Iodine Supplementation throughout Pregnancy Does Not Prevent the Drop in FT4 in the Second and Third Trimesters in Women with Normal Initial Thyroid Function

Brucker‐Davis, Françoise; Panaïa‐Ferrari, Patricia; Gal, Jocelyn; Fénichel, Patrick; Hiéronimus, S.

doi:10.1159/000350882

Cited by 18 publications

(34 citation statements)

References 35 publications

(64 reference statements)

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“…Uncertainty also prevails in terms of the free T4 reference range during pregnancy, free T4 being associated with tT4. In one study [42], free T4 decreased from first to second trimester despite iodine supplementation and TSH remained stable, suggesting the decrease in free T4 during pregnancy may be a physiological observation. The same trend during pregnancy was observed in our study population regarding isolated hypothyroxinemia; the opposite trend, though in lower prevalence, was noticed in isolated hyperthyroxenemia, which was more frequent in first trimester (8%) than in third trimester (3%), highlighting the need of proper reference intervals deriving from a thyroid healthy, iodine sufficient population of pregnant women.…”

Section: Discussionmentioning

confidence: 96%

“…Several observational studies suggest an association between mild iodine deficiency during fetal life and poor educational level, motor skills, or verbal abilities in children 3-12 years of age [5,6,44,45]. However, this was not confirmed in randomized controlled trials of iodine supplementation of pregnant women with mild iodine deficiency [8,42], possibly due to lower than expected prevalence of iodine deficiency in the population studied in one trial [8] or due to low sample size in the other trial [42]. At the same time, other observational studies have indicated the opposite, i.e.…”

Section: Discussionmentioning

confidence: 99%

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Iodine deficiency in pregnant women in Sweden: a national cross-sectional study

et al. 2019

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Purpose Voluntary salt iodization at 50 mg/kg salt ensures adequate iodine nutrition in Swedish school-aged children, but iodine status in pregnant women is uncertain. Methods We conducted a cross-sectional national study of 743 pregnant women, at median gestational age of 23 weeks (IQR 9, 38), recruited from maternal health care centers. We measured: urinary iodine concentration (UIC) and urinary creatinine concentration in spot urine samples; thyroglobulin (Tg), thyroid-stimulating hormone (TSH), and total thyroxine (tT4) on dried blood spots (DBS); and thyreoperoxidase antibodies in serum samples. Data on dietary supplement use were obtained, and women were classified as supplement users (consuming multivitamins containing ≥ 150 µg iodine/day) and non-supplement users (no supplements or < 150 µg iodine/day from supplements). Results Overall median UIC [bootstrapped 95% confidence interval (CI)] was 101 µg/L (95, 108; n = 737): 149 µg/L (132, 164) in supplement users (n = 253) and 85 µg/L (79, 92) in non-supplement users (n = 440) (p < 0.001). Overall geometric mean DBS-Tg (95% CI) was 22.1 μg/L (20.8, 23.5; n = 675) and the prevalence of elevated DBS-Tg was 19%. DBS-Tg was lower in supplement users (n = 229) than in non-supplement users (n = 405) (19.1 vs 24.4 μg/L, p < 0.001). DBS-TSH, DBS-tT4, and S-TPOab positivity did not differ between the two groups. Conclusions Pregnant women in Sweden have inadequate iodine nutrition. Women not taking iodine supplements containing ≥ 150 µg iodine/day are affected by mild iodine deficiency and are at higher risk for increased thyroid activity, while maintaining euthyroidism. Iodine intake should be improved in women both before and after conception by promotion of iodized salt instead of non-iodized salt. We urge regular monitoring of iodine status in the general Swedish population, as well as in risk groups.

