormones in postpartum women.

Thyroid Volume in Pregnancy is Associated with Parity, Gestational Age, and Body Mass Index in an Iodine-sufficient Area

OBJECTIVE

 We compared thyroid volume (TV) and presence of nodular goiter (NG) in pregnant vs. non-pregnant women in an iodine-sufficient area. We also evaluated the relationship between gestational age, parity, and TV in the pregnant women group, and determined the 2.5th and 97.5th percentiles of normal TV in pregnancy.

METHODS

 This cross-sectional study included 299 healthy women (216 pregnant) without previous thyroid diseases. Thyroid ultrasounds were performed and compared between pregnant and non-pregnant women. The range of normal distribution of TV (2.5th and 97.5th percentiles) in pregnancy was determined after excluding individuals with positive thyroid antibodies, NG, and/or abnormal serum thyrotropin (TSH) or free thyroxine (FT4).

RESULTS

 Thyroid volume was larger among pregnant compared to non-pregnant women (8.6 vs 6.1 cm3; p < 0.001) and was positively correlated with gestational age (rs = 0.221; p = 0.001), body mass index (BMI, rs 0.165; p = 0.002), and FT4 levels (rs 0.118 p = 0.021). Nodular goiter frequency did not differ between the two groups. There was a negative correlation between TV and TSH (rs -0.13; p = 0.014). Thyroid volume was lower among primiparous compared to multiparous patients (7.8 vs 8.9; p < 0.001) and was positively correlated with parity (rs 0.161; p = 0.016). The 2.5th and 97.5th percentiles of TV were 4.23 and 16.47 cm3, respectively.

CONCLUSION

 Thyroid volume was higher in pregnant compared to non-pregnant women and was positively related to parity, BMI, and gestational age in a normal iodine status population. Pregnancy did not interfere with the development of NG.

Exploration of the optimal range of urinary iodine concentration in Chinese pregnant women in mildly iodine-deficient and -sufficient areas

PURPOSE

There is some uncertainty about the optimal ranges for urinary iodine concentration (UIC) during pregnancy. This study aimed to explore associations between maternal UIC and thyroid function in iodine sufficient and mildly iodine deficient areas.

METHODS

It was a cross-sectional study in which 1461 healthy pregnant women were enrolled to collect their blood and urine samples during their routine antenatal care in Tianjin and Wuqiang, China. Wuqiang was a mildly iodine-deficient region, while Tianjin was iodine sufficient. UIC, free triiodothyronine (FT3), free thyroid hormone (FT4), thyroid stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), serum iodine concentration (SIC) including total serum iodine concentration (tSIC) and non-protein bound serum iodine concentration (nbSIC) were assessed during the routine antenatal care visits.

RESULTS

The median UIC in pregnant women was 174 (113, 249) μg/L in Tianjin and 111 (63, 167) μg/L in Wuqiang, respectively. Compared with Tianjin, UIC, FT3 and TSH were lower, and FT4, tSIC, nbSIC, rates of TPOAb and TgAb positivity and the thyroid dysfunction rate (TDR) were higher in Wuqiang (P < 0.001). FT3, FT4, tSIC and nbSIC increased during pregnancy in Tianjin with increasing UIC, while only FT3 and nbSIC increased in Wuqiang (P < 0.05). In Tianjin, the TDR increased with UIC and peaked at UIC ≥ 500 μg/L (P = 0.002), while in Wuqiang, the TDR showed a weak "U-shaped" relationship with UIC and the rate was lowest with UIC 100-149 μg/L.

CONCLUSIONS

In iodine-deficient areas, there was a lower TDR in pregnant women with UIC 100-149 μg/L. We suspected that the optimal UIC criteria recommended by WHO may be a little high for pregnant women in mild-to-moderate iodine-deficient countries.

Optimizing Cord Blood Thyroid Stimulating Hormone Cutoff for Screening of Congenital Hypothyroidism-Experience from Screening 164,000 Newborns in a Tertiary Hospital in India

BACKGROUND AND OBJECTIVES

In our institution, we have an ongoing newborn thyroid screening (NBS) program since July 2001. In the initial 9 months, we used cord blood thyroid-stimulating hormone (TSH) (CBTSH) cutoff of 20 mIU/L and thereafter the cutoff was increased to 25 mIU/L. Our objective was to evaluate whether a CBTSH cutoff of 25 mIU/L is sensitive and cost-effective in NBS of congenital hypothyroidism (CH).

MATERIALS AND METHODS

All in-born babies are screened and those with CBTSH ≥25 mIU/L are recalled for confirmatory TSH/T4/FT4 tests. CH is confirmed with elevated TSH and low T4/FT4. Those with CBTSH 20-24.99 mIU/L were recalled for confirmatory tests in initial period of our NBS and prospectively between January and August 2017. Statistical analysis was done to derive positive predictive value and sensitivity to diagnose CH for each CBTSH between 20 and 30 mIU/L.

RESULTS

A total of 164,163 neonates were screened from July 2001 to August 2017. Of the 2352 babies with CBTSH ≥25-30 mIU/L, 1763 returned for retesting and 5 confirmed as CH (4 gland-in-situ and 1 absent uptake on nuclear scan). Of the 14,742 screened during the study period, 195 of the 293 babies with CBTSH 20-24.99 mIU/L returned for retesting and none diagnosed as CH. A CBTSH of 25 mIU/L has 99.2% sensitivity and 97.5% specificity. A lower screen TSH cutoff 20 mIU/L would result in recall of additional 300 babies/year with no definite improvement in sensitivity.

CONCLUSIONS

Our data justify the continuation of using screen TSH cutoff of 25 mIU/L while using cord blood for NBS in our population. With a diverse and large population, it is important that we use feasible regional screen cutoffs for optimal use of our resources.

Determinants of placental iodine concentrations in a mild-to-moderate iodine-deficient population: an ENVIRONAGE cohort study

Background

Iodine is an essential trace element for the production of thyroid hormones, and plays a key role during the gestational period for optimal foetal growth and (neuro-)development. To this day, iodine deficiency remains a global burden. Previous studies indicate that the placenta can store iodine in a concentration-dependent manner and serve as a long-term storage supply, but studies on the determinants of long-term placental iodine load are limited.

Methods

The placental iodine concentrations were determined for 462 mother-neonate pairs from the ENVIRONAGE birth cohort (Limburg, Belgium). Sociodemographic and clinical variables were obtained from questionnaires and medical files. Determinants of placental iodine concentration were identified using stepwise multiple regression procedures (p value < 0.15). The biological significance of our findings was investigated by measuring the plasma thyroid hormones in maternal and cord blood of 378 participants.

Results

A higher pre-pregnancy BMI, higher gestational weight gain, and alcohol consumption during pregnancy were linked with lower placental iodine storage. Multi-vitamin supplementation during pregnancy and longer gestation were associated with higher levels of placental iodine. Children born during the winter period had on average higher placental iodine levels. Besides, we found a significant positive time trend for placental iodine load over the study period 2013 to 2017. Lastly, we observed positive associations of both the maternal and cord plasma thyroxine concentrations with placental iodine load, emphasizing their biological link.

Conclusions

This study identified some determinants likely presenting a risk of reduced iodine storage during the gestational period of life. Future studies should elucidate the effects of lower placental iodine load on neonatal health, and health later in life.

