Serum insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 levels in severe iodine deficiency

Iodine deficiency is an important public health problem worldwide. It is well known that it has severe consequences such as brain damage, developmental delay, deficits in hearing and learning and lower intellectual attainment. It also has a negative impact on growth. In this study, we aimed to address this issue and we assessed height standard deviation scores of children living in an area of severe iodine deficiency in comparison to those living in a mild iodine deficiency area. Serum levels of insulin-like growth factor-I (IGF-I), IGF-binding protein-3 (IGFBP-3), thyroxine (T4), and thyroid stimulating hormone (TSH) were also analyzed to investigate the mechanisms by which iodine depletion leads to growth failure. Pubertal children in a severe iodine deficient SID area had lower height standard deviation scores (HSDS), IGF-I and IGFBP-3 levels than those living in mild iodine deficient MID area. Similar findings could not be elucidated in the prepubertal age group. The major determinants of HSDS were age, IGF-I, IGFBP-3 and TSH. IGF-I and IGFBP-3 were negatively correlated with T4. These findings suggest that iodine deficiency has a negative impact on growth, as well as IGF-I and IGFBP-3 levels. This effect seems to be due to the derangements in thyroid hormone economy arising from iodine depletion. The degree of this impact may be related to the duration of iodine depletion or may be dependent on the developmental stage of the organism at the time of iodine depletion.     

Iodine deficiency during infancy and early childhood in Belgium: does it pose a risk to brain development?

Iodine deficiency is well documented in Belgium in adults including pregnant women, adolescents, schoolchildren, and neonates, but no data are available in the age group 6 months–3 years. We investigated the status of iodine nutrition in 111 healthy subjects in this age group in an attempt to evaluate the risk of brain damage due to iodine deficiency in Belgium. In 244 casual urine samples collected in these subjects, the median concentration of iodine was 101 μg/l vs 180–220 μg/l under normal conditions. The daily supplementation of the subjects with a physiological dose of 90 μg iodine was followed by a slow and progressive increase of urinary iodine, which reached a normal level only after a delay of about 30 weeks of therapy. This observation suggests that part of the supplement of iodine offered to the children was stored in their thyroid glands until the iodine content of the gland had reverted to normal, reflecting the state of hyperavidity of the thyroid for iodide characteristic of iodine deficiency. In conclusion, infants and young children in Belgium are as iodine deficient as all other age groups of the population and, consequently, are at risk of brain damage. This works further illustrates the need for systematic iodine supplementation of the population in Belgium. Received: 19 September 2000 / Accepted: 11 October 2000     

Sensitivity of iodine deficiency indicators and iodine status in Turkey

BACKGROUND: Iodine deficiency is a major health problem worldwide. Goiter prevalence and the median urinary iodine concentration in a population usually define endemic iodine deficiency. In addition to goiter prevalence and median urinary concentration, thyroid stimulating hormone (TSH) and thyroxine have been used as iodine deficiency indicators. OBJECTIVE: To evaluate endemic goiter prevalence in Western Anatolia, Turkey, and to evaluate the sensitivity of thyroglobulin and height percentile as iodine deficiency indicators. SUBJECTS: We examined 727 school-children (378 girls, 349 boys) in two cities (Bolu and Düzce) and six mountainous rural areas, in West Anatolia. Of the 727 children, 234 were from four urban schools, and 493 were from eight rural schools. METHODS: Clinical examination and ultrasonography were used to evaluate goiter prevalence. Iodine in spot urine, serum total thyroxine (T4), serum free thyroxine (FT4), thyroid stimulating hormone (TSH), and thyroglobulin (Tg) were measured. Iodine deficiency severity was classified based on thyroid volume measurements by ultrasonography and urinary iodine excretion. RESULTS: The degree of iodine deficiency according to concentration of urinary iodine was severe in 276 children (38%), moderate in 151 (20.8%), mild in 114 (15.7%), and within normal levels in 186 (25.4%). Although urban areas showed normal or mild urinary iodine excretion, four rural areas showed from mild to severe iodine deficiency (p < 0.001). Thyroid volumes of the severe iodine deficiency group were significantly higher than those of moderate and mild iodine deficiency groups (p < 0.001). There was no significant difference between thyroid volumes in moderate and mild iodine deficiency groups. FT4 levels of the severe iodine deficiency group were significantly lower than in moderate and mild iodine deficiency groups (p < 0.001). There was no significant correlation between TSH and iodine excretion (r = 0.01, p > 0.05). Thyroglobulin (Tg) levels were significantly different between all groups (p < 0.001). There was a significant negative correlation between Tg and urinary iodine excretion (r = -0.27, p < 0.001). CONCLUSIONS: Severe and moderate iodine deficiency areas are more prevalent in Turkey than mild and normal iodine concentration areas. In addition to urinary iodine concentration and thyroid volume, height percentile and Tg are also sensitive markers for endemic iodine deficiency. TSH screening should be performed nationwide in Turkey. We recommend compulsory iodination of table and industrial salt.     

