Circulating thyroid hormone concentrations and placental thyroid hormone receptor expression in normal human pregnancy and pregnancy complicated by intrauterine growth restriction (IUGR)

Thyroid hormone analogues: Promising therapeutic avenues to improve the neurodevelopmental outcomes of intrauterine growth restriction

Intrauterine growth restriction (IUGR) is a pregnancy complication impairing fetal growth and development. The compromised development is often attributed to disruptions of oxygen and nutrient supply from the placenta, resulting in a number of unfavourable physiological outcomes with impaired brain and organ growth. IUGR is associated with compromised development of both grey and white matter, predisposing the infant to adverse neurodevelopmental outcomes, including long-lasting cognitive and motor difficulties. Cerebral thyroid hormone (TH) signalling, which plays a crucial role in regulating white and grey matter development, is dysregulated in IUGR, potentially contributing to the neurodevelopmental delays associated with this condition. Notably, one of the major TH transporters, monocarboxylate transporter-8 (MCT8), is deficient in the fetal IUGR brain. Currently, no effective treatment to prevent or reverse IUGR exists. Management strategies involve close antenatal monitoring, management of maternal risk factors if present and early delivery if IUGR is found to be severe or worsening in utero. The overall goal is to determine the most appropriate time for delivery, balancing the risks of preterm birth with further fetal compromise due to IUGR. Drug candidates have shown either adverse effects or little to no benefits in this vulnerable population, urging further preclinical and clinical investigation to establish effective therapies. In this review, we discuss the major neuropathology of IUGR driven by uteroplacental insufficiency and the concomitant long-term neurobehavioural impairments in individuals born IUGR. Importantly, we review the existing clinical and preclinical literature on cerebral TH signalling deficits, particularly the impaired expression of MCT8 and their correlation with IUGR. Lastly, we discuss the current evidence on MCT8-independent TH analogues which mimic the brain actions of THs by being metabolised in a similar manner as promising, albeit underappreciated approaches to promote grey and white matter development and improve the neurobehavioural outcomes following IUGR.

The Association between Infant Birth Weight, Head Circumference, and Neurodevelopmental Outcomes

OBJECTIVE

 The aim of this study was to evaluate whether being small for gestational age (SGA) or large for gestational age (LGA) or having a small or large head circumference (HC) at birth is associated with adverse neurodevelopmental outcomes.

STUDY DESIGN

 This is a secondary analysis of a multicenter negative randomized trial of thyroxine therapy for subclinical hypothyroid disorders in pregnancy. The primary outcome was child intelligence quotient (IQ) at 5 years of age. Secondary outcomes included several neurodevelopmental measures. Associations between the outcomes in children with SGA (<10th percentile) or LGA (>90th percentile) birth weights, using ethnicity- and sex-specific population nomogram as well as nomograms from the National Fetal Growth (NFG) study, were compared with the referent of those with appropriate for gestational age (AGA) birth weight. Similar analyses were performed for HC.

RESULTS

 Using the population nomogram, 90 (8.2%) were SGA and 112 (10.2%) were LGA. SGA neonates were more likely to be born preterm to mothers who were younger, smoked, and were less likely to have less than a high school education, whereas LGA neonates were more likely to be born to mothers who were older and have higher body mass index, compared with AGA neonates. SGA at birth was associated with a decrease in the child IQ at 5 years of age by 3.34 (95% confidence interval [CI], 0.54-6.14) points, and an increase in odds of child with an IQ < 85 (adjusted odds ratio [aOR], 1.9; 95% CI, 1.1-3.2). There was no association between SGA and other secondary outcomes, or between LGA and the primary or secondary outcomes. Using the NFG standards, SGA at birth remained associated with a decrease in the child IQ at 5 years of age by 3.14 (95% CI, 0.22-6.05) points and higher odds of an IQ < 85 (aOR, 2.3; 95% CI, 1.3-4.1), but none of the other secondary outcomes. HC was not associated with the primary outcome, and there were no consistent associations of these standards with the secondary outcomes.

CONCLUSION

 In this cohort of pregnant individuals with hypothyroid disorders, SGA birth weight was associated with a decrease in child IQ and greater odds of child IQ < 85 at 5 years of age. Using a fetal growth standard did not appear to improve the detection of newborns at risk of adverse neurodevelopment.

Sex-Specific Alterations in Placental Proteomics Induced by Intrauterine Hyperglycemia

Gestational diabetes mellitus (GDM) with intrauterine hyperglycemia induces a series of changes in the placenta, which have adverse effects on both the mother and the fetus. The aim of this study was to investigate the changes in the placenta in GDM and its gender differences. In this study, we established an intrauterine hyperglycemia model using ICR mice. We collected placental specimens from mice before birth for histological observation, along with tandem mass tag (TMT)-labeled proteomic analysis, which was stratified by sex. When the analysis was not segregated by sex, the GDM group showed 208 upregulated and 225 downregulated proteins in the placenta, primarily within the extracellular matrix and mitochondria. Altered biological processes included cholesterol metabolism and oxidative stress responses. After stratification by sex, the male subgroup showed a heightened tendency for immune-related pathway alterations, whereas the female subgroup manifested changes in branched-chain amino acid metabolism. Our study suggests that the observed sex differences in placental protein expression may explain the differential impact of GDM on offspring.

Labour and premature delivery differentially affect the expression of the endocannabinoid system in the human placenta

Plasma concentrations of N-arachidonyletholamine (AEA), N-oleoylethanolamide (OEA) and N-palmitoylethanolamide (PEA) increase at term and can predict when a woman is likely to go into labour. We hypothesised that increased plasma AEA concentrations in women in preterm and term labour might also be increased and have a function in the placenta at the end of pregnancy. Here we examined the expression of the N-acylethanolamine-modulating enzymes fatty acid amide hydrolase (FAAH) and N-acyl-phosphatidylethanolamine-specific phospholipase-D (NAPE-PLD) and of the cannabinoid receptors (CB1 and CB2) in the placenta and their activation in an in vitro model of the third-trimester placenta to determine if those expressions change with labour and have functional significance. Expression of CB1, CB2, FAAH and NAPE-PLD was examined by immunohistochemistry (IHC) and RT-qPCR in placental samples obtained from four patient groups: preterm not in labour (PTNL), term not in labour (TNL), preterm in labour (PTL) and term in labour (TL). Additionally, the effects of AEA on a third-trimester human cell line (TCL-1) were evaluated. All ECS components were present in the third-trimester placenta, with NAPE-PLD and CB2 being the key modulated proteins in terms of expression. Functionally, AEA reduced TCL-1 cell numbers through the actions of the CB2 receptor whilst CB1 maintained placental integrity through the expression of the transcription regulators histone deacetylase 3, thyroid hormone receptor β 1 and the modulation of 5α reductase type 1. The placenta in the third trimester and at term is different from the placenta in the first trimester with respect to the expression of CB1, CB2, FAAH and NAPE-PLD, and the expression of these proteins is affected by labour. These data suggest that early perturbation of some ECS components in the placenta may cause AEA-induced PTL and thus PTB.

Exogenous corticosterone administration during pregnancy in mice alters placental and fetal thyroid hormone availability in females

INTRODUCTION

Maternal prenatal psychological stress is associated with adverse pregnancy outcomes and increased risk of adverse health outcomes in children. While the molecular mechanisms that govern these associations has not been fully teased apart, stress-induced changes in placental function can drive sex-specific phenotypes in offspring. We sought to identify and examine molecular pathways in the placenta that are altered in response to maternal prenatal stress.

METHODS

We previously employed a mouse model of maternal prenatal stress where pregnant dams were treated with stress hormone (CORT) beginning in mid-gestation. Using this model, we conducted RNAseq analysis of whole placenta at E18.5. We used qRT-PCR to validate gene expression changes in the placenta and in a trophoblast cell line. ELISAs were used to measure the abundance of thyroid hormones in maternal and fetal serum and in the placenta.

RESULTS

Dio2 was amongst the top differentially expressed genes in response to exogenous stress hormone. Dio2 expression was more downregulated in placenta of female fetuses from CORT-treated dams than both control placenta from females and placenta from male fetuses. Consistent with Dio2's role in production of bioactive thyroid hormone (T3), we found that there was a reduction of T3 in placenta and serum of female embryos from CORT-treated dams at E18.5. Both T3 and T4 were reduced in the fetal compartment of the placenta of female fetuses from CORT-treated dams at E16.5. Exogenous stress hormone induced reduction in thyroid hormone in females was independent of circulating levels of TH in the dams.

DISCUSSION

The placental thyroid hormone synthesis pathway may be a target of elevated maternal stress hormone and modulate fetal programming of health and disease of offspring in a sex-specific fashion.

Maternal hypothyroidism in rats impairs placental nutrient transporter expression, increases labyrinth zone size, and impairs fetal growth

INTRODUCTION

Hypothyroidism during pregnancy is associated with fetal growth restriction (FGR). FGR is commonly caused by placental insufficiency and yet the role of hypothyroidism in placental regulation of fetal growth is unknown. This study aimed to investigate the effects of maternal hypothyroidism on placental nutrient transporter expression, placental morphology, and placental metabolism.

METHODS

Hypothyroidism was induced in female Sprague-Dawley rats by adding methimazole (MMI) to drinking water at moderate (MOD, MMI at 0.005% w/v) and severe (SEV, MMI at 0.02% w/v) doses from one week prior to pregnancy and throughout gestation. Maternal and fetal tissues were collected on embryonic day 20 (E20).