Thyroglobulin Concentration and Maternal Iodine Status During Pregnancy: A Systematic Review and Meta-Analysis

Background: Literature to date has been inconclusive regarding the value of thyroglobulin (Tg) as a marker of iodine status in pregnant women. This systematic review and meta-analysis is one of the first to assess whether Tg concentration accurately reflects iodine status among pregnant women. Methods: We searched MEDLINE, the Web of Science, the Cochrane Library, Scopus, and other relevant databases to identify relevant studies published in the English language, between January 1988 and December 2018. The criteria for study inclusion in the systematic review were human studies, healthy pregnant women as participants, and available data for maternal urinary iodine concentration (UIC) and Tg level. Each study was assessed for quality and risk of bias. The pooled mean Tg values, and 95% confidence intervals were estimated in a population of women with UIC <150 and UIC ≥150 μg/L during pregnancy. Potential linear or nonlinear dose-response associations between maternal UIC and Tg concentration were examined. Results: Of 814 identified studies, 25 were eligible for inclusion in the meta-analysis. Studies included were conducted in Africa, Asia, Europe, South America, and the Oceania. The pooled mean (95% confidence interval [CI]) Tg concentration in iodine-deficient pregnant women was higher than that in iodine-sufficient pregnant women (10.73 μg/L [5.65-15.82] vs. 7.34 μg/L [2.20-12.47]); a comparison of the 95% CI showed that none of these values was significantly different. No significant differences were observed in Tg concentration between the two groups in each trimester of pregnancy. Dose-response meta-analyses revealed a significant nonlinear association between maternal UIC and Tg concentration during pregnancy. Among populations of pregnant women, an inverse association was found between UIC values <100 μg/L and Tg concentration (p-linearity = 0.007; p-nonlinearity = 0.027); however, higher values of UIC were not associated with Tg concentration. Conclusions: Our meta-analysis showed that Tg concentration can be a sensitive indicator of iodine deficiency, specifically in populations of pregnant women with median UIC <100 μg/L. Further studies are warranted to determine the sensitivity of Tg at different degrees of iodine deficiency during pregnancy.

Iodine Nutrition and Thyroid Function in Pregnant Women Exposed to Different Iodine Sources

Pregnant women are more vulnerable to iodine deficiency and iodine excess. The study aimed to assess the changes in iodine nutrition and thyroid function of pregnant women exposed to different iodine sources resulting in various iodine intakes during pregnancy. From 2016 to 2017, 2004 healthy pregnant women aged 20-35 years from Shandong and Tianjin, China, were enrolled. Urinary iodine concentration (UIC), drinking water iodine content (WIC), thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroid hormone (FT4), thyroglobulin (Tg), serum thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb) were measured. Pregnant women in both Shandong and Tianjin were iodine sufficient, but the median UIC in pregnant women was significantly higher in Shandong (244 μg/L) than that in Tianjin (159 μg/L). No differences were found in UIC over the course of gestation in Shandong. In Tianjin, the UIC decreased during 13-24 weeks and stabilized thereafter. Compared with Tianjin, TSH levels were higher and FT3 and FT4 levels were lower in Shandong. Both FT3 and FT4 significantly decreased during pregnancy in Shandong and Tianjin. TSH and Tg increased over the course of gestation in both Shandong and Tianjin. The iodine status of pregnant women in Tianjin and Shandong were sufficient, but different changing patterns in UIC and thyroid function during pregnancy were presented. More attention should be focused on iodine nutrition of pregnant women, even in iodine-sufficient areas.

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.

Defining the Newborn Blood Spot Screening Reference Interval for TSH: Impact of Ethnicity

CONTEXT

There is variability in the congenital hypothyroidism (CH) newborn screening TSH cutoff across the United Kingdom.

OBJECTIVE

To determine the influences of year, gender, and ethnicity on screening variability and examine whether there is an optimal operational TSH cutoff.

DESIGN AND SETTING

Single center, retrospective population study using blood spot TSH cards received by the Great Ormond Street Hospital Screening Laboratory between 2006 and 2012.

PATIENTS

A total of 824 588 newborn screening blood spot TSH cards.

INTERVENTION

Blood spot TSH results were recorded with demographic data including the Ethnic Category Code.

MAIN OUTCOME MEASURES

The proportions of samples exceeding different TSH cutoffs, ranked by ethnicity.

RESULTS

The proportion of samples exceeding the TSH cutoff increased over time, with the cutoff at 4 mU/L, but not at 6 mU/L. There was a consistent trend with ethnicity, irrespective of cutoff, with the odds ratio of exceeding the TSH cutoff lowest (∼1.0) in White babies, higher in Pakistani and Bangladeshi (>2.0), and highest in Chinese (>3.5).

CONCLUSIONS

The blood spot TSH screening data demonstrate a clear ranking according to ethnicity for differences in mean TSH. This suggests that there may be ethnic differences in thyroid physiology. Ethnic diversity within populations needs to be considered when establishing and interpreting screening TSH cutoffs.

Iodine Status of Vulnerable Populations in Henan Province of China 2013-2014 After the Implementation of the New Iodized Salt Standard

The standard of salt iodine content in China has been adjusted several times since implementation of the universal salt iodization (USI) in 1995. The new standard of iodized salt content was adjusted from 35 ± 15 to 30 ± 9 mg/kg in Henan province in 2012. We aimed to determine whether the vulnerable populations were iodine sufficient after the adjustment of salt iodine content and to provide a guideline for the adjustment of USI policy in China. Two cross-sectional surveys of iodine status in vulnerable populations, including reproductive-age, pregnant and lactating women, infants <2 years, and children aged 8-10 years, were conducted in Henan province in 2013 and 2014. In 2013, the median urinary iodine concentration (mUIC) of reproductive-age women was 200.1 μg/L and that of school children aged 8-10 years was 221.0 μg/L. These mUICs were considered as "more than adequate." The mUICs of reproductive-age women and school children in 2014 showed a significant decline compared to the mUICs in 2013 (P = 0.012 and P = 0.001, respectively). The mUICs of the pregnant women were 204.2 μg/L in 2013 and 202.5 μg/L in 2014, which both met the requirement level recommended by WHO. In 2013, the mUIC of lactating women was 169.1 μg/L and that of infants <2 years was 203.2 μg/L, which were significantly lower than that of 2014 (P < 0.001 and P < 0.001, respectively). The lactating women and infants in 2013 and 2014 were both regarded as "iodine adequate." Iodine status of the vulnerable populations is still adequate as a whole in Henan province after decreasing the salt iodine content. However, the mUIC of school children aged 8-10 years is slightly above the adequate level. To reduce the risk of iodine excess in the general population and prevent the possibility of iodine deficiency of the vulnerable population, it is necessary to explore the appropriate level of iodized salt content.

Inadequate iodine nutrition of pregnant women in an area of iodine sufficiency

PURPOSE

I. R. Iran has been considered iodine replete since 2000, but iodine nutrition of vulnerable subjects is not clear. The main goal of this study was assessment of iodine nutrition and thyroid function in pregnant Iranian women.

METHODS

A total of 1072 pregnant women from ten provinces in the different parts of the country were recruited from November to March 2014. Median urinary iodine concentration (UIC) as the measure of iodine status and serum free T4 (FT4), thyrotropin (TSH), thyroglobulin (Tg), anti-thyroglobulin and anti-thyroid peroxidase antibodies (TgAb and TPOAb) were measured.

RESULTS

Mean ± SD age of the cohort was 27.0 ± 7.2 years and gestational age was 20.7 ± 10.0 weeks. The median UIC for pregnant women was 87.3 μg/L, being 92.1, 86.0 and 76.8 μg/L, in three trimesters of pregnancy, respectively. Median UIC of <100, 100-149, 150-249, 250-499 and ≥500 μg/L was found in 58.4, 19.8, 16.2, 5.13 and 0.46 % of subjects, respectively. Median (IQR) values in the first, second, and third trimesters were 1.7 (0.9-2.8), 2.1 (1.5-2.9), and 2.1 (1.4-2.8) mIU/L for TSH, and 16.4 (12.21-21.13), 14.34 (12.16-19.69), and 14/07 (12.02-18.64) pmol/L for FT4, respectively. The frequency of elevated serum TSH was 9.0 % (6.6 % subclinical, 2.4 % overt hypothyroidism). The frequency of low serum TSH was 0.6 %. The frequency of positive TPOAb was 7.6 %.