Overweight increases risk of first trimester hypothyroxinaemia in iodine‐deficient pregnant women

Hypothyroxinaemia early in pregnancy may impair fetal brain development. Increased body weight has been associated with low thyroxine concentrations in non‐pregnant women. In pregnant women, morbid maternal obesity is a risk factor for thyroid dysfunction. But whether lesser degrees of overweight that are much more common could be a risk factor for hypothyroxinaemia in pregnancy is unclear. The objective of this study was to investigate if overweight increases risk for thyroid dysfunction, and specifically hypothyroxinaemia, in iodine‐deficient pregnant women. We performed a cross‐sectional study at first hospital visit among healthy Thai pregnant women. We measured weight and height, urinary iodine concentration (UIC), serum thyroid hormones and thyroglobulin. Pre‐pregnancy weight and relevant dietary factors were determined by questionnaire, and body mass index (BMI) was used to classify weight status. Among 514 women (mean gestational age, 11 weeks) with a median UIC of 111 μg dL^–1, indicating mild iodine deficiency, 12% had low free thyroxine (fT4) concentrations: 3% had overt hypothyroidism; 7% had subclinical hypothyroidism; and 8% had isolated hypothyroxinaemia. Based on pre‐pregnancy BMI, 26% of women were overweight or obese. In a multiple regression model, BMI was a negative predictor of fT4 (β = ?0.20, P < 0.001). Compared to normal weight women, the prevalence ratio (95% CI) of a low fT4 in overweight women was 3.64 (2.08–6.37) (P < 0.01). Iodine‐deficient pregnant Thai women who are overweight have a 3.6‐fold higher risk of hypothyroxinaemia in the first trimester compared to normal weight women. Targeted screening should consider overweight a potential risk factor for thyroid dysfunction in pregnant women in iodine‐deficient areas.     

Iodine deficiency in Turkey

Turkey is an iodine deficiency area. The overall goitre prevalence is thought to be 30%, and most epidemiological studies give figures compatible with mild to moderate iodine deficiency. However, it is suspected that there are regions where iodine deficiency might be more severe than previously known. In this study the goitre prevalence and iodine status in a mountain village in Central Anatolia were investigated and the results compared to those of an urban area with mild iodine deficiency. Parameters of iodine status in the mountainous region showed severe iodine deficiency comparable to that in Central Africa. It seems that there are regions in Turkey where current programmes of salt iodization will be inadequate to correct the problem of iodine deficiency. Conclusions Our observations suggest that regional variations in iodine status may impede the success of salt iodization programmes, which alone may not be adequate for correction of the problem country-wide. Alternative sources of iodine should be considered in addition to expanded and more efficient salt iodization programmes. Received: 17 August 1998 / Accepted: 30 November 1998     

Thyroid function in pregnancy - maternal-fetal relationship in health and disease

The article reviews the changes in maternal and fetal thyroid function during pregnancy. During the first trimester the fetus is dependant on maternal thyroxine and later on the direct supply of iodine from the mother for its own thyroxine production. The placental deiodinase metabolism provides the fetus with additional iodine and protects the fetus from excessive iodothyronine transfer and enables the development of its own hypothalamic pituitary thyroid axis. Maternal and fetal hypothyroxinemia can lead to irreversible CNS damage. In autoimmune thyroid diseases immunoglobulins and goitrogenic drugs can cross the placenta and affect the fetal thyroid. Therefore, careful monitoring of maternal iodine supply, even in areas with mild to moderate iodine deficiency as well as iodine FT4 before and during pregnancy, and avoidance of unnecessary goitrogenic drugs is mandatory for optimal fetal growth and development. In cases where fetal hypothyroidism is diagnosed, intraamniotic T4 treatment is suggested.     