RESULTS

Hypothyroidism reduced fetal weight (PTrt<0.001) despite causing fetal hyperglycaemia (PTrt = 0.016). Placental weight was not affected by hypothyroidism however placental efficiency was reduced (PTrt<0.001), as was the junctional zone (JZ):labyrinth zone (LZ) weight ratio (PTrt = 0.005). LZ glycogen content was increased (PTrt = 0.029) and while mRNA expression of glucose transporters was reduced by hypothyroidism, only GLUT1 protein expression was reduced in male LZs. Maternal hypothyroidism reduced mitochondrial content (PTrt = 0.031), particularly in SEV males relative to CON males (P = 0.004). Protein expression of Complex V (P < 0.001) and Complex III (P = 0.002) of the electron transport chain were also reduced in males. Maternal hypothyroidism reduced LZ (PTrt<0.001) and fetal plasma triglycerides (P = 0.019) while fetal free fatty acids and the expression of LZ lipid transporters was not affected.

DISCUSSION

Overall, maternal hypothyroidism may lead to FGR through reduced maternal T4 availability, changes to placental morphology, altered nutrient transporter expression and sex-specific effects on placental metabolism. Changes to LZ glycogen and triglyceride stores as well as mitochondrial content suggest a metabolic shift from oxidative phosphorylation to anaerobic glycolysis in males. These changes also likely impact fetal substrate availability and therefore fetal growth.

Serine Administration Improves Selenium Status, Oxidative Stress, and Mitochondrial Function in Longissimus Dorsi Muscle of Piglets with Intrauterine Growth Retardation

Intrauterine growth retardation (IUGR) causes oxidative stress in the skeletal muscle. Serine and selenoproteins are involved in anti-oxidative processes; however, whether IUGR affects selenium status and whether serine has beneficial effects remain elusive. Here, we investigated the effects of serine administration on selenium nutritional status and oxidative stress in the longissimus dorsi muscle of piglets with IUGR. Six newborn Min piglets having normal birth weight were administered saline, and 12 IUGR piglets were either administered saline or 0.8% serine. The results showed a lower selenium content in skeletal muscle in IUGR piglets, which was restored after serine administration. IUGR piglets showed a disturbed expression of genes encoding selenoproteins, with decreased expression of GPX2, GPX4, TXNRD1, and TXNRD3 and increased expression of DIO1, DIO2, SELF, SELM, SELP, and SELW. Notably, serine administration restored the expression levels of these genes. In accordance with the changes in gene expression, the activity of GPX, TXNRD, and DIO and the content of GSH and SELP were also altered, whereas serine administration restored their contents and activities. Moreover, we observed severe oxidative stress in the skeletal muscle of IUGR piglets, as indicated by decreased GSH content and increased MDA and PC content, whereas serine administration alleviated these changes. In conclusion, our results indicate that IUGR piglets showed a disturbed expression of genes encoding selenoproteins, accompanied by severe oxidative stress. Serine administration can improve selenium status, oxidative stress, and mitochondrial function in the longissimus dorsi muscle of piglets with IUGR. These results suggest that serine could potentially be used in the treatment of IUGR in piglets.

Adverse perinatal conditions and the developmental origins of thyroid dysfunction-Lessons from Animal Models

PURPOSE

Nutritional, hormonal, and environmental status during development can predispose the individual to obesity and endocrine diseases later in life, an association known as metabolic programming. In general, weight loss or gain are seen in thyroid disorders, and thyroid function can be affected by body adiposity. In addition, hyper- and hypothyroidism can be related to metabolic programming. Our aim was to gather evidence that regardless of the type or critical window of metabolic imprinting, offspring exposed to certain adverse perinatal conditions have a higher risk of developing thyroid dysfunction.

METHODS

We reviewed literature data that relate insults occurring during pregnancy and/or lactation to short- and long-term offspring thyroid dysfunction in animal models.

RESULTS

Few studies have addressed the hypothalamic-pituitary-thyroid axis and thyroid dysfunction related to metabolic programming. The literature shows that under- and overnutrition, exposure to endocrine disruptors, early weaning, maternal thyroid disease and maternal high-fat diet can induce alterations in offspring thyroid function in a sex-dependent manner.

CONCLUSION

Based on the few available data, mainly in rodent models, we can conclude that diet, hormones, and environmental contaminants are related to the developmental origins of later thyroid dysfunction by interrupting the normal maturation of the thyroid gland.

Thyroid hormones: Metabolism and transportation in the fetoplacental unit

The thyroid hormones (THs), thyroxine (T4) and triiodothyronine (T3), are of vital importance for fetal development. The concentration of THs in fetal circulation varies throughout gestation and differs from the concentration in the maternal serum, indicating the presence of maternal-fetal thyroid homeostasis regulatory mechanisms in the placenta. The passage of THs from maternal circulation to fetal circulation is modulated by plasma membrane transporters, enzymes, and carrier proteins. Monocarboxylate transporter 8, iodothyronine deiodinases (DIO2 and DIO3), and transthyretin are especially involved in this maternal-fetal thyroid modulation, shown by a greater expression in the placenta. THs also play a role in placental development and as expected, abnormal variations in TH levels are associated with pregnancy complications and can result in damage to the fetus. Although new evidence regarding TH regulation during pregnancy and its effects in the mother, placenta, and fetus has been published, many aspects of these interactions are still poorly understood. The objective of this review is to provide an evidence-based update, drawn from current data, on the metabolism and transport of THs in the placenta and their vital role in the maternal-fetal relationship.

Pregnancy hypothyroidism incidence and complications using the 2011 and 2017 ATA cutoff values. Experience at a maternity hospital in a densely populated area in Mexico City

OBJECTIVES

Normal thyroid activity has an essential role in fetal development, its deficiency may hamper fetal neurodevelopment and neonatal growth. The quantitation of thyroid hormones although useful, still exposes differences on cut off levels to diagnose thyroid deficit accurately that can elicit under or over diagnosis of thyroid dysfuntion.

METHODS

A total of 839 pregnant patients were studied for thyroidal clinical assessment through quantitation of thyroid-stimulating hormone (TSH) and free thyroxine (FT4) circulating levels. Patients evaluated for prenatal and neonatal outcomes. Thyroid function deficiencies were determined with the American Thyroid Association (ATA) 2011 and 2017 values. Statistical analysis searched for associations between variables, odds ratios (OR) and correlations were calculated to evaluate the reliability of the cutoff values recommended by the ATA.

RESULTS

Mean age of our cases was 27.5 + 5.83 years at diagnosis, mean gestational age at first consultation was 23.8 + 10.5 weeks. Mean TSH levels detected were: 2.5 + 1.89 mIU/L, total T3: 3.55 + 4.1 ng/dL, FT4: 3.14 + 4.4 ng/dL. The ATA 2011 values yielded 332 hypothyroidism cases vs. 507 euthyroid patients, a total incidence of 39.6% vs. the ATA 2017 values, diagnosing 100 hypothyroidism cases and 739 euthyroid patients, total incidence of 11.9%. Association with complications were not significant.

CONCLUSIONS

Using ATA 2017 values showed a decreased population with gestational hypothyroidism, hence preventing overdiagnosis and over-treatment. No significant complications were associated, requiring the determination of new regional values. Education and sensibilization of our population is needed to comply with early prenatal consultation and thyroid function testing.

Phthalate Exposures and Placental Health in Animal Models and Humans: A Systematic Review

Phthalates are ubiquitous compounds known to leach from the plastic products that contain them. Due to their endocrine-disrupting properties, a wide range of studies have elucidated their effects on reproduction, metabolism, neurodevelopment, and growth. Additionally, their impacts during pregnancy and on the developing fetus have been extensively studied. Most recently, there has been interest in the impacts of phthalates on the placenta, a transient major endocrine organ critical to maintenance of the uterine environment and fetal development. Phthalate-induced changes in placental structure and function may have significant impacts on the course of pregnancy and ultimately, child health. Prior reviews have described the literature on phthalates and placental health; however to date, there has been no comprehensive, systematic review on this topic. Here, we review 35 papers (24 human and 11 animal studies) and summarize phthalate exposures in relation to an extensive set of placental measures. Phthalate-related alterations were reported for placental morphology, hormone production, vascularization, histopathology, and gene/protein expression. The most consistent changes were observed in vascular and morphologic endpoints, including cell composition. These changes have implications for pregnancy complications such as preterm birth and intrauterine growth restriction as well as potential ramifications for children's health. This comprehensive review of the literature, including common sources of bias, will inform the future work in this rapidly expanding field.

Maternal Hypothyroidism in Rats Reduces Placental Lactogen, Lowers Insulin Levels, and Causes Glucose Intolerance

Hypothyroidism increases the incidence of gestational diabetes mellitus (GDM) but the mechanisms responsible are unknown. This study aimed to assess the pathophysiological mechanisms by which hypothyroidism leads to glucose intolerance in pregnancy. Hypothyroidism was induced in female Sprague-Dawley rats by adding methimazole (MMI) to drinking water at moderate (MOD, MMI at 0.005% w/v) and severe (SEV, MMI at 0.02% w/v) doses from 1 week before pregnancy and throughout gestation. A nonpregnant cohort received the same dose for the same duration but were not mated. On gestational day 16 (GD16), or nonpregnant day 16 (NP16), animals were subjected to an intraperitoneal glucose tolerance test. Tissues and blood samples were collected 4 days later. Hypothyroidism induced a diabetic-like phenotype by GD16 in pregnant females only. Pregnant MOD and SEV females had reduced fasting plasma insulin, less insulin following a glucose load, and altered expression of genes involved in insulin signaling within skeletal muscle and adipose tissue. Hypothyroidism reduced rat placental lactogen concentrations, which was accompanied by reduced percentage β-cell cross-sectional area (CSA) relative to total pancreas CSA, and a reduced number of large β-cell clusters in the SEV hypothyroid group. Plasma triglycerides and free fatty acids were reduced by hypothyroidism in pregnant rats, as was the expression of genes that regulate lipid homeostasis. Hypothyroidism in pregnant rats results in a diabetic-like phenotype that is likely mediated by impaired β-cell expansion in pregnancy. This pregnancy-specific phenomenon is likely due to reduced placental lactogen secretion.