CONCLUSIONS

Results of this study have clarified that despite iodine sufficiency of school children in Iran, pregnant women have moderate iodine deficiency and need iodine supplementation.

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.

Maternal iodine status and the thyroid function of pregnant mothers and their neonates in Jaffna District of Sri Lanka

INTRODUCTION

Iodine status of pregnant women and their newborns have not been studied in Jaffna District, Sri Lanka. This study was planned to assess the maternal iodine status and thyroid function at the third trimester of gestation and the thyrotrophin level of their neonate.

METHODS

Four hundred and seventy-seven pregnant women and their newborns were randomly selected among six Medical Officers of Health Divisions out of 12 in Jaffna District, Sri Lanka. Maternal thyroid stimulating hormone (TSH), free thyroxine (fT4), thyroglobulin (Tg), urinary iodine levels, and the neonatal thyrotrophin (nTSH) level were assessed.

RESULTS

In this study, mean age, weight, height, and gestational age of the mothers were 28.95 (±5.46) years, 63.02 (±11.56) kg, 154.39 (±6.00) cm, and 39.33 (±1.37) weeks, respectively. Maternal median urinary iodine concentration (UIC) was 140.0 μg/L (inter-quartile range 126.0-268.0 μg/L). Median values of the maternal serum TSH, fT4, and Tg were 1.9 mIU/L, 12.6 pmol/L, and 21.4 IU/L, respectively. Among the 477 newborns, 50.5% (n = 239) were males. Mean birth weight of newborn was 3.03 (±0.43) kg, while the mean length was 51.1 (±2.1) cm. Among the newborns, 18% (n = 86) had nTSH level > mIU/L and 37.7% (n = 180) within TSH level > mIU/L. nTSH level had positive but very weak correlations with maternal thyroid parameters, that is, UIC (r = 0.06, P = 0.13), fT4 (r = 0.01, P = 0.05), TSH (r = 0.09, P = 0.05), and Tg (r = 0.12, P = 0.03).

CONCLUSION

On the basis of the World Health Organization criteria, the iodine status of pregnant women was inadequate in this region and also nTSH levels indicate moderate iodine deficiency during pregnancy. Therefore, the continuous education on adequate iodine intake during pregnancy and monitoring of iodine status are useful.

Iodine nutrition status in lactating mothers residing in countries with mandatory and voluntary iodine fortification programs: an updated systematic review

BACKGROUND

The aim of this review is to assess data available on iodine nutrition status in lactating mothers residing in countries with mandatory and voluntary iodine fortification programs and/or iodine supplementation.

SUMMARY

A systematic review was conducted by searching articles published between 1964 and 2013 in Pub Med, ISI Web, and Cochrane Library using iodine nutrition, lactation, iodine supplementation, and iodine fortification as keywords for titles and/or abstracts. Relevant articles were included if they reported urinary iodine concentration (UIC) in lactating mothers and, if determined, the type of iodine fortification program and/or iodine supplementation. Forty-two studies met the inclusion criteria. Among these, 21 studies assessed lactating mothers in countries with a mandatory iodine fortification program, 17 studies were from countries with voluntary and/or without iodine fortification programs, and four studies assessed iodine nutrition status in lactating mothers undergoing iodine supplementation. Among countries with mandatory iodine fortification programs, the range of salt iodization level in lactating mothers with a UIC <100 μg/L was between 8 and 40 ppm, whereas among lactating mothers with UIC >100 μg/L, it was between 15 and 60 ppm. Levels of UIC <100 μg/L were observed among lactating women in India, Denmark, Mali, New Zealand, Australia, Slovakia, Sudan, and Turkey, whereas in countries such as Chile, Iran, Mongolia, New Guinea, and Nigeria, the median or mean of UIC was >100 μg/L. There was a median or mean UIC <100 μg/L in nearly all lactating mothers residing in countries where implementation of universal salt iodization program was voluntary, including Switzerland, Australia, New Zealand, Ireland, and Germany. However, in some countries with voluntary iodine fortification programs, such as the United States, Spain, and Japan, a mean or median UIC of >100 μg/L has been reported.

CONCLUSIONS

Although universal salt iodization is still the most feasible and cost-effective approach for iodine deficiency control in pregnant and lactating mothers, UIC in lactating mothers of most countries with voluntary programs and in areas with mandatory iodine fortification is still within the iodine deficiency range, indicating that iodine supplementation in daily prenatal vitamin/mineral supplements in lactating mothers is warranted. However, further investigations are still recommended in this regard.

A Longitudinal Study of Changes in Thyroid Related Hormones among Pregnant Women Residing in an Iodine Deficient Urban Area

Problem Statement. Thyroid gland in women undergoes functional changes during pregnancy. A few studies have described such changes in pregnant women residing in iodine deficient areas. Objective. To document these changes in pregnant women residing in Lahore, a low iodine intake urban area of Pakistan. Patients and Methods. In 254 pregnant women, data of FT₄, FT₃, and TSH during the first and subsequent trimesters were obtained and compared with those of 110 nonpregnant women. These hormones were determined in serum by radioimmunoassay (RIA) techniques using commercial kits. Results. Compared to nonpregnant women mean FT₄ level was decreased, and FT₃ and TSH increased significantly (P < 0.05) in pregnant women. A negative correlation of FT₄ with TSH was observed in all three trimesters. Serum FT₃ was positively correlated with TSH only during the third trimester. As a function of gestation time, FT₄ levels progressively decreased, and FT₃ and TSH levels increased significantly (one-way ANOVA F = 108.2, 17.3, and 44.8, resp.; all P < 0.05) exhibiting thyroid gland adaptations. Conclusion. Pregnancy is associated with significant alterations in thyroid function due to low iodine intake in women residing in study area. The compensated thyroid function poses a risk of thyroid failure in a number of pregnant women.

Assessment of iodine nutrition in pregnant north Indian subjects in three trimesters

OBJECTIVE

The cross-sectional study was carried out to assess the iodine status of pregnant women, using median urinary iodine concentration (MUI) as the measure of outcome, to document the impact of advancing gestation on the MUI in normal pregnancy.

MATERIALS AND METHODS

The present study assessed the MUI in casual urine samples from 50 pregnant subjects of each trimester and 50 age-matched non-pregnant controls.

RESULTS

The median (range) of urinary iodine concentration (UIC) in pregnant women was 304 (102-859) μg/L and only 2% of the subjects had prevalence of values under 150 μg/L (iodine insufficiency). With regard to the study cohort, median (range) UIC in the first, second, and third trimesters was 285 (102-457), 318 (102-805), and 304 (172-859) μg/L, respectively. Differences between the first, second, and third trimesters were not statistically significant. The MUI in the controls (305 μg/L) was not statistically different from the study cohort.

CONCLUSION

The pregnant women had no iodine deficiency, rather had high median urinary iodine concentrations indicating more than adequate iodine intake. Larger community-based studies are required in iodine-sufficient populations, to establish gestation-appropriate reference ranges for UIC in pregnancy.