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Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

Iodine deficiency in pregnant women in Sweden: a national cross-sectional study

et al. 2019

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“…This may be caused by the increased transfer of iodine into the foetus in the second and third trimester. Though it has previously been shown that iodine supplementation can prevent this UIC decrease over the course of gestation, multivitamin supplementation in China should not contain iodine with the concern of iodine excess because mandatory USI was implemented in China. As a result, a decrease of UIC across trimesters was found in our study, which was corresponding to the decrease of SIC.…”

Section: Discussionmentioning

confidence: 99%

Serum iodine concentration in pregnant women and its association with urinary iodine concentration and thyroid function

Pan

Cui

Chen

et al. 2019

Clinical Endocrinology

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Summary Objective This study aims to evaluate the association of serum iodine concentration (SIC) with urinary iodine concentration (UIC) and thyroid function in pregnant women, as well as to provide the reference range of SIC of pregnant women in iodine‐sufficiency area. Methods Pregnant women were enrolled in the Department of Obstetrics, Tanggu Maternity Hospital, Tianjin from March 2016 to May 2017. Fasting venous blood and spot urine samples were collected. Serum free triiodothyronine (FT3), free thyroxine (FT4), thyroid‐stimulating hormone (TSH), thyroglobulin (Tg), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), UIC and SIC were measured. Results One thousand and ninety‐nine participants were included in this study. The median UIC was 156 μg/L. The median SIC was 108 μg/L, and the 95% reference interval for SIC was 65.6‐164.7 μg/L. SIC was positively correlated with UIC (r = 0.12, P < 0.001), FT3 (r = 0.23, P < 0.001), and FT4 (r = 0.50, P < 0.001) and was inversely correlated with TSH (r = −0.14, P < 0.001). Pregnant women with a SIC < 79.9 μg/L had a higher risk of hypothyroxinemia compared to those with higher SIC (OR = 2.44, 95% CI: 1.31‐4.75). Those having SIC > 138.5 μg/L were more likely to have thyrotoxicosis than those with lower SIC values (OR = 13.52, 95% CI: 4.21‐43.36). Conclusions Serum iodine level is associated with UIC and thyroid function in pregnant women. Low SIC was associated with increased risk for iodine deficiency and hypothyroxinemia, while high SIC was related to excess and thyrotoxicosis.

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“…Hypothyroxinemia is common in areas of iodine deficiency (40). Nonetheless, in iodine sufficient areas, controlled trials have not found any evidence that additional iodine supplementation reduces the risk of maternal hypothyroxinemia (40, 41). In Finland, pregnant women have adequate iodine levels because this nutrient is routinely supplemented in dietary salt (42).…”

Section: Discussionmentioning

confidence: 99%

Hypothyroxinemia During Gestation and Offspring Schizophrenia in a National Birth Cohort

Gyllenberg

Sourander²,

Surcel

et al. 2016

Biological Psychiatry

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Background Evidence from animal and human studies indicates that thyroid hormone deficiency during early gestation alters brain development. As schizophrenia is associated with prenatal brain insults and premorbid cognitive deficits, we tested the a priori hypothesis that serologically defined maternal thyroid deficiency during early to mid-gestation is associated with offspring schizophrenia. Methods The investigation is based on the Finnish Prenatal Study of Schizophrenia (FiPS-S), a nested case-control study that included archived maternal sera from virtually all pregnancies since 1983 (total N over 1 million). We identified all offspring in the cohort diagnosed with schizophrenia based on the national inpatient and outpatient register and matched them to comparison subjects (1:1) from the cohort on sex, date of birth, and residence in Finland at time of onset of the case. Maternal sera on 1010 case-control pairs were assessed for free thyroxine (fT4) and 948 for thyroid stimulating hormone (TSH). Results Maternal hypothyroxinemia (fT4≤10th percentile, normal TSH) was associated with an increased odds of schizophrenia (OR=1.75, 95% CI=1.22 – 2.50; p=0.002). When adjusted for maternal psychiatric history, province of birth and maternal smoking during pregnancy, the association remained significant (OR=1.70, 95%CI 1.13 – 2.55; p=0.010). Conclusions In a large, national birth cohort, prospectively documented early to mid-gestational hypothyroxinemia was associated with increased odds of schizophrenia in offspring. This can inform translational studies of maternal hypothyroxinemia examining molecular and cellular deviations relevant to schizophrenia.

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Iodine Supplementation throughout Pregnancy Does Not Prevent the Drop in FT4 in the Second and Third Trimesters in Women with Normal Initial Thyroid Function

Cited by 18 publications

References 35 publications

Iodine deficiency in pregnant women in Sweden: a national cross-sectional study

Iodine deficiency in pregnant women in Sweden: a national cross-sectional study

Serum iodine concentration in pregnant women and its association with urinary iodine concentration and thyroid function

Hypothyroxinemia During Gestation and Offspring Schizophrenia in a National Birth Cohort

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