Gaps in the knowledge of thyroid hormones and placental biology

Thyroid hormones (THs) are required for the growth and development of the foetus, stimulating anabolism and oxygen consumption from the early stages of pregnancy to the period of foetal differentiation close to delivery. Maternal changes in the hypothalamic–pituitary thyroid axis are also well known. In contrast, several open questions remain regarding the relationships between the placenta and the maternal and foetal TH systems. The exact mechanism by which the placenta participates in regulating the TH concentration in the foetus and mother and the role of TH in the placenta are still poorly studied. In this review, we aim to summarize the available data in the area and highlight significant gaps in our understanding of the ontogeny and cell-specific localization of TH transporters, TH receptors and TH metabolic enzymes in the placenta in both human and rodent models. Significant deficiencies also exist in knowledge of the contribution of genomic and nongenomic effects of TH on the placenta and finally how the placenta reacts during pregnancy when the mother has thyroid disease. By addressing these key knowledge gaps, improved pregnancy outcomes and management of women with thyroid alterations may be possible.

Prevalence of Subclinical Hypothyroidism in Pregnancy and Its Association With Anti-thyroperoxidase Antibody and the Occurrence of Gestational Diabetes Mellitus

Introduction

Subclinical hypothyroidism (SCH) and gestational diabetes mellitus (GDM) are common endocrinological abnormalities associated with pregnancy. The presence of a raised anti-thyroperoxidase (anti-TPO) antibody titer increases the risk of progression of subclinical hypothyroidism to overt hypothyroidism. Subclinical hypothyroidism and GDM are known to affect maternal and fetal outcomes adversely. A few studies have shown an increased risk of GDM with autoimmune hypothyroidism. However, data regarding this association between GDM, SCH, and anti-TPO Ab are scarce. This study aimed to find the prevalence of autoimmune subclinical hypothyroidism and its association with GDM in pregnancy.

Materials and methods

In a cross-sectional study, 382 pregnant women at their first antenatal checkup (ANC) were enrolled in the study. Serum thyroid-stimulating hormone (TSH), free T4 (FT4), anti-TPO Ab, and the 75 g oral glucose tolerance test (OGTT) were evaluated. The results obtained were analyzed in Systat Version 13.2 (SPSS Inc., Chicago, IL).

Observations

Results showed an SCH prevalence of 37.69% with a raised anti-TPO Ab titer in 49.31% of the diagnosed SCH cases, pointing towards an autoimmune etiology. Our study revealed a GDM prevalence of 12.04%. Out of the 46 GDM cases, 16 were found to have SCH and 3 cases had raised anti-TPO Ab titers. In our study, 27.73% of euthyroid pregnant women had a raised anti-TPO Ab titer. Our study revealed no significant association between GDM, SCH, and raised anti-TPO Ab titer.

Conclusion

Anti-TPO antibody subsequently leads to hypothyroxinemia, for which it is necessary that cases with high titer of anti-TPO antibody though euthyroid should be meticulously followed up and screened for to detect development of hypothyroidism or SCH, particularly in future pregnancies. However, GDM prevalence was at par with the national figure, but with no significant association of SCH and a high anti-TPO ab titer was found with GDM in our study. Further studies with a larger cohort may establish a causal association between the two most common endocrinological disorders observed in pregnancy.

Maternal nutrient restriction alters thyroid hormone dynamics in placentae of sheep having small for gestational age fetuses

Thyroid hormones regulate a multitude of metabolic and cellular processes involved in placental and fetal growth, while maternal nutrient restriction (NR) has the potential to influence these processes. Those fetuses most impacted by NR, as categorized by weight, are termed small for gestational age (SGA), but the role of thyroid hormones in these pregnancies is not fully understood. Therefore, the aims of the present study were to determine effects of NR during pregnancy on maternal and fetal thyroid hormone concentrations, as well as temporal and cell-specific expression of mRNAs and proteins for placental thyroid hormone transporters, thyroid hormone receptors, and deiodinases in ewes having either SGA or normal weight fetuses. Ewes with singleton pregnancies were fed either a 100% NRC (n = 8) or 50% NRC (NR; n = 28) diet from Days 35 to 135 of pregnancy with a single placentome surgically collected on Day 70. Fetal weight at necropsy on Day 135 was used to designate the fetuses as NR NonSGA (n = 7; heaviest NR fetuses) or NR SGA (n = 7; lightest NR fetuses). Thyroid hormone levels were lower in NR SGA compared to NR NonSGA ewes, while all NR fetuses had lower concentrations of thyroxine at Day 135. Expression of mRNAs for thyroid hormone transporters SLC16A2, SLC16A10, SLCO1C1, and SLCO4A1 were altered by day, but not nutrient restriction. Expression of THRA mRNA and protein was dysregulated in NR SGA fetuses with protein localized to syncytial and stromal cells in placentomes in all groups. The ratio of deiodinases DIO2 and DIO3 was greater for NR SGA placentae at Day 70, while DIO3 protein was less abundant in placentae from NR SGA than 100% NRC ewes. These results identify mid-gestational modifications in thyroid hormone-associated proteins in placentomes of ewes having SGA fetuses, as well as a potential for placentomes from NonSGA pregnancies to adapt to, and overcome, nutritional restrictions during pregnancy.

Effects of isolated maternal hypothyroxinemia on adverse pregnancy outcomes

PURPOSE

There are conflicting results about the effects of maternal hypothyroidism (IMH) on adverse pregnancy outcomes. This study aimed to investigate the relationship between IMH identified in the first trimester of gestation and adverse pregnancy outcomes.

METHODS

In this prospective cohort study, we used data from the Tehran Thyroid and Pregnancy study (TTPs). To diagnose IMH, we considered a threshold of 2.04 for FTI, which was based on the 10th percentile of this marker identified in the 1st trimesters. A generalized linear regression (GLM) model adjusted for the gravidity, urine iodine, and TPOAb status was applied to assess the effects of IMH on adverse pregnancy outcomes, compared to the controls group.

RESULTS

Penalized logistic regression analysis indicated that the adjusted odds ratio (aOR) of Preterm premature rupture of the membranes (PPROM) in women with IMH was 5.43-folder higher than euthyroid group [aOR 5.43, 95% CI (1.40, 21.1), p = 0.01]. Besides, the adjusted odds ratio of low birth weight (LBW) in the IMH group was 2.53-folder higher than the healthy group [aOR 2.53, 95% CI (1.01, 6.33), p = 0.047]. Furthermore, the results of the GLM adjusted model revealed that the mean of neonatal head circumference and weight in the IMH group was around 0.43 cm (95% CI - 0.80, - 0.07, p = 0.02) and 145.4 g (95% CI - 242.6, - 48.1, p = 0.003) lower than euthyroid group, respectively.

CONCLUSIONS

This study demonstrated that women with IMH identified in early pregnancy have a higher odds ratio for developing some adverse pregnancy outcomes, including PPROM and LBW compared to their euthyroid counterparts. Also, the neonatal head circumference and weight in the IMH group were lower than in the euthyroid group.

The interplay between thyroid hormones and the placenta: a comprehensive review†

Thyroid hormones (THs) regulate a number of metabolic processes during pregnancy. After implantation, the placenta forms and enhances embryonic growth and development. Dysregulated maternal THs signaling has been observed in malplacentation-mediated pregnancy complications such as preeclampsia, miscarriage, and intrauterine growth restriction (IUGR), but the molecular mechanisms involved in this association have not been fully characterized. In this review, we have discussed THs signaling and its roles in trophoblast proliferation, trophoblast differentiation, trophoblast invasion of the decidua, and decidual angiogenesis. We have also explored the relationship between specific pregnancy complications and placental THs transporters, deiodinases, and THs receptors. In addition, we have examined the effects of specific endocrine disruptors on placental THs signaling. The available evidence indicates that THs signaling is involved in the formation and functioning of the placenta and serves as the basis for understanding the pathogenesis and pathophysiology of dysthyroidism-associated pregnancy complications such as preeclampsia, miscarriage, and IUGR.

Role of thyroid hormones in normal and abnormal central nervous system myelination in humans and rodents

Thyroid hormones (THs) are instrumental in promoting the molecular mechanisms which underlie the complex nature of neural development and function within the central nervous system (CNS) in vertebrates. The key neurodevelopmental process of myelination is conserved between humans and rodents, of which both experience peak fetal TH concentrations concomitant with onset of myelination. The importance of supplying adequate levels of THs to the myelin producing cells, the oligodendrocytes, for promoting their maturation is crucial for proper neural function. In this review we examine the key TH distributor and transport proteins, including transthyretin (TTR) and monocarboxylate transporter 8 (MCT8), essential for supporting proper oligodendrocyte and myelin health; and discuss disorders with impaired TH signalling in relation to abnormal CNS myelination in humans and rodents. Furthermore, we explore the importance of using novel TH analogues in the treatment of myelination disorders associated with abnormal TH signalling.

Associations of Hypothyroxinemia With Risk of Preeclampsia-Eclampsia and Gestational Hypertension

OBJECTIVE

To investigate the association between hypothyroxinemia and the risk of preeclampsia-eclampsia and gestational hypertension.

DESIGN

Historical cohort study.

METHODS

The study included pregnant individuals who delivered live-born singletons and had at least one thyroid function assessment during pregnancy at a tertiary hospital. Hypothyroxinemia was defined as thyroid-stimulating hormone (TSH) levels within the normal reference range and free thyroxine (FT4) levels lower than the tenth percentile. Risk ratios (RRs) with 95% confidence intervals (95% CIs) for preeclampsia-eclampsia and gestational hypertension between women with and without a diagnosis of hypothyroxinemia during pregnancy were estimated using a generalized estimating equation model.