Gestational changes of thyroid function and urinary iodine in thyroid antibody-negative Japanese women

Iodine is an essential nutrient for thyroid hormone synthesis, and iodine deficiency especially in pregnant and lactating women results in serious damage to their infants. To characterize iodine nutrition throughout gestation by using a food frequency questionnaire (FFQ) and urinary iodine concentration (UIC) measurement, and to establish appropriate gestational age-specific reference ranges for serum TSH and FT₄ in thyroid autoantibody (ThAb) negative euthyroid Japanese women, a total number of 563 pregnant women including 422 subjects with negative ThAbs, 105 postpartum women and their 297 newborn infants were included in the study. Dietary iodine intake (DII) was evaluated by FFQ. Serum TSH, FT₄ and UIC were sequentially determined in the three trimesters of pregnancy and at the 31st postpartum day. The overall median UICs throughout pregnancy and in the postpartum period were 224.0 and 135.0 μg/L, respectively, suggesting sufficient iodine nutrition. The median DII was 842.4 μg/day in pregnant women. The median UIC in the first trimester (215.9 μg/L) significantly decreased in the second trimester (136.0 μg/L). The prevalence of pregnant women with a UIC below 150 μg/L was 31.6% and that in lactating women with a UIC below 100 μg/L was 33.3%. The pattern of gestational change in serum TSH and FT₄ was comparable to that in iodine-sufficient areas. A substantial percentage of women might be at risk for iodine deficiency if there is a restriction of iodine-rich foods. However, iodine supplementation for pregnant women must be carefully balanced against the risk of iodine excess particularly in Japan. Further research in larger samples is needed.

Nutritional Iodine Status in Gestation and its Relation to Geographic Features in Urmia County of Northwest Iran

Background

Iodine is an important component for the proper function of the thyroid and fetal development.

Objective

To evaluate the influence of geographic variation on nutritional iodine status during pregnancy.

Methods

Four hundred eighty-nine women in the first trimester of pregnancy were enrolled. Of these, 419 (85.5%) were from the plain districts and 70 (14.5%) from mountainous regions. Data were obtained on demographic characteristics and accessibility of iodized salt, and samples of table salt were collected. In the third trimester, 322 women remained in the study: 281 (87.2%) from the plains and 41 (12.8%) from the mountainous regions. Salt and urine samples were analyzed for iodine content.

Results

All participants stated that they used iodized table salt. The proportion of salt samples with optimal iodine content (30 ppm) from the plains and mountain regions were 68.7% and 88%, respectively. The median urinary iodine content (UIC) in the plains area in the first and third trimesters was 82 and 119 μg/L, respectively. The corresponding values in the mountain region were 34.5 μg/L and 76 μg/L. The prevalence of subjects with an inadequate iodine intake (UIC < 150 μg/L) in first and third trimester in the plains and mountain regions were 84.5% and 66.9% vs 98.6% and 90.2%, respectively.

Conclusions

The prevalence of pregnant women exhibiting UIC < 150 μg/L in the mountain region was substantially higher than those in the plain district. Our findings also show that the current strategy for eradication of iodine deficiency in school-aged children would not fulfill iodine requirements in pregnancy and that additional source(s) of iodine are required to prevent the adverse effects of iodine deficiency in pregnancy. Further studies are needed to address the cause(s) for the rapid depletion of iodine stores in pregnancy.

Is placental iodine content related to dietary iodine intake?

OBJECTIVE

Delivery of iodine to the foetus depends not only on maternal dietary iodine intake but also on the presence of a functioning placental transport system. A role for the placenta as an iodine storage organ has been suggested, and this study compares the iodine content of placentas from women giving birth at term in Ireland and Iran, areas with median urinary iodine of 79 and 206 μg/l respectively.

DESIGN

Placental cotyledon iodine was measured using an alkaline ashing technique with Sandell-Kolthoff kinetic colorimetry. Samples were taken from six sites from the centre and periphery of each cotyledon. Placentas (Ireland n = 58; Iran n = 45) were obtained from consecutive euthyroid women delivering at term.

RESULTS

The median placental iodine (μg/g wet weight) was significantly higher in Iranian than in Irish women (187·2 μg/g vs 34·3 μg/g; P < 0·001). The distribution of individual placental iodine values showed that values >50μg/g were found in 71·0% of Iranian and in only 21·0% of Irish samples. In Irish subjects, the relationship of placental iodine to pregnant population urinary iodine (UI) (ng/g:μg/l) was 1:2 (40:79), while in Iranians this ratio is closer to 1:1 (211:206).

CONCLUSIONS

These findings, by demonstrating an apparent ability of the placenta to store iodine in a concentration-dependent manner, suggest a hitherto undetected role for the placenta. Whether placental iodine has a role in protecting the foetus from inadequacies in maternal dietary iodine intake is as yet unknown.

Iodine status of the U.S. population, National Health and Nutrition Examination Survey, 2005–2006 and 2007–2008

BACKGROUND

This report presents urinary iodine (UI) concentrations for the general U.S. population during 2005-2006 and 2007-2008. These findings are the fourth and fifth assessments of the population since National Health and Nutrition Examination Survey (NHANES) III (1988-1994), when the median UI concentration for the population decreased from NHANES I (1971-1974).

METHODS

During 2005-2006 and 2007-2008, ~ 5000 participants per year were selected to participate in NHANES. The participants were interviewed and examined. UI concentration was measured on a random one third subsample of 2649 participants, aged 6 years and older in 2005-2006, and in all participants in 2007-2008. These urine iodine concentrations are representative of the general U.S. population by age, sex, and race/ethnicity.

RESULTS

(i) The median UI concentrations for the general U.S. population in 2005-2006 and 2007-2008 were 164 mg/L (95% confidence interval [CI] 154-174) and 164 mg/L (95% CI 154-173), respectively. Also, the proportions of the population with a UI concentration of < 50 mg/L during these survey periods were 9.8% ± 1.3% and 8.8% ± 0.4%, respectively. The median UI concentration and prevalence of ≥ 200 mg/L appeared to be higher in children and persons ≥ 70 years than in other age groups. (ii) In both surveys, children aged 6-11 years had median UI concentrations of ≥ 200 mg/L, and about 5% of them had a UI concentration of < 50 mg/L. (iii) All pregnant women (sample size 184) surveyed during 2005-2008 had a median UI concentration of 125 mg/L (95% CI 86-198), and 56.9% ± 7.9% of this group had a UI concentration of < 150 mg/L. UI concentrations were lower among non-Hispanic black survey participants than non-Hispanic white and Mexican-American participants.

CONCLUSIONS

These findings affirm the stabilization of UI concentration and adequate iodine nutrition in the general U.S. population since 2000. However, certain groups likely do not achieve a sufficient dietary iodine intake according to the World Health Organization. The needs of these vulnerable groups and the inadequacy of their dietary iodine intake should be addressed in future efforts.

Trimester- and method-specific reference intervals for thyroid tests in pregnant Chinese women: methodology, euthyroid definition and iodine status can influence the setting of reference intervals

OBJECTIVE

The importance of diagnosis and treatment of thyroid dysfunction during pregnancy has been widely recognized. We therefore established trimester- and method-specific reference intervals for thyroid testing in pregnant women according to the NACB recommended criteria. Several factors can affect the setting of reference intervals, in particular manufacturer's methodology, euthyroid definition and iodine status.

DESIGN

Cross-sectional dataset analysis.

SUBJECTS

Five hundred and five normal pregnant women at different stages of gestation were rigorously selected for setting reference intervals. All were healthy, iodine sufficient, euthyroid and negative for both serum thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb).

