Thyroid function parameters in normal pregnancies in an iodine sufficient population

Thyroid peroxidase antibody titers, thyroid function, and iodine nutrition status of pregnant normotensive and preeclamptic women in Eastern Cape South Africa

BACKGROUND

Autoimmune thyroid disease, one of the main risk factors for hypothyroidism, is associated with adverse pregnancy outcomes. The burden of autoimmune thyroid disease in pregnancy and its association with thyroid function among normotensive pregnant women and pregnant women with hypertension in South Africa are not known.

OBJECTIVE

This study aimed to establish the magnitude of thyroid peroxidase autoantibodies in pregnancy in the Eastern Cape of South Africa and its relationship with iodine nutrition status and preeclampsia.

STUDY DESIGN

Overall, 60 randomly selected normotensive pregnant controls at term and 120 pregnant participants with preeclampsia in the third trimester of pregnancy going to the Mthatha Regional Hospital and the Nelson Mandela Academic Hospital in the Eastern Cape Province who had complete data on thyroid peroxidase antibody titers, urinary iodine concentrations, serum thyroid-stimulating hormones, and free triiodothyronine, free thyroxine, and thyroglobulin levels were enrolled in this unmatched case-control study.

RESULTS

The cases and controls had similar mean chronological age (23.8 vs 24.0 years), body mass index (29.4 vs 28.8 kg/m2), and median parity (both 1) (P>.05). The controls had a higher mean gestational age than participants with preeclampsia (38.5 vs 33.7 weeks, respectively; P<.001). Both participants with preeclampsia and normotensive participants had median thyroid peroxidase antibody levels consistent with a negative thyroid autoimmune status. Participants with preeclampsia had higher but nonstatistically significant median thyroid peroxidase antibody (2.14 vs 1.77 IU/L), thyroglobulin (25.9 vs 21.3 µg/L), and thyroid-stimulating hormone (2.4 vs 2.3 mIU/L) levels (P>.05) and significantly lower median urinary iodine concentration (123.4 vs 188.6 µg/L), free thyroxine (13.2 vs 14.1 pmol/L), and free triiodothyronine (4.3 vs 4.6 pmol/L) levels (P<.05) than normotensive controls. Thyroid peroxidase antibodies were positively correlated with thyroglobulin, urinary iodine concentration, and thyroid-stimulating hormone.

CONCLUSION

In the rural Eastern Cape of South Africa, pregnant women in the third trimester of pregnancy have thyroid peroxidase antibody titers that show negative thyroid autoimmune status. Insufficient iodine intake, other than thyroid autoimmune disease, seems to be the underlying cause of the lower free triiodothyronine and free thyroxine levels observed among women with preeclampsia.

Evaluating thyroid function in pregnant women

Thyroid hormones are primarily responsible for regulating the basal metabolic rate but also make important contributions to reproductive function and fetal development. Both hyper- and hypothyroidism in pregnancy have been associated with increased risks of complications that include preeclampsia and low birth weight, among others. Furthermore, thyroid hormone deficiency in the developing fetus results in neurodevelopmental delay. As the fetus is exclusively reliant on maternal thyroid hormone for most of the first trimester and requires continued maternal supply until birth, identifying maternal thyroid dysfunction is critically important. However, evaluating thyroid function in pregnancy is challenging because of the many physiological changes that affect concentrations of thyroid-related analytes. Increasing plasma human chorionic gonadotropin (hCG) concentrations in the second half of the first trimester elicit a corresponding transient decrease in thyroid-stimulating hormone (TSH), and continually increasing estradiol concentrations throughout pregnancy cause substantial increases in thyroxine-binding globulin (TBG) and total thyroxine (T4) relative to the nonpregnant state. Lastly, free T4 concentrations gradually decrease with increasing gestational age. For these reasons, it is essential to interpret thyroid function test results in the context of trimester-specific reference intervals to avoid misclassification of thyroid status. This review summarizes the effects of thyroid dysfunction prior to conception and during pregnancy and describes considerations for the laboratory assessment of thyroid function in pregnant women.