RESULTS

A total of 59,463 women with live-born singletons were included in the analysis. Logistic regression models with restricted cubic spline suggested that there was a U-shaped association between FT4 levels and preeclampsia-eclampsia risk. Compared with euthyroid women, those with hypothyroxinemia had an increased risk of preeclampsia-eclampsia (RR = 1.16, 95% CI: 1.02-1.31), and the risk increased with the increasing severity of hypothyroxinemia (p for trend < 0.001). Moreover, persistent hypothyroxinemia from the first to second trimesters was associated with an increased risk of preeclampsia-eclampsia (RR = 1.37, 95% CI: 1.03-1.83), especially for women with severe hypothyroxinemia (RR = 1.70, 95% CI: 1.12-2.58). In contrast, there was no association between hypothyroxinemia and gestational hypertension.

CONCLUSION

Our study suggested that hypothyroxinemia was only associated with an increased risk of preeclampsia-eclampsia, especially in women with persistent hypothyroxinemia in the first half of pregnancy. Analyses of the associated risk of gestational hypertension with hypothyroxinemia were not significant.

Long term outcomes of infants born by mothers with thyroid dysfunction during pregnancy

According to Barker’s hypothesis, sub-optimal conditions during gestation might affect the predisposition for diseases in adulthood. Alteration in endocrine functions during pregnancy, such us thyroid function or glucose metabolism, are not exempt. It is well known that subclinical hypothyroidism and thyroperoxidase antibodies-positive euthyroidism during early pregnancy are associated with increased risk of gestational diabetes mellitus and both conditions influence pregnancy outcome and newborn development and metabolism at short and long terms. Fetal production of thyroid hormones starts from the 12th week of gestational age. The transplacental passage of maternal thyroxine (T4) is therefore essential for the fetal neurological development, especially during the first half of pregnancy. If this passage is interrupted, such as in premature birth, neonates are more susceptible to develop impaired thyroid function, because of physiological immaturity of their hypothalamic-pituitary-thyroid axis, acute illnesses and stressful events (sepsis, invasive procedures, drugs). The aim of this review is to investigate the short and long term effects of maternal dysthyroidisms on term and preterm newborns, with particular attention to the metabolic and thyroid consequences. Metabolic syndrome, higher body mass index and greater waist circumference, seem to be more prevalent in children of TPO-Ab-positive mothers. Maternal hypothyroidism may be associated with higher risk of gestational diabetes and adverse birth outcomes, such as preeclampsia, preterm delivery, fetal death and low birth weight offspring. In adulthood, preterm (< 37 weeks of gestational age) or low birth weight (<2.500 g) newborns seem to be more susceptible to develop gestational diabetes, preeclampsia, type 2 diabetes mellitus and behavioral alterations. (www.actabiomedica.it)

Identification of Pathways Associated with Placental Adaptation to Maternal Nutrient Restriction in Sheep

Maternal nutrient restriction impairs placental growth and development, but available evidence suggests that adaptive mechanisms exist, in a subset of nutrient restricted (NR) ewes, that support normal fetal growth and do not result in intrauterine growth restriction (IUGR). This study utilized Affymetrix GeneChip Bovine and Ovine Genome 1.0 ST Arrays to identify novel placental genes associated with differential fetal growth rates within NR ewes. Singleton pregnancies were generated by embryo transfer and, beginning on Day 35 of pregnancy, ewes received either a 100% National Research Council (NRC) (control-fed group; n = 7) or 50% NRC (NR group; n = 24) diet until necropsy on Day 125. Fetuses from NR ewes were separated into NR non-IUGR (n = 6) and NR IUGR (n = 6) groups based on Day 125 fetal weight for microarray analysis. Of the 103 differentially expressed genes identified, 15 were upregulated and 88 were downregulated in NR non-IUGR compared to IUGR placentomes. Bioinformatics analysis revealed that upregulated gene clusters in NR non-IUGR placentomes associated with cell membranes, receptors, and signaling. Downregulated gene clusters associated with immune response, nutrient transport, and metabolism. Results illustrate that placentomal gene expression in late gestation is indicative of an altered placental immune response, which is associated with enhanced fetal growth, in a subpopulation of NR ewes.

Intrauterine growth restriction alters growth performance, plasma hormones, and small intestinal microbial communities in growing-finishing pigs

Background

The interaction of the gut microbiota with key metabolic and physiological processes may be associated with poor growth outcomes in animals born with intrauterine growth restriction (IUGR).

Results

Growth performance, plasma hormone concentrations, and intestinal microbiota composition were analyzed in IUGR pigs and in normal birth weight (NBW) pigs when the NBW pigs reached 25, 50, and 100 kg of body weight (BW). Compared to NBW pigs, IUGR pigs had lower initial, weaned, and final BW, and lower average daily gain and average daily feed intake in all the considered time points. In the 25 kg BW group, IUGR pigs had higher concentrations of plasma ghrelin and pancreatic polypeptide (PP), but lower insulin concentration than NBW pigs, while the situation was reversed in the 50 kg BW group. As compared to NBW pigs, IUGR pigs had higher microbial alpha diversity in the jejunum and ileum; in the 50 and 100 kg BW groups, IUGR pigs had higher Firmicutes abundance but lower Proteobacteria abundance in the jejunum, and lower Lactobacillus abundance in the jejunum and ileum; in the 25 kg BW group, IUGR pigs showed higher unclassified Ruminococcaceae abundance in the ileum; and in 25 and 50 kg BW groups, IUGR pigs showed lower Ochrobactrum abundance in the jejunum. Spearman’s correlation revealed that Lactobacillus was negatively correlated with growth performance, while unclassified Ruminococcaceae was positively correlated. Predictive metagenomic analysis detected significantly different expression of genes in the intestinal microbiota between IUGR and NBW pigs, suggesting different metabolic capabilities between the two groups.

Conclusions

Growing-finishing IUGR pigs showed lower growth performance, higher microbial alpha diversity, and differences in plasma hormone concentrations compared to NBW pigs. Alterations in the abundance of Firmicutes, Proteobacteria, Ruminococcaceae, Lactobacillus, and Ochrobactrum in the small intestine may be associated with IUGR, and may therefore serve as a future target for gut microbiota intervention in growing-finishing IUGR pigs.

Cell Type- and Sex-Specific Dysregulation of Thyroid Hormone Receptors in Placentas in Gestational Diabetes Mellitus

Thyroid hormones are essential for development of trophoblasts and the fetus. They also regulate a wide range of metabolic processes. We investigated the influence of maternal gestational diabetes mellitus (GDM) on thyroid hormone receptor (THR) isoforms THRα1, THRα2, THRβ1 and THRβ2 of the human placenta in a sex- and cell-type specific manner. Term placental tissue was obtained from women with (n = 40) or without GDM (control; n = 40). THRs levels were measured by semi-quantitative immunohistochemistry and real-time qRT-PCR. We localized THR immunostaining in syncytiotrophoblast (SCT), which was the tissue with the strongest signal. Double immunofluorescence identified THR in decidual cells in the stroma and in extravillous cytotrophoblasts. GDM did not change THRα1 immunolabelling intensity in decidua, but was associated with a stronger immunolabelling in SCT compared to GDM (p < 0.05). The SCT difference of GDM vs. control was strongest (p < 0.01) in female placentas. THRα2 was only weakly present and immunolabelling was weaker (p < 0.05) in SCT of only male GDM placentas in comparison to male controls. THRβ1/β2 immunostaining was weak in all cell types without changes in GDM. However, more THRβ1/2 protein was present (p < 0.001) in male than female placentas. All these protein changes were paralleled by changes of THR transcript levels. The data show that THR are expressed in term trophoblast in relation to fetal sex. Maternal GDM influences predominantly THRα1 in SCT, with the strongest GDM effect in SCT of female placentas.

PBDEs Concentrate in the Fetal Portion of the Placenta: Implications for Thyroid Hormone Dysregulation

During pregnancy, the supply of thyroid hormone (TH) to the fetus is critically important for fetal growth, neural development, metabolism, and maintenance of pregnancy. Additionally, in cases where maternal and placental TH regulation is significantly altered, there is an increased risk of several adverse pregnancy outcomes. It is unclear what may be disrupting placental TH regulation; however, studies suggest that environmental contaminants, such as polybrominated diphenyl ethers (PBDEs), could be playing a role. In this study, Wistar rats were gestationally exposed to a mixture of PBDEs for 10 days. THs and PBDEs were quantified in paired maternal serum, dissected placenta, and fetuses, and mRNA expression of transporters in the placenta was assessed. Significantly higher concentrations of PBDEs were observed in the fetal portion of the placenta compared with the maternal side, suggesting that PBDEs are actively transported across the interface. PBDEs were also quantified in 10 recently collected human maternal and fetal placental tissues; trends paralleled observations in the rat model. We also observed an effect of PBDEs on T3 levels in dam serum, as well as suggestive changes in the T3 levels of the placenta and fetus that varied by fetal sex. mRNA expression in the placenta also significantly varied by fetal sex and dose. These observations suggest the placenta is a significant modifier of fetal exposures, and that PBDEs are impacting TH regulation in a sex-specific manner during this critical window of development.

Thyroid hormones and female reproduction

Thyroid hormones are vital for the proper functioning of the female reproductive system, since they modulate the metabolism and development of ovarian, uterine, and placental tissues. Therefore, hypo- and hyperthyroidism may result in subfertility or infertility in both women and animals. Other well-documented sequelae of maternal thyroid dysfunctions include menstrual/estral irregularity, anovulation, abortion, preterm delivery, preeclampsia, intrauterine growth restriction, postpartum thyroiditis, and mental retardation in children. Several studies have been carried out involving prospective and retrospective studies of women with thyroid dysfunction, as well as in vivo and in vitro assays of hypo- and hyperthyroidism using experimental animal models and/or ovarian, uterine, and placental cell culture. These studies have sought to elucidate the mechanisms by which thyroid hormones influence reproduction to better understand the physiology of the reproductive system and to provide better therapeutic tools for reproductive dysfunctions that originate from thyroid dysfunctions. Therefore, this review aims to summarize and update the available information related to the role of thyroid hormones in the morphophysiology of the ovary, uterus, and placenta in women and animals and the effects of hypo- and hyperthyroidism on the female reproductive system.