MEASUREMENTS

Thyrotrophin (TSH), total and free thyroxine (TT4 and FT4), total and free triiodothyronine (TT3 and FT3) and anti-TPOAb and anti-TgAb were measured using the Bayer ADVIA Centaur system. Iodine content in drinking water, salt and urine was determined by national standard methods. The 2·5th and 97·5th percentiles were calculated as the reference intervals for thyroid hormone levels during each trimester.

RESULTS

All participants had long-term consumption of iodized salt and median urinary iodine of 150-200 μg/l during each three trimester. The reference intervals for the first, second and third trimesters were, respectively, TSH 0·03-4·51, 0·05-4·50 and 0·47-4·54 mIU/l and FT4 11·8-21·0, 10·6-17·6 and 9·2-16·7 pmol/l. The manufacturer's method, euthyroid definition and iodine status may influence TSH and FT4 reference intervals. Alterations in thyroid hormone concentrations during pregnancy differed at different stage of gestation and to those of a nonpregnant state.

CONCLUSIONS

The trimester- and method-based reference intervals for thyroid tests during pregnancy are clinically appropriate. Some variables should be controlled when establishing reference intervals.

Iodine intake in Portuguese pregnant women: results of a countrywide study

BACKGROUND

Iodine is the key element for thyroid hormone synthesis, and its deficiency, even moderate, is harmful in pregnancy, when needs are increased, because of its potential deleterious effects on fetal brain development. In Portugal, no recent data on iodine intake exists. The objective of this countrywide study was to analyze iodine status in pregnant Portuguese women in order to propose adequate measures to the health authorities.

SUBJECTS AND METHODS

Using a fast colorimetric method, urine iodine concentration (UIC) was evaluated in 3631 pregnant women followed in 17 maternity hospitals from hinterland and coastal areas in Continental Portugal and the Portuguese islands of Açores and Madeira.

RESULTS

Median UIC value was 84.9 μg/l (range 67.6-124.1) in Continental Portugal, 69.5 μg/l in Madeira, and 50.0 μg/l in Açores. The percentage of satisfactory values (>150 μg/l) was 16.8, ranging from 8.8 to 34.1 in the Continent, and being 8.2 in Madeira and 2.3 in Açores. The percentage of values below 50 μg/l was 23.7, ranging from 14.0 to 37.4 in the Continent, 33.7 in Madeira, and 50.0 in Açores.

CONCLUSIONS

Our results point to an inadequate iodine intake in pregnant women assisted in most Portuguese maternity hospitals. Considering the potential deleterious effects of inadequate iodine supply in pregnancy, iodine supplementation is strongly recommended in this period of life.

Iodine status and thyroid volume changes during pregnancy: results of a survey in Aran Valley (Catalan Pyrenees)

The Aran Valley (Catalan Pyrenees, Spain) has a long-standing history of iodine deficiency. A survey was performed to determine the prevalence of iodine deficiency (urinary iodine<150 microg/l) in pregnant women from this region during the 1st and 3rd trimesters of gestation and to evaluate the changes in thyroid volume (TV). Of all the registered pregnancies in the area, in the first semester of the year 2000, 35 women (90%) were studied. Urinary iodine (UI) was measured and a thyroid ultrasonography performed during the 1st and 3rd trimester and their iodized salt consumption was recorded. Of the whole group, 77.1% of pregnant women reported regular intake of iodized salt.Median UI in the first trimester was 134.5 microg/l. Iodine deficiency was observed in 57.1%of women in the 1st trimester and in 46.7% in the 3rd trimester (p=0.1). In 10 women supplemented with iodine (150 microg/day) from the 1st trimester, median UI increased from 138.5 microg/l in the 1st trimester to 168 mug/l in the 3rd trimester (p=0.037), and no changes were observed in the rest. TV increased in the whole group during pregnancy (median 7.5 ml in the 1st trimester vs 9.5 ml in the 3rd trimester; p<0.001). The change in TV was significant in those cases with iodine deficiency in the 1st trimester, 3rd trimester or both (median 7.5ml in the 1st trimester vs 10.01 ml in the 3rd trimester; p=0.001) and between multiparous women (8.2 vs 10.9 ml; p=0.005). In 2000, iodine deficiency among pregnant women in the Aran Valley was still very high. Iodine deficiency as well as multiparity contributes to goitrogenesis during pregnancy. Taking this data in account, pre-conceptional supplements with iodine are required for its prevention.

The influence of gestational stage on urinary iodine excretion in pregnancy

INTRODUCTION

Median urinary iodine concentration (UIC) is the most commonly used indicator of population iodine nutrition. However, its validity as an indicator of dietary intake relies on a stable relationship between dietary iodine intake and urinary excretion. Physiological alterations in normal pregnancy, such as increased glomerular filtration rate, potentially invalidate UIC as an assessment tool in pregnancy.

OBJECTIVE

The objective of the study was to document the impact of advancing gestation on UIC in normal pregnancy and determine whether the current reference intervals for general population iodine monitoring are appropriate for use in the context of pregnancy.

DESIGN

Tasmania has a well-described history of mild iodine deficiency (school-age median UIC of 84 microg/liter). We assessed UIC in 759 urine samples from 431 women attending the Antenatal Clinic at the Royal Hobart Hospital, Tasmania's primary teaching hospital.

MAIN OUTCOME

The overall median UIC during pregnancy was 75 microg/liter (95% confidence interval 70.03-79.97 microg/liter) at a median gestation of 19.4 wk. Stratification by gestation, however, revealed a dynamic relationship between ioduria and gestation. Median UIC was elevated in early pregnancy and subsequently declined with advancing gestation.

CONCLUSION

In this mildly iodine-deficient population, current reference intervals for UIC overestimated the adequacy of iodine nutrition during the first and early second trimester of pregnancy. Gestation-specific UIC reference intervals are required to classify iodine nutrition during pregnancy. This is particularly important in populations with borderline iodine deficiency.

Iodine requirements during pregnancy, lactation and the neonatal period and indicators of optimal iodine nutrition

OBJECTIVE

This paper re-evaluates the requirements for iodine during pregnancy, lactation and the neonatal period, and formulates original proposals for the median concentrations of urinary iodine (UI) that indicate optimal iodine nutrition during these three critical periods of life. This paper also discusses the measurements that are used to explore thyroid functions during the same periods.

DESIGN

An extensive and critical review of the literature on thyroid physiopathology during the perinatal period.

SETTING

Human studies conducted in various regions throughout the world.

SUBJECTS

Pregnant women, lactating women, and newborns.

RESULTS

The following proposals are made after extensive review of the literature: the requirement for iodine by the mother during pregnancy is 250-300 microg day-1; during lactation the requirement is 225-350 microg day-1; and during the neonatal period the requirement of the infant is 90 microg day-1. The median UI that indicates an optimal iodine nutrition during these three periods should be in the range of 150-230 microg day-1. These figures are higher than recommended to date by the international agencies.

CONCLUSIONS

Pregnant women and young infants, but especially the second group, are more sensitive to the effects of an iodine deficiency (ID) than the general population because their serum thyroid-stimulating hormone (TSH) and thyroxine are increased and decreased, respectively, for degrees of ID that do not seem to affect thyroid function in the general population. Systematic neonatal thyroid screening using primary TSH could be the most sensitive indicator to monitor the process of ID control.

Gestation-specific thyroxine and thyroid stimulating hormone levels in the United States and worldwide

BACKGROUND

Euthyroid women experience dramatic changes in the demand for thyroid hormone production as early as the first trimester of pregnancy. These changes are important for fetal neurodevelopment and organ development as well as maternal health and succesful full term pregnancy. Therefore, gestation-specific reference intervals assist in appropriate clinical management of thyroid disease in pregnancy to ensure maternal and fetal health.