Neonatal hyperbilirubinemia and its association with thyroid hormone levels and urinary iodine excretion

Objective : To investigate, if, urinary iodine contents as a marker of iodine deficiency and hypothyroidism are associated with the incidence of neonatal hyperbilirubinemia.Methods : One hundred neonates with total serum bilirubin ≥15 mg/dl and with no known cause of jaundice were included in the study as a jaundice group. An equal number (n=100) of non-jaundiced neonates (bilirubin ≤14.9 mg/dl) with matching for age, gestation period and weight were enrolled in the study as a control group.Results : Thirteen neonates (13%) in the study group had urinary iodine levels < 100 mg/dl as against only 2 (2%) in the control group (p<0.05). Thirty-four (34/200-17%) neonates i.e. 17 each in the study and control groups had serum TSH> 5 mU/ml and hence an indirect indicator of iodine deficiency in the study population. The mean serum levels of total T3, T4 and TSH in the study neonates were 1.52 ±1.23 ng/ml, 15.8±12.0 μg/dl & 3.13 ±3.0 mU/ml respectively and did not differ significantly from the mean levels in the control group. Only one neonate in the study group had serum TSH > 20 mU/ml which was suggestive of hypothyroidism, but had normal T3 & T4. Seven neonates in the study group and 8 in the control group had low T4. There was no significant correlation between the maternal and neonatal urine iodine levels, thyroid functions and the bilirubin levels (p>0.01).Conclusion : The jaundiced babies had lower urine oidine levels than the control population. Since, there was no significant difference in the levels of the thyroid hormones, no cause and effect relationship could be inferred between iodine deficiency and jaundice.     

Influence of iodine supplementation on serum insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3) levels in severe iodine deficiency

Iodine deficiency is an important public health problem worldwide. In addition to severe consequences such as brain damage, developmental delay, deficits in hearing and learning, it also has a negative impact on growth. The negative impact of severe iodine deficiency (SID) on insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) was shown previously. In this study we aimed to analyze the impact of iodine supplementation on growth and growth factors of children with SID. One hundred and four children (63 boys and 41 girls) aged 5-15 years participated in the study. Height standard deviation scores (HSDS), and serum levels of IGF-I and IGFBP-3 were assessed both before and six months after a single dose of iodized oil. Serum levels of free thyroxine (FT4) and thyroid stimulating hormone (TSH) were also analysed to investigate the mechanisms by which alterations of iodine status may influence growth. Pubertal children had lower HSDS six months after iodine supplementation, while that of prepubertal children remained unchanged. IGF-I and IGFBP-3 levels decreased significantly and FT4 levels were suppressed six months after the supplementation, while TSH was normalized. These findings suggest a negative impact of iodine supplementation on growth factors in the short-term, which may be a direct effect of iodine repletion or an indirect effect caused by alterations in thyroid function. It may also be related to the method of supplementation used. Further studies are necessary to resolve these issues, as well as to examine the impact of iodine supplementation on growth in the long-term.     

Neonatal iodine deficiency: clinical aspects

Iodine is a trace element which is essential for the synthesis of thyroid hormones. The thyroid hormones, thyroxine (T4) and 3,5,3'-triiodothyronine (T3), are necessary for adequate growth and development throughout fetal and extrauterine life. The iodine intake of newborns is entirely dependent on the iodine content of breast milk and the formula preparations used to feed them. An inadequate iodine supply might be especially dangerous in the case of premature babies. The minimum recommended dietary allowance (RDA) for different age groups has recently been revised. The iodine intake required is at least 15 microg/kg/day in full-term infants and 30 microg/kg/day in preterms. The iodine content of many evaluated preparations for feeding premature infants appears to be inadequate. Premature infants are now in a situation of iodine deficiency, precisely at a stage of psychomotor and neural development which is extremely sensitive to alterations of thyroid function.     

Neonatal thyroid screening as a monitoring tool for the control of iodine deficiency

In conditions of iodine deficiency, the frequency distribution of neonatal thyroid-stimulating hormone (TSH) is shifted towards elevated values. Elevated serum TSH in the neonate indicates insufficient supply of thyroid hormones to the developing brain, and therefore constitutes the only indicator that allows prediction of brain damage, which is the main complication of iodine deficiency. This paper reviews studies on neonatal thyroid function in iodine deficiency and confirms the former statement by WHO/UNICEF/ICCIDD that the frequency of neonatal TSH above 5 mU/L blood is below 3% in conditions of normal iodine supply, that a frequency of 3-19.9% indicates mild iodine deficiency and that frequencies of 20-39.9% and above 40% indicate moderate to severe iodine deficiency, respectively. Neonatal thyroid screening appears as a particularly sensitive index in the monitoring of iodine supply at a population level.     