Thyroid Function in Monozygotic Twins with Intra-twin Birth Weight Differences: A Prospective Longitudinal Cohort Study

OBJECTIVE

To analyze the long-term impact of birth weight (BW) on thyroid function in genetically identical twins with intra-twin BW differences from birth to adolescence.

STUDY DESIGN

In total, 52 monozygotic twin pairs underwent at least one analysis of thyroid function at mean ages of 10.1 years (27 pairs), 15.1 years (35 pairs), and 17.4 years (36 pairs); 18 pairs donated blood at all time points. BW difference of <1 SDS was defined as concordant, BW difference ≥1 SDS as discordant.

RESULTS

In concordant twins, no significant differences were observed. In the discordant group, smaller twins had higher mean thyroid-stimulating hormone (TSH) than their larger co-twins at 10.1 years (3.6 vs 2.5 μU/mL; P = .04) and 15.1 years (2.6 vs 2.2 μU/mL; P = .08). Smaller twins showed lower mean thyroxine than larger co-twins at 10.1 years (7.8 vs 8.2 μg/dL P = .05) and 17.4 years (7.7 vs 8.4 μg/dL; P = .03), and a tendency at 15.1 years (6.9 vs 7.4 μg/dL; P = .09). Calculation of TSH-thyroxine ratio revealed significant differences in the discordant group, with greater ratios in the smaller twin at 10.1 years (0.5 vs 0.3; P = .006) and 15.1 years (0.4 vs 0.3; P = .04).

CONCLUSIONS

In this group of monozygotic twins with intra-twin BW differences, BW seemed to exert a long-lasting impact on thyroid function. This may be due to a delay in hypothalamic-pituitary-thyroid axis maturation, with TSH resistance during childhood and early adolescence in children with low BW.

The placenta in fetal thyroid hormone delivery: from normal physiology to adaptive mechanisms in complicated pregnancies

Context: Thyroid hormones are indispensable for normal fetal development. Since the fetus depends to a large extent on maternal thyroid hormone supply through the placenta, this challenges maternal thyroid economy. Several molecular mechanisms are involved in placental thyroid hormone transport and metabolism. Chronic pregnancy complications, associated with utero-placental hypoxia, trigger the development of accelerated placental maturation in order to improve fetal-placental exchange to strengthen the offspring's chance of survival. This review provides an overview of normal maternal-fetal thyroid hormone supply and explores the presence of placental adaptive mechanisms in complicated pregnancies with chronical utero-placental hypoxia to improve the thyroid hormone supply to the fetus under pressure, to end with reflections about the long term health consequences.Evidence acquisition: This work is based on a comprehensive literature review of the PubMed and Embase database, including relevant articles from 1969 to June 2018.Conclusions: The placenta is actively involved in fetal thyroid hormone delivery through a combination of stimulatory and inhibitory mechanisms. Parallel with histological adaptations to improve transplacental fetal-maternal exchange, there are indications of placental adaptive mechanisms in thyroid hormone transport and metabolism in case of complicated pregnancies, from animal models and in-vitro experiments. Evidence from human in-vivo studies is limited due to heterogeneity in study populations, small study samples, and technical limitations. Further research is necessary to reveal the role of the placenta in pathological circumstances. The placenta might thus be considered as the infants' black box of pregnancy. Results will contribute to more insights in the concept of fetal programming, which lays the foundations of optimum health, growth, and neurodevelopment across the lifespan.

Children Born Small for Gestational Age: Differential Diagnosis, Molecular Genetic Evaluation, and Implications

Children born small for gestational age (SGA), defined as a birth weight and/or length below -2 SD score (SDS), comprise a heterogeneous group. The causes of SGA are multifactorial and include maternal lifestyle and obstetric factors, placental dysfunction, and numerous fetal (epi)genetic abnormalities. Short-term consequences of SGA include increased risks of hypothermia, polycythemia, and hypoglycemia. Although most SGA infants show catch-up growth by 2 years of age, ∼10% remain short. Short children born SGA are amenable to GH treatment, which increases their adult height by on average 1.25 SD. Add-on treatment with a gonadotropin-releasing hormone agonist may be considered in early pubertal children with an expected adult height below -2.5 SDS. A small birth size increases the risk of later neurodevelopmental problems and cardiometabolic diseases. GH treatment does not pose an additional risk.

Dopamine synthesis and dopamine receptor expression are disturbed in recurrent miscarriages

OBJECTIVES

l-dopa decarboxylase (DDC) is responsible for the synthesis of dopamine. Dopamine, which binds to the D₂-dopamine receptor (D2R), plays an important role in the maintenance of pregnancy. Aim of our study was the analysis of DDC and D2R expression in placentas of spontaneous miscarriages (SMs) and recurrent miscarriages (RMs) in comparison to healthy controls.

METHODS

Patients with SM (n = 15) and RM (n = 15) were compared with patients from healthy pregnancies (n = 15) (pregnancy weeks 7-13 each). Placental tissue has been collected from SMs and RMs from the first trimester (Department of Gynaecology and Obstetrics, LMU Munich) and from abruptions (private practice, Munich). Placental cell lines, BeWo- and JEG-3 cells, were stimulated with the trace amines T₀AM and T₁AM in vitro.

RESULTS

Levels of DDC and D2R in trophoblasts and the decidua were lower in RMs in comparison to healthy controls. Stimulation of BeWo cells with T₁AM significantly reduced DDC mRNA and protein levels. Via double-immunofluorescence, a DDC-positive cell type beneath decidual stromal cells and foetal EVT in the decidua could be detected.

CONCLUSIONS

Downregulation of DDC and D2R in trophoblasts of RMs reflects a reduced signal cascade of catecholamines on the foetal side.

Thyroid hormone regulates protease expression and activation of Notch signaling in implantation and embryo development

A clinical association between thyroid dysfunction and pregnancy complications has been extensively reported; however, the molecular mechanisms through which TH might regulate key events of pregnancy have not been elucidated yet. In this respect, we performed in vivo studies in MMI-induced hypothyroid pregnant mice, evaluating the effect of hypothyroidism on the number of implantation sites, developing embryos/resorptions and pups per litter, at 4.5, 10.5, 18.5 days post-coitum (dpc) and at birth. We also studied the expression of major molecules involved in implantation and placentation, such as the proteases ISPs, MMPs, TIMPs and Notch pathway-related genes. Our results demonstrate that hypothyroidism may have a dual effect on pregnancy, by initially influencing implantation and by regulating placental development at later stages of gestation. To further elucidate the role of TH in implantation, we performed in vitro studies by culturing 3.5 dpc blastocysts in the presence of TH, with or without endometrial cells used as the feeder layer, and studied their ability to undergo hatching and outgrowth. We observed that, in the presence of endometrial feeder cells, TH is able to anticipate blastocyst hatching by upregulating the expression of blastocyst-produced ISPs, and to enhance blastocyst outgrowth by upregulating endometrial ISPs and MMPs. These results clearly indicate that TH is involved in the bidirectional crosstalk between the competent blastocyst and the receptive endometrium at the time of implantation.

Blocked, delayed, or obstructed: What causes poor white matter development in intrauterine growth restricted infants?

Poor white matter development in intrauterine growth restricted (IUGR) babies remains a major, untreated problem in neonatology. New therapies, guided by an understanding of the mechanisms that underlie normal and abnormal oligodendrocyte development and myelin formation, are required. Much of our knowledge of the mechanisms that underlie impaired myelination come from studies in adult demyelinating disease, preterm brain injury, or experimental models of hypoxia-ischemia. However, relatively less is known for IUGR which is surprising because IUGR is a leading cause of perinatal mortality and morbidity, second only to premature birth. IUGR is also a significant risk factor for the later development of cerebral palsy, and is a greater risk compared to some of the more traditionally researched antecedents - asphyxia and inflammation. Recent evidence suggests that the white matter injury and reduced myelination in the brains of some preterm babies is due to impaired maturation of oligodendrocytes thereby resulting in the reduced capacity to synthesize myelin. Therefore, it is not surprising that the hypomyelination observable in the central nervous system of IUGR infants has similarly lead to investigations identifying a delay or blockade in the progress of maturation of oligodendrocytes in these infants. This review will discuss current ideas thought to account for the poor myelination often present in the neonate's brain following IUGR, and discuss novel interventions that are promising as treatments that promote oligodendrocyte maturation, and thereby repair the myelination deficits that otherwise persist into infancy and childhood and lead to neurodevelopmental abnormalities.

Hypothyroidism in utero stimulates pancreatic beta cell proliferation and hyperinsulinaemia in the ovine fetus during late gestation

Key points

Thyroid hormones are important regulators of growth and maturation before birth, although the extent to which their actions are mediated by insulin and the development of pancreatic beta cell mass is unknown.

Hypothyroidism in fetal sheep induced by removal of the thyroid gland caused asymmetric organ growth, increased pancreatic beta cell mass and proliferation, and was associated with increased circulating concentrations of insulin and leptin.

In isolated fetal sheep islets studied in vitro, thyroid hormones inhibited beta cell proliferation in a dose‐dependent manner, while high concentrations of insulin and leptin stimulated proliferation.

The developing pancreatic beta cell is therefore sensitive to thyroid hormone, insulin and leptin before birth, with possible consequences for pancreatic function in fetal and later life.

The findings of this study highlight the importance of thyroid hormones during pregnancy for normal development of the fetal pancreas.