Iodine deficiency in pregnancy along a concentration gradient is associated with increased severity of preeclampsia in rural Eastern Cape, South Africa

Background

Preeclampsia is a leading cause of maternal mortality and morbidity in South Africa. Iodine deficiency in pregnancy, which is amenable to correction through iodine supplementation, has been reported to increase the risk of preeclampsia. However, the association of iodine nutrition status with preeclampsia in South Africa has not been studied.

Methods

We enrolled 51 randomly selected normotensive pregnant controls at term together with 51 consecutively selected cases of preeclampsia and 51 cases of severe preeclampsia/eclampsia, all in the third trimester, from Mthatha Regional and Nelson Mandela Academic Hospital in the Eastern Cape Province. Urinary iodine concentration (UIC), serum thyroid-stimulating hormone (TSH), triiodothyronine (FT3), thyroxine (FT4) and thyroglobulin (Tg) levels were compared between cases and controls.

Results

The respective chronological and gestational ages at enrolment for normotensive, preeclampsia and severe preeclampsia/eclampsia participants were: age 23, 24 and 19 years (p = 0.001), and gestational age 38, 34, and 35 weeks (p < 0.001). The median gravidity was 1 for all three groups. The median UIC, FT4, FT3 revealed a decreasing and Tg a rising trend with the severity of preeclampsia (p < 0.05). TSH had a non-significant rising trend (p > 0.05). The respective median values for normotensive, preeclampsia and severe preeclampsia/eclampsia participants were UIC 217.1, 127.7, and 98.8 μg/L; FT4 14.2, 13.7, and 12. pmol/L; FT3 4.8, 4.4, and 4.0 pmol//L; Tg 19.4, 21.4, and 32. Nine microgram per liter; TSH 2.3, 2.3, and 2.5 mIU/L. UIC < 100 μg/L, Tg > 16 μg/L and FT4 < 11.3 pmol/L were independent predictors of preeclampsia/eclampsia syndrome.

Conclusion

Women with severe preeclampsia/eclampsia had significantly low UIC and high Tg, suggesting protracted inadequate iodine intake. Inadequate iodine intake during pregnancy severe enough to cause elevated Tg and FT4 deficiency was associated with an increased risk of severe preeclampsia/eclampsia.

Practical Guidelines for Diagnosing and Treating Thyroid Disease Based on the WOMED Metabolic Model of Disease Focusing on Glycolysis and Coenzyme Q10 Deficiency—A Clinical Alternative to the 2021 Retired Clinical Practice Guidelines of the Endocrine Society

This review aims to provide a functional, metabolic view of the pathogenesis of benign thyroid disease. Here, we summarize the features of our previous publications on the “WOMED model of benign thyroid disease”. As of 2021, the current state of art indicates that the basic alteration in benign thyroid disease is a metabolic switch to glycolysis, which can be recognized using 3D-power Doppler ultrasound. A specific perfusion pattern showing enlarged vessels can be found using this technology. This switch originates from an altered function of Complex I due to acquired coenzyme Q₁₀ deficiency, which leads to a glycolytic state of metabolism together with increased angiogenesis. Implementing a combined supplementation strategy that includes magnesium, selenium, and CoQ₁₀, the morphological and perfusion changes of the thyroid can be reverted, i.e., the metabolic state returns to oxidative phosphorylation. Normalization of iron levels when ferritin is lower than 50 ng/mL is also imperative. We propose that a modern investigation of probable thyroid disease requires the use of 3D-power Doppler sonography to recognize the true metabolic situation of the gland. Blood levels of magnesium, selenium, CoQ₁₀, and ferritin should be monitored. Thyroid function tests are complementary so that hypo- or hyperthyroidism can be recognized. Single TSH determinations do not reflect the glycolytic state.