OBJECTIVE

To determine trimester-specific levels of serum thyroxine (T4) and thyroid stimulating hormone (TSH) in the U.S. population based on the National Health and Nutrition Survey III and compare these with published trimester-specific T4 and TSH means and medians obtained in other countries worldwide.

METHODS

Trimester-specific means and medians for T4 and TSH were determined for the U.S. population based on the National Health and Nutrition Survey III database (1988-1994). These were compared with trimester-specific means and medians of other countries in the published literature.

RESULTS

Mean serum T4 levels for the U.S. population were 141.35, 152.95, and 142.65 nmol/L in the three trimesters, respectively, whereas mean serum TSH levels were 0.91, 1.03, and 1.32 mIU/L.

CONCLUSIONS

Gestation-specific mean T4 and TSH levels for the representative U.S. population are well within the trimester-specific reference intervals. T4 and TSH measured during pregnancy in longitudinal and cross-sectional studies of populations worldwide demonstrate that, in some populations, T4 and TSH levels are outside the normal trimester-specific reference intervals.

The impact of iodised salt or iodine supplements on iodine status during pregnancy, lactation and infancy

Objectives:Monitoring of iodine status during pregnancy, lactation and infancy is difficult as there are no established reference criteria for urinary iodine concentration (UI) for these groups; so it is uncertain whether iodized salt programs meet the needs of these life stages.

Design and Subjects:The method used in this paper was: 1) to estimate the median UI concentration that reflects adequate iodine intake during these life stages; and 2) to use these estimates in a review of the literature to assess whether salt iodisation can control iodine deficiency in pregnant and lactating women, and their infants.

Results:For pregnancy, recommended mean daily iodine intakes of 220-250 μg were estimated to correspond to a median UI concentration of about 150 μg l− 1, and larger surveys from the iodine sufficient countries have reported a median UI in pregnant women ≥ 140 μg l− 1. Iodine supplementation in pregnant women who are mild-to-moderately iodine deficient is beneficial, but there is no clear affect on maternal or newborn thyroid hormone levels. In countries where the iodine intake is sufficient, most mothers have median breast milk iodine concentration (BMIC) greater than the concentration (100-120 μg l− 1) required to meet an infant's needs. The median UI concentration during infancy that indicates optimal iodine nutrition is estimated to be ≥ 100 μg l− 1. In iodine-sufficient countries, the median UI concentration in infants ranges from 90-170 μg l− 1, suggesting adequate iodine intake in infancy.

Conclusions:These findings suggest pregnant and lactating women and their infants in countries with successful sustained iodised salt programs have adequate iodine status.

Iodine status among pregnant women in Kuwait

Up to now, little has been known about iodine intake and the prevalence of iodine deficiency (ID), if any, in Kuwait. Urinary iodine excretion (UIE) and changes in thyroid function during pregnancy were thus evaluated.

METHODS

Urinary iodide level was measured in random urine samples collected from 326 pregnant women at different gestational trimesters. Blood samples were drawn for free T4 (FT4) and TSH level determination.

RESULTS

Median UIE levels fall within the normal range during all gestational trimesters i.e. >100 microg/l. However, if the new suggested recommendation for pregnant women <140 microg/l, is applied, median UIE values during trimesters 2 and 3 indicate ID. Mean serum TSH levels increased between trimesters 1 and 3 (p<0.05), whereas serum FT4 decreased between first and second trimesters (p<0.05), and this reduction continued at the third trimester. Furthermore, an increase in TSH levels for subjects with mild and moderate ID (Mi and Mo, respectively) were noticed (p<0.05) during the second trimester. However, FT4 levels dropped in subjects with Mi and Mo ID during the first trimester (p<0.05). In conclusion, these results suggest that 56.8% of pregnant women had median UIE level <145 microg/l, associated with high TSH and low FT4 levels.

CONCLUSION

Data obtained may indicate insufficient iodine intake among pregnant women in Kuwait.

Iodine nutrition of pregnant and lactating women in Hong Kong, where intake is of borderline sufficiency

Objective: To describe the iodine nutrition of pregnant and lactating women in Hong Kong, where intake is of borderline sufficiency.

Design: Review of cross-sectional and prospective studies.

Setting: China, Hong Kong Special Administrative Region (SAR).

Subjects: Pregnant and lactating women.

Results: Studies of pregnant women in Hong Kong SAR have revealed an increase in the urinary iodine (UI) concentration as pregnancy advances. A significant percentage of women had a sub-normal serum thyroid hormone concentration at full term. Although iodine is concentrated by the mammary gland, 19% of all mothers had low iodine concentrations in their breast milk. The moderate correlation between the concentrations of iodine in breast milk and urine suggests that an adequate maternal urinary iodine concentration cannot reliably indicate that an infant is getting enough iodine in breast milk. Therefore, some breast-fed infants may still be at risk of low iodine intake, and additional iodine supplements, other than salt iodisation, would be warranted in this population.

Conclusions: The currently recommended intake of iodine through universal salt iodisation may not be adequate for pregnant and lactating women, and supplementation during pregnancy and lactation should be further considered in light of the latest recommendations.

Tandem mass spectrometry improves the accuracy of free thyroxine measurements during pregnancy

OBJECTIVE

Pregnancy is a time of rapidly changing demands on the thyroid axis, and knowledge of thyroid hormone levels, especially during the first trimester, is important for ensuring maternal and fetal health. The thyroid hormone assays currently in use become more inaccurate at extremes of binding protein concentrations and when heterophilic antibodies are present. Pregnancy is characterized by both these conditions, making accurate determination of free thyroid hormone levels by conventional direct analog immunoassay methods difficult. The objective of this study was to characterize the performance of a novel tandem mass spectrometric assay for free thyroxine during the physiologic conditions of pregnancy.

DESIGN

Healthy women without a history of thyroid abnormalities were recruited from the obstetrics and gynecology and endocrinology clinics of a university medical center and their thyroid status was monitored. Free thyroxine levels were assessed by both immunoassay and tandem mass spectrometry during the course of their pregnancy. Serum thyrotropin levels were also measured. The distributions of free thyroid concentrations obtained by the two assays were compared.

MAIN OUTCOME

The tandem mass spectrometry and immunoassay values did not correlate well with each other. However, tandem mass spectrometry values correlated well with the current gold standard equilibrium dialysis values. Moreover, the good agreement between equilibrium dialysis and tandem mass spectrometry was maintained across all weeks of gestation.

CONCLUSIONS

We conclude that tandem mass spectrometry has a superior performance to immunoassay for the measurement of free thyroxine during pregnancy. Furthermore, it is ideally suited to generating trimester-specific reference intervals for free thyroxine levels. Future studies will determine if it is a better assay to use in most clinical circumstances.

Thyroid medications during pregnancy

Euthyroid women experience dramatic changes in their thyroid physiology in order to accommodate the presence of placental and fetal tissues. These adaptations to the pregnant state make it crucial to develop reliable trimester-specific intervals for thyroid parameters. Use of non-pregnant reference intervals could lead to erroneous assessment of thyroid status in this rapidly changing hormonal environment. Only with a full appreciation of physiologic changes in thyroid parameters during a euthyroid pregnancy, can thyroid dysfunction be appropriately diagnosed and managed. Iodine sufficiency during pregnancy can be achieved with supplementation using a multivitamin. Both hypothyroidism and hyperthyroidism should be diagnosed using the appropriate reference intervals for pregnancy. Hypothyroid women are best treated with a specific brand of levothyroxine. Hypothyroidism should ideally be treated prior to conception. If newly recognized during pregnancy, it should be fully treated as early as possible. Frequent monitoring of thyroid status is essential as many women demonstrate an increased requirement for thyroid hormone during the first trimester. Although mild hyperthyroidism may be well tolerated during pregnancy, overt hyperthyroidism requires treatment. Thionamides are the mainstay of therapy. Following their initiation, close monitoring is required to avoid maternal and fetal hypothyroidism. There are occasional circumstances when other medical therapy or surgical therapy may be employed for hyperthyroidism. Thyroidectomy is generally safe in the second trimester in an appropriately prepared woman. There is limited data about the role and safety of oral contrast agents, iodine, amiodarone, and perchlorate. Radioiodine therapy is contradicted during pregnancy.