Abstract

Development of pancreatic beta cell mass before birth is essential for normal growth of the fetus and for long‐term control of carbohydrate metabolism in postnatal life. Thyroid hormones are also important regulators of fetal growth, and the present study tested the hypotheses that thyroid hormones promote beta cell proliferation in the fetal ovine pancreatic islets, and that growth retardation in hypothyroid fetal sheep is associated with reductions in pancreatic beta cell mass and circulating insulin concentration in utero. Organ growth and pancreatic islet cell proliferation and mass were examined in sheep fetuses following removal of the thyroid gland in utero. The effects of triiodothyronine (T₃), insulin and leptin on beta cell proliferation rates were determined in isolated fetal ovine pancreatic islets in vitro. Hypothyroidism in the sheep fetus resulted in an asymmetric pattern of organ growth, pancreatic beta cell hyperplasia, and elevated plasma insulin and leptin concentrations. In pancreatic islets isolated from intact fetal sheep, beta cell proliferation in vitro was reduced by T₃ in a dose‐dependent manner and increased by insulin at high concentrations only. Leptin induced a bimodal response whereby beta cell proliferation was suppressed at the lowest, and increased at the highest, concentrations. Therefore, proliferation of beta cells isolated from the ovine fetal pancreas is sensitive to physiological concentrations of T₃, insulin and leptin. Alterations in these hormones may be responsible for the increased beta cell proliferation and mass observed in the hypothyroid sheep fetus and may have consequences for pancreatic function in later life.

Thyroid hormones are important regulators of growth and maturation before birth, although the extent to which their actions are mediated by insulin and the development of pancreatic beta cell mass is unknown.

Hypothyroidism in fetal sheep induced by removal of the thyroid gland caused asymmetric organ growth, increased pancreatic beta cell mass and proliferation, and was associated with increased circulating concentrations of insulin and leptin.

In isolated fetal sheep islets studied in vitro, thyroid hormones inhibited beta cell proliferation in a dose‐dependent manner, while high concentrations of insulin and leptin stimulated proliferation.

The developing pancreatic beta cell is therefore sensitive to thyroid hormone, insulin and leptin before birth, with possible consequences for pancreatic function in fetal and later life.

The findings of this study highlight the importance of thyroid hormones during pregnancy for normal development of the fetal pancreas.

Environmental chemicals and preterm birth: Biological mechanisms and the state of the science

PURPOSE OF REVIEW

Preterm birth is a significant worldwide health problem of uncertain origins. The extant body of literature examining environmental contaminant exposures in relation to preterm birth is extensive but results remain ambiguous for most organic pollutants, metals and metalloids, and air pollutants. In the present review we examine recent epidemiologic studies investigating these associations, and identify recent advances and the state of the science. Additionally, we highlight biological mechanisms of action in the pathway between chemical exposures and preterm birth, including inflammation, oxidative stress, and endocrine disruption, that deserve more attention in this context.

RECENT FINDINGS

Important advances have been made in the study of the environment and preterm birth, particularly in regard to exposure assessment methods, exploration of effect modification by co-morbidities and exposures, and in identification of windows of vulnerability during gestation. There is strong evidence for an association between maternal exposure to some persistent pesticides, lead, and fine particulate matter, but data on other contaminants is sparse and only suggestive trends can be noted with the current data.

SUMMARY

Beyond replicating current findings, further work must be done to improve understanding of mechanisms underlying the associations observed between environmental chemical exposures and preterm birth. By examining windows of vulnerability, disaggregating preterm birth by phenotypes, and measuring biomarkers of mechanistic pathways in these epidemiologic studies we can improve our ability to detect associations with exposure, provide additional evidence for causality in an observational setting, and identify opportunities for intervention.

Development of the independent function of fetal thyroid glands in the dog in connection with iodothyronine concentrations in pregnant bitches, fetal fluids, and fetal serum

Thyroxine (T₄) and triiodothyronine (T₃) concentrations in pregnant and nonpregnant bitches were measured. The allantoic and amniotic fluid samples were collected separately in the third week of pregnancy, and fetal blood samples were collected in the fourth week of pregnancy. There was no difference between T₄ results in the pregnant and nonpregnant animals, but the measured serum concentrations exceeded the healthy range for normal adults. Serum T₄ concentrations were lower in the fetus than those in adults (P < 0.01). Fetal T₄ concentrations continuously increased and reached 13.38 ± 6.19 nmol/L before birth. The fetal serum T₄ concentrations were lower than the T₄ concentrations in allantoic and amniotic fluid until the seventh week, and the fetal serum T₃ concentrations were lower than those in fetal fluids throughout the pregnancy (P < 0.01). Maximum T₃ concentrations in allantoic and amniotic fluid exceeded the concentrations in the fetal and maternal serum. It is conceivable that the considerable differences between maternal and fetal serum T₄ concentrations in healthy animals are explained by the T₄ impermeability of the placenta. Extremely high maternal T₄ (193.5 nmol/L) in 1 bitch was associated with T₄ concentrations under the detection limit in the fetal fluids and serum suggesting an inhibitory effect. The T₄ concentrations in all the fetal fluids and serum were under the detectable concentration that can be defined by 3.0 nmol/L in that bitch. We have demonstrated that fetal thyroid glands start functioning independently at the same time as thyroid cell formation in the dog, but the overproduction of maternal T₄ may have a suppressive effect on fetal iodothyronine production.

The Risk of Preeclampsia According to High Thyroid Function in Pregnancy Differs by hCG Concentration

CONTEXT

During pregnancy, there is an increased demand for thyroid hormone. The pregnancy hormone human chorionic gonadotropin (hCG) is an important physiological stimulator of thyroid function. Already high-normal maternal free T₄ concentrations are associated with a higher risk of preeclampsia.

OBJECTIVE

The objective of the investigation was to study our hypothesis that hCG concentrations can distinguish a physiological form of high thyroid function from a more pathological form of high thyroid function and that the risk of preeclampsia would differ accordingly.

DESIGN

TSH, free T₄, hCG, or thyroperoxidase antibody concentrations were determined in pregnant women participating in a population-based prospective cohort study.

SETTING

The study was conducted in the general community.

PARTICIPANTS

A nonselected sample of 5146 pregnant women participated in the study.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE(S)

Preeclampsia was measured.

RESULTS

Women with high hCG-associated high thyroid function did not have a higher risk of preeclampsia than women with normal thyroid function. In contrast, women with low hCG and high thyroid function had a 3.4- to 11.1-fold higher risk of preeclampsia. These risk estimates were amplified in women with a high body mass index. Women with a low hCG and suppressed TSH (<0.10 mU/L) had a 3.2- to 8.9-fold higher risk of preeclampsia. hCG was not associated with preeclampsia, and results remained similar after exclusion of thyroperoxidase antibody-positive women.

CONCLUSION

This study suggests that, in contrast to women with a high hCG associated high thyroid function, women with low hCG and high thyroid function during pregnancy are at a higher risk of developing preeclampsia. The additional measurement of hCG may therefore help to distinguish a more pathological form of high thyroid function and women at a high risk of preeclampsia.

The expression of thyroid hormone receptors (THR) is regulated by the progesterone receptor system in first trimester placental tissue and in BeWo cells in vitro

BACKGROUND

Thyroid hormones are essential for the maintenance of pregnancy and a deficiency in maternal thyroid hormones has been associated with early pregnancy losses. The aim of this study was a systematic investigation of the influence of mifepristone (RU 486) on the expression of the thyroid hormone receptor (THR) isoforms THRα1, THRα2, THRβ1 and THRβ2 on protein and mRNA-level.

METHODS

Samples of placental tissue were obtained from patients with mifepristone induced termination of pregnancy (n=13) or mechanical induced termination of normal pregnancy (n=20), each from the 4th to 13th week of pregnancy. Expression of THRα1, THRα2, THRβ1 and THRβ2 was analysed on protein level by immunohistochemistry and on mRNA level by real time RT-PCR (TaqMan). The influence of progesterone on THR gene expression was analysed in the trophoblast tumour cell line BeWo by real time RT-PCR (TaqMan).

RESULTS

Nuclear expression of THRα1, THRα2 and THRβ1 is downregulated on protein level in mifepristone (RU 486) treated villous trophoblast tissue. In decidual tissue, we found a significant downregulation only for THRα1 in mifepristone treated tissue. On mRNA level, we also found a significantly reduced expression of THRA but no significant downregulation for THRB in placental tissue. The gene THRA encodes the isoform THRα and the gene THRB encodes the isoform THRβ. The majority of cells expressing the thyroid hormone receptors in the decidua are decidual stromal cells. In addition, in vitro experiments with trophoblast tumour cells showed that progesterone significantly induced THRA but not THRB expression.

CONCLUSIONS

Termination of pregnancy with mifepristone (RU 486) leads to a downregulation of THRα1, THRα2 and THRβ1 in villous trophoblasts and in addition to a decreased expression of THRA in placental tissue. Decreased expression of THRα1 induced by RU486 could also be found in the decidua. Therefore inhibition of the progesterone receptor may be responsible for this downregulation. This assumption is supported by the finding, that stimulation of the progesterone receptor by progesterone itself up-regulated THRA in trophoblast cells in vitro.

Expression of Thyroid Hormone Receptors in Villous Trophoblasts and Decidual Tissue at Protein and mRNA Levels Is Downregulated in Spontaneous and Recurrent Miscarriages

Thyroid hormones are essential for the maintenance of pregnancy, and a deficiency in maternal thyroid hormones has been associated with early pregnancy losses. The expression of THRα1, THRβ1 and THRα2 increases with gestational age. The aim of this study was the investigation of the protein and mRNA-levels of THR isoforms THRα1, THRα2, THRβ1 and THRβ2 in normal, spontaneous and recurrent miscarriages. The identification of THR-expressing cells in the decidua was done with double immunofluorescence. The nuclear expression of THRα1, THRα2, THRβ1 and THRβ2 is downregulated at protein level in spontaneous and recurrent miscarriages in villous trophoblast tissue. In decidual tissue, we found a significant downregulation only for THRα1 in spontaneous miscarriages. For recurrent miscarriages, THRα1 and THRβ1 were both significantly downregulated in decidual tissue. By applying HLA-G as a trophoblast marker, we found a significant co-expression only for THRβ2. The results of our study show that thyroid hormone receptors THRα1, THRα2, THRβ1 and THRβ2 are downregulated in spontaneous and recurrent miscarriages. The majority of cells expressing the thyroid hormone receptors in the decidua are decidual stromal cells.