Neonatal thyroid screening as a monitoring tool for the control of iodine deficiency

In conditions of iodine deficiency, the frequency distribution of neonatal thyroid-stimulating hormone (TSH) is shifted towards elevated values. Elevated serum TSH in the neonate indicates insufficient supply of thyroid hormones to the developing brain, and therefore constitutes the only indicator that allows prediction of brain damage, which is the main complication of iodine deficiency. This paper reviews studies on neonatal thyroid function in iodine deficiency and confirms the former statement by WHO/UNICEF/ICCIDD that the frequency of neonatal TSH above 5 mU/L blood is below 3% in conditions of normal iodine supply, that a frequency of 3-19.9% indicates mild iodine deficiency and that frequencies of 20-39.9% and above 40% indicate moderate to severe iodine deficiency, respectively. Neonatal thyroid screening appears as a particularly sensitive index in the monitoring of iodine supply at a population level.     

Carence iodée : épidémiologie,conséquences,prophylaxie au cours de la grossesse et l'allaitement

Iodine intakes in humans are variable with age and physiologic status: in pregnant and lactating women, recommended iodine intakes are from 200 to 300 μg/day. Epidemiological studies in France demonstrate the presence of moderate iodine deficiency in the majority of pregnant and lactating women. This iodine deficiency induces maternal thyroid hyperplasia and then development of goiter in women, as well as impaired thyroid parameters. Maternal hypothyroxinemia during the first trimester of pregnancy can be associated with abnormal cognitive development and intellectual outcomes in the newborn and the children. According to the recent recommendations for the prevention and control of iodine deficiency in pregnant and lactating women from the World Health Organization, systematic iodine prophylaxis is indicated in France: 100 μg/day for women of reproductive age and 200 μg/day for pregnant and lactating women in order to eradicate iodine deficiency during pregnancy and lactation, and to prevent their maternal and fetal consequences.     

Assessment of goiter prevalence, iodine status and thyroid functions in school-age children of rural Yusufeli district in eastern Turkey

According to previous studies, Turkey has generally been accepted as a moderate endemic iodine deficient country. However, it has recently been reported that there are regions in Turkey where iodine deficiency is more severe than previously known. The current study was aimed at ascertaining the goiter prevalence by thyroid volumes, iodine status and thyroid functions in school-age children living in an area which is suspected to have moderate or severe iodine deficiency. Overall goiter was found in 47.6% of children, in 22.8% of girls and in 24.8% of boys. Mean thyroid volumes did not differ significantly according to sex. Significant correlation was found between thyroid volume and body surface area and age. There was a negative correlation between the urinary iodine concentration and thyroid volume (r = 0.45, p < 0.01). Median urinary iodine concentrations in subjects with and without goiter were 20 microg/dl and 5.2 microg/dl, respectively. While median urinary iodine levels of the subjects with goiter were consistent with severe-moderate iodine deficiency, levels in subjects without goiter were comparable to moderate-mild iodine deficiency. None of the subjects had the signs or symptoms of hyper-or hypothyroidism. The differences in the mean values of thyroid hormones and TSH levels between subjects with or without goiter were not significant (p > 0.05). No correlation was found between urinary iodine concentrations and thyroid hormone levels. A weak correlation was found between urinary iodine concentration and TSH levels (r = 0.12, p = 0.05). Individuals with goiter were investigated etiologically: biochemical hypothyroidism was detected in 2%, compensated hypothyroidism in 12.6%, autoimmune thyroiditis in 2%, nodular goiter in 3% and isolated high TSH level with autoimmune thyroiditis in 0.08%. In conclusion, although a salt iodization program has been started in Turkey, our study indicates that some regions with severe iodine deficiency are still present. This research suggests that this program should be re-evaluated for remote areas with self-contained economic systems, and should be expanded and more effectively applied nation-wide.     