Development of a health-protective drinking water level for perchlorate

We evaluated animal and human toxicity data for perchlorate and identified reduction of thyroidal iodide uptake as the critical end point in the development of a health-protective drinking water level [also known as the public health goal (PHG)] for the chemical. This work was performed under the drinking water program of the Office of Environmental Health Hazard Assessment of the California Environmental Protection Agency. For dose-response characterization, we applied benchmark-dose modeling to human data and determined a point of departure (the 95% lower confidence limit for 5% inhibition of iodide uptake) of 0.0037 mg/kg/day. A PHG of 6 ppb was calculated by using an uncertainty factor of 10, a relative source contribution of 60%, and exposure assumptions specific to pregnant women. The California Department of Health Services will use the PHG, together with other considerations such as economic impact and engineering feasibility, to develop a California maximum contaminant level for perchlorate. We consider the PHG to be adequately protective of sensitive subpopulations, including pregnant women, their fetuses, infants, and people with hypothyroidism.

Iodine intake in pregnancy in Ireland — A cause for concern?

BACKGROUND

Adequate dietary iodine intake is necessary to maintain maternal thyroid function at a level permitting normal neuropsychological development of the foetus.

AIMS AND METHODS

To determine dietary iodine status by measuring urinary iodine excretion (UIE), proportional to dietary intake, in Irish mothers during the first trimester of pregnancy.

RESULTS

Median UIE showed seasonal variations, being lower in summer than in winter. The median values in pregnant women were, summer 45microg/l, winter 68microg/l. Equivalent values for controls were 43 and 91microg/l respectively. UIE required to achieve WHO recommended daily iodine intakes would be 120-180microg/l. In the Irish subjects UIE values suggestive of iodine deficiency (<50microg/l) were observed in 55% of pregnant women tested in summer and 23% in winter. Dairy milk iodine, a major dietary iodine source, showed similar variation.

CONCLUSIONS

While there is as yet no available evidence of widespread thyroid hypofunction in the Irish obstetric population, the findings are a cause of concern, which if confirmed by a more comprehensive investigation, may indicate the need for iodine prophylaxis.

The genetics of euthyroid familial goiter

In endemic goiters, thyroidal enlargement reflects an increase in cell proliferation triggered by low dietary iodine. However, not all individuals in the same iodine-deficient regions develop a goiter, and iodine supplementation does not prevent goiter development in all treated subjects. Familial clustering of goiters, usually with an autosomal-dominant pattern of inheritance, has repeatedly been reported. Moreover, other environmental and etiological factors are likely to be involved in the development of euthyroid goiter. Therefore, a multifactorial etiology based on complex interactions of an individual's genetic makeup and environment is likely. Family and twin studies suggest a considerable influence by a strong genetic component in euthyroid familial goiter.

Long-term environmental exposure to perchlorate through drinking water and thyroid function during pregnancy and the neonatal period

We have conducted a longitudinal epidemiologic study among pregnant women from three cities in northern Chile: Taltal with 114 microg/L, Chañaral with 6 microg/L, and Antofagasta with 0.5 microg/L perchlorate in the public drinking water. We tested the hypothesis that long-term exposure to perchlorate at these levels may cause a situation analogous to iodine deficiency, thus causing increases in thyrotropin (TSH) and thyroglobulin (Tg) levels and decreased levels of free thyroxine (FT4), in either the mother during the early stages of gestation or the neonate at birth, or in the fetus cause growth retardation. We found no increases in Tg or TSH and no decreases in FT4 among either the women during early pregnancy (16.1 +/- 4.1 weeks), late pregnancy (32.4 +/- 3.0 weeks), or the neonates at birth related to perchlorate in drinking water. Neonatal birth weight, length, and head circumference were not different among the three cities and were consistent with current U.S. norms. Therefore, perchlorate in drinking water at 114 microg/L did not cause changes in neonatal thyroid function or fetal growth retardation. Median urinary iodine among the entire cohort was 269 microg/L, intermediate between that of pregnant women in the United States at National Health and Nutrition Examination Survey (NHANES) I and at NHANES III and consistent with current World Health Organization (WHO) recommendations. Median breast milk iodine was not decreased in the cities with detectable perchlorate. Analysis of maternal urinary perchlorate excretion indicates an additional dietary source of perchlorate.

Are detection and treatment of thyroid insufficiency in pregnancy feasible?

A workshop entitled, "The Impact of Maternal Thyroid Diseases on the Developing Fetus: Implications for Diagnosis, Treatment, and Screening," was held in Atlanta, Georgia, January 12-13, 2004. The workshop was sponsored jointly by The National Center on Birth Defects and Developmental Disabilities of The Centers for Disease Control and Prevention (CDC) and The American Thyroid Association. This paper reports on the individual session that examined the ability to detect and treat thyroid dysfunction during pregnancy. For this session, presented papers included: "Laboratory Reference Values in Pregnancy" and "Criteria for Diagnosis and Treatment of Hypothyroidism in Pregnancy." These presentations were formally discussed by invited respondents and by others in attendance. Salient points from this session about which there was agreement include the following: thyrotropin (TSH) can be used as marker for hypothyroidism in pregnancy, except when there is iodine deficiency usually evidenced by elevated serum thyroglobulin (Tg). We need more longitudinal studies of TSH during pregnancy in iodine-sufficient populations without evidence of autoimmune thyroid disease to develop trimester-specific TSH reference ranges. Current free thyroxine (FT4) estimate methods are sensitive to abnormal binding-protein states such as pregnancy. There is no absolute FT4 value that will define hypothyroxinemia across methods. Total thyroxine (TT4) changes in pregnancy are predictable and not method-specific. TT4 below 100 nmol/L (7.8 microg/dL) is a reasonable indicator of hypothyroxinemia in pregnancy. Women with known hypothyroidism and receiving levothyroxine (LT4) before pregnancy should plan to increase their dosage by 30% to 60% early in pregnancy. Women with autoimmune thyroid disease prior to pregnancy are at increased risk for thyroid insufficiency during pregnancy and postpartum thyroiditis and should be monitored with TSH during pregnancy.

Assessment of iodine intake in mildly iodine-deficient pregnant women by a new automated kinetic urinary iodine determination method

Maternal iodine deficiency can compromise the thyroid status of the mother, fetus and newborn child. Therefore, it is important to assess the iodine excretion level of groups of pregnant women. In this study we aimed to determine iodine intake in pregnancy using a recently reported automated kinetic method for urinary iodine determination. Urinary iodine measurements of 123 pregnant women (18 first, 28 second and 77 third trimester) were carried out using a new automated kinetic assay based on the Sandell-Kolthoff reaction at 37°C and its kinetic measurement at 340nm in a random-access automated analyzer after ammonium persulfate digestion at 95°C in a water bath with ±0.1°C precision. Statistical analyses were carried out using SPSS software. Whole group, first trimester, second trimester and third trimester urinary iodine concentrations (mean±SD) in pregnant women were 1.13±0.81, 1.08±0.71, 0.86±0.58 and 1.27±0.87μmol/L, respectively. The urinary iodine concentration significantly increased with gestational age (p<0.05). We found that our study group was mildly iodine-deficient according to WHO criteria. Furthermore, the pregnant women were found to be mildly iodine-deficient in the first and third trimesters and moderately so in the second trimester. The only statistical difference was between second and third trimester values (p<0.05). Even though the increased iodine deficiency in the second trimester is not useful for early detection of iodine deficiency in pregnancy, the severity of this deficiency in the second trimester may lead to important effects on thyroid metabolism for both mother and fetus. Our study suggests that the iodine excretion of pregnant women living in iodine-deficient areas could be assessed using this fast and automated method.