Thyroid function in pregnancy and its influences on maternal and fetal outcomes

BACKGROUND

Maternal thyroid function alters during pregnancy. Inadequate adaptation to these changes results in thyroid dysfunction and pregnancy complications.

OBJECTIVES

This prospective study aimed to evaluate the prevalence of thyroid diseases in pregnancy and its outcomes in south of Iran.

MATERIALS AND METHODS

This prospective study was conducted on 600 healthy singleton pregnant women who aged 18 to 35 years old at 15 to 28 weeks of gestation. We investigated the prevalence of thyroid dysfunctions in women. Multivariate analysis was performed to determine the effect thyroid dysfunction on obstetric and neonatal outcome.

RESULTS

Thyroid stimulating hormone (TSH) levels of 0.51, 1.18, 1.68, 2.4, and 4.9 mIU/L were at 2.5th, 25th, 50th, 75th, and 97.5th percentile in our population. The prevalence of clinical hypothyroidism, subclinical hypothyroidism, overt hyperthyroidism, and subclinical hyperthyroidism in all pregnant women was 2.4%, 11.3%, 1.2%, and 0.3%, respectively. In addition, 1.4% of patients had isolated hypothyroxinemia. Clinical hypothyroidism was associated with increased risk of preterm delivery (P = 0.045). Subclinical hypothyroidism had a significant association with intrauterine growth restriction (IUGR) (P = 0.028) as well as low Apgar score at first minute (P = 0.022). Maternal hyperthyroidism was associated with IUGR (P = 0.048).

CONCLUSIONS

We revealed that thyroid dysfunction during pregnancy was associated with IUGR and low Apgar score even in subclinical forms. Further studies are required to determine whether early diagnosis and treatment of thyroid diseases, even in subclinical form, can prevent their adverse effect on fetus.

Thyroid hormone receptors and resistance to thyroid hormone disorders

Thyroid hormone action is predominantly mediated by thyroid hormone receptors (THRs), which are encoded by the thyroid hormone receptor α (THRA) and thyroid hormone receptor β (THRB) genes. Patients with mutations in THRB present with resistance to thyroid hormone β (RTHβ), which is a disorder characterized by elevated levels of thyroid hormone, normal or elevated levels of TSH and goitre. Mechanistic insights about the contributions of THRβ to various processes, including colour vision, development of the cochlea and the cerebellum, and normal functioning of the adult liver and heart, have been obtained by either introducing human THRB mutations into mice or by deletion of the mouse Thrb gene. The introduction of the same mutations that mimic human THRβ alterations into the mouse Thra and Thrb genes resulted in distinct phenotypes, which suggests that THRA and THRB might have non-overlapping functions in human physiology. These studies also suggested that THRA mutations might not be lethal. Seven patients with mutations in THRα have since been described. These patients have RTHα and presented with major abnormalities in growth and gastrointestinal function. The hypothalamic-pituitary-thyroid axis in these individuals is minimally affected, which suggests that the central T3 feedback loop is not impaired in patients with RTHα, in stark contrast to patients with RTHβ.

Molecular basis of thyrotropin and thyroid hormone action during implantation and early development

BACKGROUND

Implantation and early embryo development are finely regulated processes in which several molecules are involved. Evidence that thyroid hormones (TH: T4 and T3) might be part of this machinery is emerging. An increased demand for TH occurs during gestation, and any alteration in maternal thyroid physiology has significant implications for both maternal and fetal health. Not only overt but also subclinical hypothyroidism is associated with infertility as well as with obstetric complications, including disruptions and disorders of pregnancy, labor, delivery, and troubles in early neonatal life.

METHODS

We searched the PubMed and Google Scholar databases for articles related to TH action on ovary, endometrium, trophoblast maturation and embryo implantation. In addition, articles on the regulation of TH activity at cellular level have been reviewed. The findings are hereby summarized and critically discussed.

RESULTS

TH have been shown to influence endometrial, ovarian and placental physiology. TH receptors (TR) and thyrotropin (thyroid-stimulating hormone: TSH) receptors (TSHR) are widely expressed in the feto-maternal unit during implantation, and both the endometrium and the trophoblast might be influenced by TH either directly or through TH effects on the synthesis and activity of implantation-mediating molecules. Interestingly, due to the multiplicity of mechanisms involved in TH action (e.g. differential expression of TR isoforms, heterodimeric receptor partners, interacting cellular proteins, and regulating enzymes), the TH concentration in blood is not always predictive of their cellular availability and activity at both genomic and nongenomic level.

CONCLUSIONS

In addition to the known role of TH on the hormonal milieu of the ovarian follicle cycle, which is essential for a woman's fertility, evidence is emerging on the importance of TH signaling during implantation and early pregnancy. Based on recent observations, a local action of TH on female reproductive organs and the embryo during implantation appears to be crucial for a successful pregnancy. Furthermore, an imbalance in the spatio-temporal expression of factors involved in TH activity might induce early arrest of pregnancy in women considered as euthyroid, based on their hormonal blood concentration. In conclusion, alterations of the highly regulated local activity of TH may play a crucial, previously underestimated, role in early pregnancy and pregnancy loss. Further studies elucidating this topic should be encouraged.

Triiodothyronine regulates angiogenic growth factor and cytokine secretion by isolated human decidual cells in a cell-type specific and gestational age-dependent manner

STUDY QUESTION

Does triiodothyronine (T3) regulate the secretion of angiogenic growth factors and cytokines by human decidual cells isolated from early pregnancy?

SUMMARY ANSWER

T3 modulates the secretion of specific angiogenic growth factors and cytokines, with different regulatory patterns observed amongst various isolated subpopulations of human decidual cells and with a distinct change between the first and second trimesters of pregnancy.

WHAT IS KNOWN ALREADY

Maternal thyroid dysfunction during early pregnancy is associated with complications of malplacentation including miscarriage and pre-eclampsia. T3 regulates the proliferation and apoptosis of fetal-derived trophoblasts, as well as promotes the invasive capability of extravillous trophoblasts (EVT). We hypothesize that T3 may also have a direct impact on human maternal-derived decidual cells, which are known to exert paracrine regulation upon trophoblast behaviour and vascular development at the uteroplacental interface.

STUDY DESIGN, SIZE, DURATION

This laboratory-based study used human decidua from first (8–11 weeks; n = 18) and second (12–16 weeks; n = 12) trimester surgical terminations of apparently uncomplicated pregnancies.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Primary cultures of total decidual cells, and immunomagnetic bead-isolated populations of stromal-enriched (CD10+) and stromal-depleted (CD10−) cells, uterine natural killer cells (uNK cells; CD56+) and macrophages (CD14+) were assessed for thyroid hormone receptors and transporters by immunocytochemistry. Each cell population was treated with T3 (0, 1, 10, 100 nM) and assessments were made of cell viability (MTT assay) and angiogenic growth factor and cytokine secretion (immunomediated assay). The effect of decidual cell-conditioned media on EVT invasion through Matrigel^® was evaluated.

MAIN RESULTS AND THE ROLE OF CHANCE

Immunocytochemistry showed the expression of thyroid hormone transporters (MCT8, MCT10) and receptors (TRα1, TRβ1) required for thyroid hormone-responsiveness in uNK cells and macrophages from the first trimester. The viability of total decidual cells and the different cell isolates were unaffected by T3 so changes in cell numbers could not account for any observed effects. In the first trimester, T3 decreased VEGF-A secretion by total decidual cells (P < 0.05) and increased angiopoietin-2 secretion by stromal-depleted cells (P < 0.05) but in the second trimester total decidual cells showed only increased angiogenin secretion (P < 0.05). In the first trimester, T3 reduced IL-10 secretion by total decidual cells (P < 0.05), and reduced granulocyte macrophage colony stimulating factor (P < 0.01), IL-8 (P < 0.05), IL-10 (P < 0.01), IL-1β (P < 0.05) and monocyte chemotactic protein -1 (P < 0.001) secretion by macrophages, but increased tumour necrosis factor-α secretion by stromal-depleted cells (P < 0.05) and increased IL-6 by uNK cells (P < 0.05). In contrast, in the second trimester T3 increased IL-10 secretion by total decidual cells (P < 0.01) but did not affect cytokine secretion by uNK cells and macrophages. Conditioned media from first trimester T3-treated total decidual cells and macrophages did not alter EVT invasion compared with untreated controls. Thus, treatment of decidual cells with T3 resulted in changes in both angiogenic growth factor and cytokine secretion in a cell type-specific and gestational age-dependent manner, with first trimester decidual macrophages being the most responsive to T3 treatment, but these changes in decidual cell secretome did not affect EVT invasion in vitro.

LIMITATIONS, REASONS FOR CAUTION

Our results are based on in vitro findings and we cannot be certain if a similar response occurs in human pregnancy in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

Optimal maternal thyroid hormone concentrations could play a critical role in maintaining a balanced inflammatory response in early pregnancy to prevent fetal immune rejection and promote normal placental development through the regulation of the secretion of critical cytokines and angiogenic growth factors by human decidual cells. Our data suggest that there is an ontogenically determined regulatory ‘switch’ in T3 responsiveness between the first and second trimesters, and support the notion that the timely and early correction of maternal thyroid dysfunction is critical in influencing pregnancy outcomes.