Dysgenesis of thyroid is the common type of childhood hypothyroidism in environmentally iodine deficient areas of north India

Forty-five children (28 girls and 17 boys; mean age 4.5 years) with hypothyroidism referred to us from January 1989 to November 1990 were evaluated prospectively for the pattern of hypothyroidism by hormone assays, scintiscan and urinary iodine estimation. Among the 6 children from non-endemic areas, athyreosis and/or hypoplasia were seen in 3, ectopia in 2 and dyshormonogenesis in 1. Of 39 children from moderate to severe environmentally iodine deficient regions, 18 (46%) had athyreosis and/or hypoplasia and 10 (26%) ectopic thyroid. Iodine deficiency was seen in 4, dyshormonogenesis in 4, secondary/tertiary hypothyroidism in 2 and thyroiditis in 1. The mean age of these children at the onset of symptoms was 1.4 years and at clinical presentation 4.5 years. There was significant growth retardation with 54% of children being below the 5th centile of Indian standards. There was no significant difference in the age at onset of symptoms and presentation, clinical features and bone age for the different types. The levels of serum total T4 were significantly low in dysgenesis (athyreosis, hypoplasia and ectopia, p < 0,001). Dysgenesis of the thyroid is the most common type of childhood hypothyroidism in iodine deficiency endemias. We postulate that severe iodine deficiency in the intrauterine and early neonatal period may lead to dysgenesis of the thyroid.     

Intrauterine fatty acid accretion rates in human brain: implications for fatty acid requirements

Fatty acid components of infant brain were determined to assess fatty acid requirements for synthesis of structural lipids in brain tissue during the last trimester of development in the fetus. Quantitative fatty acid analysis of cerebellum, frontal and occipital brain lobes indicated rapid accretion of chain elongation and desaturation products during the last trimester of brain growth. Frontal and occipital brain lobes were similar in fatty acid content. Fatty acid accretion rates were determined by regression analysis of tissue fat components at varying gestational ages. Tissue accretion of saturated and ω-9 fatty acids, as well as total fatty acid content, paralleled increases in whole brain weight. Levels of linoleic (C_18:2, ω-6) and linolenic (C_18:2, ω-3) acids were consistently low in brain during the last trimester of development, while marked substantial accretion of long chain desaturation products, arachidonic (C_20:4, ω-6) and docosahexaenoic (C_22:6, ω-3) acids occurred. Accretion of individual fatty acids of cerebellum also reflected changes in tissue total fatty acid content, with exception of the levels of C_18:3, ω-3 and its chain elongation products present in cerebellum during the last trimester. These developmental changes and estimates of fatty acid incorporation into whole brain and cerebellum are quantitatively relevant to estimation of fatty acid requirements of the low birth weight neonate.     

Thyroid gland volume as measured by ultrasonography in preterm infants

The volume of the thyroid gland was determined by ultrasonography in 30 preterm infants (27-36 weeks' gestation) born in Madrid. Thyroid gland volume significantly increased (p < 0.01) with postnatal and postmenstrual age and was very well correlated with body weight, height and surface area (p < 0.01). Serum thyroid hormones 3,5,3'-triiodothyronine (T₃) and free thyroxine (FT₄) were linearly correlated with postnatal and postmenstrual age, thus T₃ and FT₄ levels were also correlated with thyroid gland volume (p < 0.05). We report measurements of the thyroid gland volume obtained by ultrasonography in this group of preterm infants. Quantitative determination of thyroid gland volume is more accurate for the diagnosis of goitre than clinical criteria. It is also interesting to determine the thyroid gland volume in the neonatal period when the thyroid is particularly hypersensitive to the effects of iodine deficiency and excess.     

Effects of low level radiation from the Chernobyl accident in a population with iodine deficiency

To determine the effects of low dose radiation from ¹³¹I and ¹³⁷Cs resulting from the Chernobyl disaster on the expression of endemic goiter in children, we studied children in regions with and without evidence of radiocontamination but comparable iodine insufficiency. We included 89 children in the study (radiocontaminated) region (SR) and 116 in the control region (CR) because they were either fetuses, infants, or pre-adolescents at the time of exposure. We evaluated thyroid dimensions by clinical examination and ultrasound; thyroid function by hormonal levels, and thyroglobulin measurement; histology of the thyroid by fine needle aspiration; and thyroid autoimmunity. SR subjects had 5 times the frequency of thyroid enlargement as those from CR, greatest in the younger patients. There were no instances of clinically apparent thyroid dysfunction. Antithyroid microsomal and antithyroglobulin antibodies were present in a markedly greater percentage of SR subjects. Fine needle biopsy demonstrated greater cellular proliferation in samples from SR. Conclusions We have demonstrated findings of autoimmune thyroid disease at markedly increased frequency in a population of children with poor iodine nutriture who were exposed to low level radiation, compared to a more iodine deficient population not so exposed. These results suggest that low level radiation may induce thyroid gland changes in children who have inadequate iodine intake nutriture and reinforce the importance of adequate dietary iodine. Received: 14 June 1996 / Accepted in revised form: 20 June 1997     