The regulation of thyroid function during normal pregnancy: importance of the iodine nutrition status

The main change in thyroid function associated with the pregnant state is the requirement of an increased production of thyroid hormone that depends directly upon the adequate availability of dietary iodine and integrity of the glandular machinery. Physiologic adaptation takes place when the iodine intake is adequate, while this is replaced by pathologic alterations when there is a deficient iodine intake. Pregnancy acts typically, therefore, as a revelator of underlying iodine restriction. Iodine deficiency (ID) has important repercussions for both the mother and the fetus, leading to sustained glandular stimulation, hypothyroxinemia and goitrogenesis. Furthermore, because severe ID may be associated with an impairment in the psycho-neuro-intellectual outcome in the progeny-because both mother and offspring are exposed to ID during gestation (and the postnatal period), and because ID is still prevalent today in several European countries-it has been proposed already in the early 1990s that iodine supplements be given systematically to pregnant and breast-feeding women. Particular attention is required to ensure that pregnant women receive an adequate iodine supply, by administering multivitamin tablets containing iodine supplements, in order to achieve the ideal recommended dietary allowance of 200-250 microg iodine/day.

Reference intervals for free thyroxine, total triiodothyronine, thyrotropin and thyroglobulin for Quebec newborns, children and teenagers

OBJECTIVE

Paediatric reference values, although essential for interpreting patients' results, are scarce. Moreover, they are often population- and instrument-dependent. We have measured free thyroxine (Free T(4)), total triiodothyronine (Total T(3)), thyroglobulin (Tg) and thyrotropin (TSH) in samples obtained from groups of newborns, children and adolescents.

SUBJECTS AND METHODS

Blood samples collected from healthy children and teenagers (100 girls and 100 boys) of age groups ranging between 9-10, 11-14 and 15-17 years and selected randomly from a cohort representative of the Quebec population, were used. Samples from infants of age ranging between 1 day and 2 years (n = 99) were obtained from a hospital-based population with benign conditions unlikely to affect thyroid function. Variables were measured on the Access 2 immunosystem.

RESULTS

Free T(4), Tg and TSH levels declined significantly with age. However, Total T(3) level presented a nonlinear variation with age, being lower in the first month of life.

Epidemiological survey of thyroid volume and iodine intake in schoolchildren, postpartum women and neonates living in Ulaan Baatar

OBJECTIVE

Although endemic goiter had been recognized in most parts of the country, there are few available data on iodine-deficiency disorders (IDDs) in Mongolia. This study aimed to characterize the current status of iodine deficiency in Ulaan Baatar, Mongolia's capital city.

DESIGN

Cross-sectional, observational study designed and performed according to the surveillance methods for IDD prevalence recommended by WHO/UNICEF/ICCIDD.

SUBJECTS

A total of 505 schoolchildren aged 9-14 years (237 girls and 268 boys) and 138 mothers and their neonatal infants were selected to clinical and biochemical examination of the thyroid in 1996 and 1999.

MEASUREMENTS

The anthropometric measurements, thyroid volume determined by ultrasound, blood TSH and FT4 concentrations, urinary iodine concentration and iodine content of salt consumed in households.

RESULTS

Median thyroid volumes based on age were generally higher than those in iodine-sufficient areas and comparative to those reported in mild iodine-deficiency areas. Application of the updated WHO/ICCIDD reference values in iodine-replete European schoolchildren to the Mongolian children aged 10-12 years resulted in a goiter prevalence of 43.3%. The median value of urinary iodine concentration was 152.5 micro g/l (1.20 micro mol/l) and 40.3% of children excreted iodine below 100 micro g/l. Iodized salt (> 40 ppm) was consumed in 63.1% of households and in the children using noniodized salt their urinary iodine concentration was lower than those using ionized salt. In postpartum women, median thyroid volume and urinary iodine concentration were 11.3 ml and 107 micro g/l (0.84 micro mol/l), respectively, and 46% of women excreted less than 100 micro g/l (0.79 micro mol/l) of iodine. Of their neonates, 17.8% had elevated blood TSH levels (> 5 mU/l). In a 1999 survey, the goiter prevalence and ratio of low iodine excretion in schoolchildren decreased to 29.8% and 31.3%, respectively, while median urinary iodine concentration remain unchanged (160 micro g/l; 1.26 micro mol/l).

CONCLUSION

The present study clearly indicates the presence of mild iodine deficiency in Mongolia. Enlarged thyroid gland and normal iodine excretion observed in schoolchildren living in Ulaan Baatar may result from the residual effects of iodine deficiency previously and presumably still exist in the city. Slight reduction in the rate of children with enlarged thyroid and low urinary iodine excretion after the onset of national iodinization programme suggests incomplete normalization of thyroid volume in children and that the correction of iodine deficiency is now in progress in Ulaan Baatar. Further nationwide surveys together with monitoring the progress of the national programme eliminating IDD are required in suburban areas surrounding the city and also in rural areas.

Cricoid pressure: beware the patient with a goitre

A case of acute thyroid swelling is reported following intubation of a young woman with a pre-existing small goitre. The thyroid enlargement then distorted the airway, necessitating an emergency thyroidectomy. The application of cricoid pressure was believed to have caused the intrathyroidal bleeding and the complications of cricoid pressure are reviewed.

Urinary iodine percentile ranges in the United States

BACKGROUND

The status of iodine nutrition of a population can be determined by measurement of urinary iodine concentrations since it is thought to indicate dietary iodine intake. Normally, these results are compared to population-based criteria, since there are no reference ranges for urinary iodine.

OBJECTIVE

To determine the percentile ranges for urinary iodide (UI) concentrations in normal individuals in the United States.

MATERIALS AND METHODS

The third National Health and Nutrition Examination Survey (NHANES III) (1988-1994) database of the civilian, non-institutionalized, iodine-sufficient US population was used. The 2.5th to 97.5th percentile ranges for urinary iodine and for urinary iodine per gram creatinine ratio (UI/Cr) (microg/g) were calculated for females and males, 6-89 years of age, each stratified by age groups.

RESULTS AND CONCLUSIONS

We calculated the percentile ranges for urinary iodine. After exclusions of subjects with goiter or thyroid disease, the study sample included 21,530 subjects; 10,439 males and 11,091 females. For women of childbearing age (14-44 years), urinary iodine concentration 2.5th to 97.5th percentiles are 1.8-65 microg/dl or 36-539 microg/g creatinine. For pregnant women, the ranges are 4.2-55 microg/dl or 33-535 microg/g creatinine.

Controversies in urinary iodine determinations

Iodine deficiency (ID) is associated with increased prevalence of goiter, increased risk for neurodevelopmental disorders, and is the world's leading cause of intellectual deficits. Iodine nutritional status of a population is assessed by measurements of urinary iodine concentrations which are also used to define, indicate, survey and monitor iodine deficiency and consequently its treatment. Several methods are available for urinary iodine determination. Discussed here are some of the limitations and controversies related to urinary iodine determinations, and recent findings with emphasis on measurements of urinary iodine concentrations in children and during pregnancy.