Mildly elevated thyroid-stimulating hormone is associated with endothelial dysfunction and severe preeclampsia among pregnant women with insufficient iodine intake in Eastern Cape province, South Africa

BACKGROUND

Preeclampsia and hypothyroidism are associated with endothelial dysfunction. Iodine deficiency is a risk factor for subclinical hypothyroidism in pregnancy. However, there is a paucity of data on the relationship between iodine nutrition state in pregnancy, the degree of endothelial dysfunction, and the risk of preeclampsia.

METHODS

Ninety-five normotensive pregnant women, 50 women with preeclampsia with no severe features, and 50 women with severe preeclampsia were enrolled into the current study from the maternity units of Nelson Mandela Academic Hospital and Mthatha Regional Hospitals in Eastern Cape Province, South Africa. Urinary iodine concentration (UIC), serum markers of thyroid function, aortic augmentation index, and pulse wave velocity (PWV) were compared.

RESULTS

Median UIC was 167.5, 127.7, and 88.5 µg/L, respectively for normotensive pregnant women, those with preeclampsia and severe preeclampsia (p = .150). Participants with severe preeclampsia had significantly higher median thyroid-stimulating hormone (TSH) and oxidized LDL than normotensive and preeclamptic women without severe features (respectively 3.0, 2.3, and 2.3 IU/L; 1.2, 1.0, and 1.0 IU/L, p < .05). The median Aortic augmentation index was 7.5, 19.0, and 21.0 (p < .001), and the pulse wave velocity 5.1, 5.7, and 6.3, respectively for normotensive, preeclampsia, and severe preeclampsia participants (both p < .001). In linear regressions, TSH, age, and hypertensive disease were independent predictors of elevated PWV.

CONCLUSION

Upper normal-range TSH levels in women with severe preeclampsia were associated with markers of endothelial dysfunction. The low UIC and trend towards the elevation of thyroglobulin suggest that inadequate iodine intake may have increased TSH levels and indirectly caused endothelial dysfunction.

A longitudinal study of thyroid markers during pregnancy and the risk of gestational diabetes mellitus and post-partum glucose metabolism

AIMS

To determine the relationship between thyroid markers during pregnancy and gestational diabetes mellitus (GDM) or post-partum glucose metabolism.

MATERIALS AND METHODS

Based on pregnancy 75-g oral glucose tolerance test (OGTT) results, 1467 subjects were grouped into normal glucose tolerance (NGTp; n = 768) and GDM (n = 699) groups. Furthermore, based on post-partum 75-g OGTT results, 286 GDM subjects, screened for glucose metabolism after delivery, were grouped into NGTd (n = 241) and abnormal glucose tolerance (AGT; n = 45) groups.

RESULTS

Maternal age, family history of diabetes, acanthosis nigricans, previous adverse pregnancy outcomes and caesarean section incidence, and thyroid positive antibody rates were higher in the GDM group than in the NGTp group. In the first trimester, free triiodothyronine (FT3), thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) levels were higher in the GDM group than in the NGTp group. In the second trimester, free thyroxine (FT4) levels were lower and TPOAb and TgAb levels were higher in the GDM group than in the NGTp group. After adjusting for confounding factors, FT3, TPOAb and TgAb (first trimester), and FT4, TPOAb and TgAb (second trimester) were risk factors for GDM. TPOAb and TgAb levels were higher in the AGT group than in the NGTd group and were potential predictors of abnormal post-partum glucose tolerance.

CONCLUSIONS

GDM risk significantly increased with increased FT3 (first trimester), TPOAb and TgAb (first and second trimesters) or with decreased FT4 (second trimester). Presence of thyroid antibodies predicted post-partum glucose abnormalities in subjects with GDM.