A case of familial thyroxine binding globulin excess associated with growth hormone deficiency

A 7 years 3 months old Japanese boy with familial thyroxine binding globulin (TBG) excess associated with growth hormone (GH) deficiency is reported. The patients height was 106.4 cm (- 2.86 s.d.) and his bone age was 5 years and 3 months. He had no goiter and his developmental milestones were normal. The serum thyroid stimulating hormone (TSH) was 2.8 μU/mL, triiodothyronine (T₃) 3.1 ng/mL, thyroxine (T₄) 23.4 μg/dL and free T₄ 1.8 ng/dL. The serum TBG level was beyond 80.0 μg/mL, with normal TSH response to the thyrotropin-releasing hormone (TRH) test. Familial study revealed that his grandmother, mother, uncle, younger sister and younger brother had high TBG and T₃ levels, thus an X-linked co-dominant transmission was suggested. The peak GH responses to insulin and clonidine hydrochloride were 5.8 and 8.2 ng/mL, respectively. The mean nocturnal GH concentration was 2.5 ng/mL. His growth velocity increased from 4.8 to 8.4 cm/year and his serum TBG levels decreased gradually after human growth hormone (hGH) treatment.     

Thyroid function in fullterm and preterm newborns

The development of the hypothalamic-pituitary-thyroid system in the fetus occurs through three phases: thyroid pituitary embryogenesis, maturation of hypothalamus, maturation of thyroid system, neuroendocrine control and T₄ tissue deiodination. Defects in early phases I and II lead to permanent disorders whereas abnormalities in phase III result in transient functional immaturities especially in preterms. Cord serum TSH, T₄ and T₃ were estimated in 450 newborns (390 full term>36 wk gestation and 60 preterms<36 wk). The mean cord TSH of 5·069±7·4 μ U/ml in full term was lower than 7·88±3·77 μ U/ml in preterms (P<0·01). The mean cord T₄ and T₃ were significantly higher (P<0·01) 9·716±6·44 μg/dl and 0·425±0·17 ng/ml in full term as compared to preterms 6·46±3·4 and 0·355±0·16 respectively. There was significant negative correlation of serum TSH (r=?0·84 and P<0·05) and positive correlation of serum T₄ (r=0·97, P<0·001) and T₃ (r=0·89, P<0·05) with gestational age. The relationship of these hormones to weight irrespective of gestational age was more significant when compared in newborns >3 kg and <2 kg rather than in all intermediate groups. No significant differences in these hormones were evident amongst the AGA and SGA infants above and below 36 weeks gestation. Transient hypothyroxinemia, and hyper-thyrotropinemia, transient primary hypothyroidism and low T₃ syndromes are some of the transient abnormalities of thyroid function and are more commonly encountered in preterms.     

Maternal iodine insufficiency and adverse pregnancy outcomes

This study aimed to assess the iodine status of pregnant women in each trimester and to compare the pregnancy outcomes between groups with iodine insufficiency and iodine sufficiency. Longitudinal study on urinary iodine concentration (UIC) in each trimester as well as comparison between women with iodine insufficiency (<150 mcg L^?1) and iodine sufficiency was conducted. Pregnant women without thyroid diseases who had not received iodine supplementation were recruited for UIC measurements in each trimester and were followed up for pregnancy outcomes. In the analysis of 384, 325 and 221 samples in the first, second and third trimester, the medians of UICs were 147.39, 157.01 and 153.07 mcg L^?1, respectively. Of 399 women, 174 (43.6%) had a UIC less than 150 mcg L^?1 (suggesting iodine insufficiency) and 225 (56.4%) had a UIC greater than or equal to 150 mcg L^?1 (suggesting iodine sufficiency). Of 390 women with availability of the final outcomes, 171 and 219 in the insufficiency and sufficiency group, respectively, the rates of preterm birth and low birthweight were significantly higher in the insufficiency group, 17.5% vs. 10.0% (P = 0.031) and 19.9% vs. 12.3% (P = 0.042), respectively. Logistic regression analysis showed that iodine status was an independent risk of preterm birth and low birthweight. Finally, women with a UIC <100 mcg L^?1 had a significantly higher rate of fetal growth restriction, 13/68 vs. 30/322 (P = 0.031). In northern Thailand, a great number of pregnant women had a median UIC less than 150 mcg L^?1 and they had a higher risk of preterm birth and low birthweight. Finally, those with a median UIC of less than 100 mcg L^?1 had a higher risk of fetal growth restriction.