STUDY FUNDING/COMPETING INTEREST(S)

This study is funded by Wellbeing of Women (RG/1082/09 to S.Y.C., M.D.K., J.A.F., L.S.L., G.E.L.) and Action Medical Research – Henry Smith Charity (SP4335 to M.D.K., S.Y.C., L.S.L., J.A.F.). The authors have no conflicts of interest to disclose.

MCT8 expression in human fetal cerebral cortex is reduced in severe intrauterine growth restriction

The importance of the thyroid hormone (TH) transporter, monocarboxylate transporter 8 (MCT8), to human neurodevelopment is highlighted by findings of severe global neurological impairment in subjects with MCT8 (SLC16A2) mutations. Intrauterine growth restriction (IUGR), usually due to uteroplacental failure, is associated with milder neurodevelopmental deficits, which have been partly attributed to dysregulated TH action in utero secondary to reduced circulating fetal TH concentrations and decreased cerebral thyroid hormone receptor expression. We postulate that altered MCT8 expression is implicated in this pathophysiology; therefore, in this study, we sought to quantify changes in cortical MCT8 expression with IUGR. First, MCT8 immunohistochemistry was performed on occipital and parietal cerebral cortex sections obtained from appropriately grown for gestational age (AGA) human fetuses between 19 weeks of gestation and term. Secondly, MCT8 immunostaining in the occipital cortex of stillborn IUGR human fetuses at 24-28 weeks of gestation was objectively compared with that in the occipital cortex of gestationally matched AGA fetuses. Fetuses demonstrated widespread MCT8 expression in neurons within the cortical plate and subplate, in the ventricular and subventricular zones, in the epithelium of the choroid plexus and ependyma, and in microvessel wall. When complicated by IUGR, fetuses showed a significant fivefold reduction in the percentage area of cortical plate immunostained for MCT8 compared with AGA fetuses (P<0.05), but there was no significant difference in the proportion of subplate microvessels immunostained. Cortical MCT8 expression was negatively correlated with the severity of IUGR indicated by the brain:liver weight ratios (r(2)=0.28; P<0.05) at post-mortem. Our results support the hypothesis that a reduction in MCT8 expression in the IUGR fetal brain could further compromise TH-dependent brain development.

Intrauterine growth retarded piglet as a model for humans--studies on the perinatal development of the gut structure and function

The overall acceptance of pig models for human biomedical studies is steadily growing. Results of rodent studies are usually confirmed in pigs before extrapolating them to humans. This applies particularly to gastrointestinal and metabolism research due to similarities between pig and human physiology. In this context, intrauterine growth retarded (IUGR) pig neonate can be regarded as a good model for the better understanding of the IUGR syndrome in humans. In pigs, the induction of IUGR syndrome may include maternal diet intervention, dexamethasone treatment or temporary reduction of blood supply. However, in pigs, like in humans, circa 8% of neonates develop IUGR syndrome spontaneously. Studies on the pig model have shown changes in gut structure, namely a reduced thickness of mucosa and muscle layers, and delayed kinetic of disappearance of vacuolated enterocytes were found in IUGR individuals in comparison with healthy ones. Functional changes include reduced dynamic of gut mucosa rebuilding, decreased activities of main brush border enzymes, and changes in the expression of proteins important for carbohydrate, amino acids, lipid, mineral and vitamin metabolism. Moreover, profiles of intestinal hormones are different in IUGR and non-IUGR piglets. It is suggested that supplementation of the mothers during the gestation and/or the IUGR offspring after birth can help in restoring the development of the gastrointestinal tract. The pig provides presumably the optimal animal model for humans to study gastrointestinal tract structure and function development in IUGR syndrome.

Monocarboxylate transporter 8 modulates the viability and invasive capacity of human placental cells and fetoplacental growth in mice

Monocarboxylate transporter 8 (MCT8) is a well-established thyroid hormone (TH) transporter. In humans, MCT8 mutations result in changes in circulating TH concentrations and X-linked severe global neurodevelopmental delay. MCT8 is expressed in the human placenta throughout gestation, with increased expression in trophoblast cells from growth-restricted pregnancies. We postulate that MCT8 plays an important role in placental development and transplacental TH transport. We investigated the effect of altering MCT8 expression in human trophoblast in vitro and in a Mct8 knockout mouse model. Silencing of endogenous MCT8 reduced T3 uptake into human extravillous trophoblast-like cells (SGHPL-4; 40%, P<0.05) and primary cytotrophoblast (15%, P<0.05). MCT8 over-expression transiently increased T3 uptake (SGHPL-4∶30%, P<0.05; cytotrophoblast: 15%, P<0.05). Silencing MCT8 did not significantly affect SGHPL-4 invasion, but with MCT8 over-expression T3 treatment promoted invasion compared with no T3 (3.3-fold; P<0.05). Furthermore, MCT8 silencing increased cytotrophoblast viability (∼20%, P<0.05) and MCT8 over-expression reduced cytotrophoblast viability independently of T3 (∼20%, P<0.05). In vivo, Mct8 knockout reduced fetal:placental weight ratios compared with wild-type controls at gestational day 18 (25%, P<0.05) but absolute fetal and placental weights were not significantly different. The volume fraction of the labyrinthine zone of the placenta, which facilitates maternal-fetal exchange, was reduced in Mct8 knockout placentae (10%, P<0.05). However, there was no effect on mouse placental cell proliferation in vivo. We conclude that MCT8 makes a significant contribution to T3 uptake into human trophoblast cells and has a role in modulating human trophoblast cell invasion and viability. In mice, Mct8 knockout has subtle effects upon fetoplacental growth and does not significantly affect placental cell viability probably due to compensatory mechanisms in vivo.

Postnatal leptin promotes organ maturation and development in IUGR piglets

Babies with intra-uterine growth restriction (IUGR) are at increased risk for experiencing negative neonatal outcomes due to their general developmental delay. The present study aimed to investigate the effects of a short postnatal leptin supply on the growth, structure, and functionality of several organs at weaning. IUGR piglets were injected from day 0 to day 5 with either 0.5 mg/kg/d leptin (IUGRLep) or saline (IUGRSal) and euthanized at day 21. Their organs were collected, weighed, and sampled for histological, biochemical, and immunohistochemical analyses. Leptin induced an increase in body weight and the relative weights of the liver, spleen, pancreas, kidneys, and small intestine without any changes in triglycerides, glucose and cholesterol levels. Notable structural and functional changes occurred in the ovaries, pancreas, and secondary lymphoid organs. The ovaries of IUGRLep piglets contained less oogonia but more oocytes enclosed in primordial and growing follicles than the ovaries of IUGRSal piglets, and FOXO3A staining grade was higher in the germ cells of IUGRLep piglets. Within the exocrine parenchyma of the pancreas, IUGRLep piglets presented a high rate of apoptotic cells associated with a higher trypsin activity. In the spleen and the Peyer's patches, B lymphocyte follicles were much larger in IUGRLep piglets than in IUGRSal piglets. Moreover, IUGRLep piglets showed numerous CD79(+) cells in well-differentiated follicle structures, suggesting a more mature immune system. This study highlights a new role for leptin in general developmental processes and may provide new insight into IUGR pathology.

Thyroid function in small for gestational age newborns: a review

Several studies have shown that small for gestational age (SGA) babies have a different hormonal profile than those born with a birth weight appropriate for gestational age (AGA). Thyroid hormones play an important role in growth and neurocognitive development. Only few studies analyzed the concentrations of thyroid-stimulating hormone (TSH) and thyroxine (T4) during fetal and extrauterine life in SGA and AGA newborns, and the existing data on the possible alterations of these hormones in postnatal life are controversial. It remains to be established whether SGA newborns have different blood concentrations of thyroid hormones as compared with AGA infants and if so, whether these findings play a role in the development of obesity, short stature, hypertension, and diabetes--disorders, already known to be related with SGA birth. It has also not yet been established whether and when substitutive therapy with levothyroxine (LT4) should be initiated in preterm and full-term SGA newborns. Further trials are needed to determine the thyroid hormone profile in both preterm and full-term SGA newborns and also to evaluate the effectiveness and safety of LT4 treatment in these infants.

Serum thyroid hormone levels in healthy children from birth to adulthood and in short children born small for gestational age

CONTEXT

Age-appropriate reference ranges for thyroid hormones are required for detecting pediatric thyroid dysfunction. Data on thyroid hormones and peripheral thyroid metabolism in short children born small for gestational age (SGA) before and during GH treatment are lacking.

OBJECTIVES

Our objectives were to obtain pediatric thyroid hormone reference ranges; to investigate thyroid hormones in short SGA children before puberty, during puberty, and during postponement of puberty by GnRH analog; and to evaluate thyroid hormones during GH treatment.

PATIENTS AND DESIGN

In 512 healthy children (225 females; 0-18 yr), free T(4) (FT(4)), TSH, total T(4), T(3), rT(3), and T(4)-binding globulin were determined. Reference ranges were calculated using the linearity, median, and skewness method. In 125 short SGA children (62 females; mean age 11.3 yr), thyroid hormones were analyzed before and after 2 yr of GH treatment and additional GnRH analog.

RESULTS

Thyroid references showed wide ranges postnatally and age-specific patterns thereafter, similar in boys and girls. Untreated short SGA children had similar FT(4) and T(4) levels as the reference population but significantly higher T(3), rT(3), and T(4)-binding globulin levels. During puberty and during GH treatment, FT(4) and rT(3) significantly decreased, whereas T(3) significantly increased.

CONCLUSION

Age-specific thyroid reference ranges are presented. Puberty and GH treatment both induce changes in peripheral thyroid metabolism, resulting in more biologically active T(3) at the expense of less inactive rT(3), possibly mediated by IGF-I. GH treatment induces altered peripheral thyroid metabolism but does not result in thyroid dysfunction.