Development of Gestational Age-Specific Thyroid Function Test Reference Intervals in Four Analytic Platforms Through Multilevel Modeling

Background: A population-based reference interval (RI) of thyroid hormones in pregnancy using a standardized methodology is crucial for clinicians to make accurate diagnoses and important for the comparison of test results obtained from different analytic platforms. Methods: We enrolled 600 healthy Chinese women to obtain longitudinal serum samples across gestation, after exclusion of subjects with antibodies to thyroid peroxidase, thyroglobulin or thyrotropin receptor. Gestational age-specific RIs were constructed by using polynomial regression equations with MLwiN. Results: Free thyroxine (fT4) levels rose to a peak at the 7th-8th gestational weeks and then declined gradually till 28th week, while thyrotropin (TSH) level decreased from early pregnancy to a nadir at the 9th week. The data support the recent notion by the American Thyroid Association to raise the TSH upper RI to 4.0 mIU/L. We also demonstrate that thyroid hormone reference ranges are not affected in a mildly iodine-deficient population and by including women with the presence of antibodies against thyroid peroxidase and thyroglobulin who are otherwise healthy. Conclusions: The study highlights a methodology in constructing gestational age-specific thyroid function test RIs on different analytic platforms to provide a better interpretation and comparison of results obtained across different platforms.

Applications for non-invasive thyroid hormone measurements in mammalian ecology, growth, and maintenance

Thyroid hormones (THs) play a pivotal role in the regulation of metabolic activity throughout all life stages. Cross-talk with other hormone systems permits THs to coordinate metabolic changes as well as modifications in growth and maintenance in response to changing environmental conditions. The scope of this review is to explain the relevant basics of TH endocrinology, highlight pertinent topics that have been investigated so far, and offer guidance on measuring THs in non-invasively collected matrices. The first part of the review provides an overview of TH biochemistry, which is necessary to understand and interpret the findings of existing studies and to apply non-invasive TH monitoring. The second part focuses on the role of THs in mammalian ecology, and the third part highlights the role of THs in growth and maintenance. The fourth part deals with the advantages and difficulties of measuring THs in non-invasively collected samples. This review concludes with a summary that considers future directions in the study of THs.

A Longitudinal Study of Thyroid Markers Across Pregnancy and the Risk of Gestational Diabetes

CONTEXT

T3 is the biologically active thyroid hormone involved in glucose metabolism. The free T3 (fT3)/free T4 (fT4) ratio, a marker indicating conversion of fT4 to fT3, is also implicated in glucose homeostasis.

OBJECTIVE

To examine associations of fT3 and the fT3/fT4 ratio with gestational diabetes mellitus (GDM).

DESIGN

In a case-control study, thyroid markers (fT3, fT4, TSH) were measured and the fT3/fT4 ratio was derived across four visits in pregnancy, including first (gestational weeks 10 to 14) and second (weeks 15 to 26) trimester. Conditional logistic regression adjusting for thyroid autoimmunity status and major GDM risk factors estimated trimester-specific associations of thyroid markers with subsequent GDM risk.

SETTING

Twelve US clinical centers.

PARTICIPANTS

One hundred seven GDM cases and 214 non-GDM controls from a multiracial pregnancy cohort of 2802 women.

MAIN OUTCOME MEASURES

GDM diagnosis ascertained from medical records.

RESULTS

Both fT3 and the fT3/fT4 ratio were positively associated with GDM: adjusted OR (95% CI) comparing the highest vs lowest fT3 quartile was 4.25 (1.67, 10.80) at the first trimester and 3.89 (1.50, 10.10) at the second trimester. Similarly, the corresponding risk estimates for the fT3/fT4 ratio were 8.63 (2.87, 26.00) and 13.60 (3.97, 46.30) at the first and second trimester, respectively. Neither TSH nor fT4 was significantly associated with GDM.

CONCLUSIONS

Higher fT3 levels, potentially resulting from de novo synthesis or increased fT4 to fT3 conversion, may be an indicator of GDM risk starting early in pregnancy.

Comparative analysis of thyroid function parameters in pregnant women

The aim of the present study was to investigate the serum levels of free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone (TSH) during pregnancy and comparative analysis of serum markers levels in non-pregnant women and pregnant women. Pregnant women were divided into four groups according to their gestational age: 8-14, 15-20, 21-36 and ≥37 weeks. Non-pregnant women were divided into three groups according to their age: 20-40, 41-55 and 56-85 years, and women of reproductive age (20-40 years) as control, which match their age and body mass index with pregnant women. The levels of serum markers were measured by magnetic microparticle chemiluminescence immunoassay and compared among different gestational weeks or with the control. In pregnant women, from 8-14 to ≥37 weeks, FT3 and FT4 levels declined, and significant differences were identified between each group, except for FT4 at 21-36 weeks, when compared with ≥37 weeks. While TSH was increased and significant differences were identified between each group. Compared with the control group, the concentrations of FT3, FT4 and TSH were lower in pregnant women for all weeks except for TSH in ≥37 weeks. Reference intervals of FT3, FT4 and TSH in pregnant women are much lower than that of the control women. Pregnant women are likely to have lower thyroid hormone levels throughout pregnancy. The current reference intervals of thyroid hormones were not feasible for pregnant women and pregnancy-specific reference intervals should be established according to a local Chinese pregnant women database.

A post-publication analysis of the idealized upper reference value of 2.5 mIU/L for TSH: Time to support the thyroid axis with magnesium and iron especially in the setting of reproduction medicine

Laboratory medicine approaches the evaluation of thyroid function mostly through the single determination of the blood level of thyroid stimulating hormone (TSH). Some authors have suggested an upper reference value for TSH of 2.5 mIU/L. This suggestion has not been confirmed by recent clinical studies. These studies have delivered a clinically valid reference range going from 0.3 to 3.5 mIU/L. These values are valid for both for the general population as well as in the setting of fertility and pregnancy. Current biochemical evidence about the elements required to maintain thyroid function shows that these not only include dietary iodine but also magnesium, iron, selenium and coenzyme Q10. Iron is important for the synthesis of thyroid peroxidase; magnesium-ATP contributes to the active process of iodine uptake; iodine has to be sufficiently present in the diet; selenium acts through selenoproteins to protect the thyroid cell during hormone synthesis and in deiodination of thyroxine; coenzyme Q10 influences thyroid vascularity. As a consequence, good clinical practice requires additional biochemical information on the blood levels of magnesium, selenium, coenzyme Q10 as well as iron status. Since these elements are also important for the maintenance of reproductive function, we postulate that they constitute the connecting link between both endocrine systems.

Multifactorial determinants of cognition - Thyroid function is not the only one

Background

Since the 1960s hypothyroidism together with iodine deficiency have been considered to be a principal determinant of cognition development. Following iodine supplementation programs and improved treatment options for hypothyroidism this relation might not be valid in 2015. On the other hand neurosciences have added different inputs also related to cognition.

Scope of review

We will examine the characteristics of the original and current publications on thyroid function and cognition and also add some general determinants of intelligence and cognition. One central issue for us is the relation of stress to cognition knowing that both physical and psychological stress, are frequent elements in subjects with thyroid dysfunction. We have considered a special type of stress called pre-natal stress which can influence cognitive functions. Fear and anxiety can be intermingled requiring mechanisms of fear extinction.

Major conclusions

Recent studies have failed to show an influence of thyroid medication during pregnancy on intellectual development. Neuroscience offers a better explanation of cognition than hypothyroidism and iodine deficiency. Additional factors relevant to cognition are nutrition, infection, prenatal stress, and early life stress. In turn stress is related to low magnesium levels. Magnesium supplementation can correct both latent hypothyroidism and acquired mild cognitive deficits.

General significance

Cognition is a complex process that depends on many determinants and not only on thyroid function. Magnesium deficiency appears to be a basic mechanism for changes in thyroid function as well as of cognition.

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Untreated hypothyroidism, i.e. hypothyroxinemia, can influence IQ.

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Thyroxine administration to euthyroid pregnant women has no effect on cognition.

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The hippocampus and NMDA receptors play a central role in cognitive processes.

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Antenatal and early life stressors can influence cognition later in life.

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Stressors can lead to decreased levels of magnesium and demands supplementation.