Thyroxine values from newborn screening of 919 infants born before 29 weeks' gestation

Growth hormone promotes myelin repair after chronic hypoxia via triggering pericyte-dependent angiogenesis

White matter injury (WMI) causes oligodendrocyte precursor cell (OPC) differentiation arrest and functional deficits, with no effective therapies to date. Here, we report increased expression of growth hormone (GH) in the hypoxic neonatal mouse brain, a model of WMI. GH treatment during or post hypoxic exposure rescues hypoxia-induced hypomyelination and promotes functional recovery in adolescent mice. Single-cell sequencing reveals that Ghr mRNA expression is highly enriched in vascular cells. Cell-lineage labeling and tracing identify the GHR-expressing vascular cells as a subpopulation of pericytes. These cells display tip-cell-like morphology with kinetic polarized filopodia revealed by two-photon live imaging and seemingly direct blood vessel branching and bridging. Gain-of-function and loss-of-function experiments indicate that GHR signaling in pericytes is sufficient to modulate angiogenesis in neonatal brains, which enhances OPC differentiation and myelination indirectly. These findings demonstrate that targeting GHR and/or downstream effectors may represent a promising therapeutic strategy for WMI.

Thyroxine and Thyroid-Stimulating Hormone in Own Mother’s Milk, Donor Milk, and Infant Formula

Breastfeeding is widely supported in clinical and home practices, and it is known that different forms of infant feeding differ in hormone content. Thyroid hormones have essential physiological roles. In our study, we examined thyroid-stimulating hormone (TSH), thyroxine, and albumin levels in breast milk produced for term (n = 16) or preterm (n = 15) infants throughout the first 6 months of lactation. Moreover, we analyzed these components in donor human milk and in three different infant formulas. Term and preterm breast milk samples were collected monthly. The two groups had similar levels of TSH (18.4 ± 1.4 vs. 24.7 ± 2.9 nU/L), but term milk contained higher amounts of thyroxine (11,245.5 ± 73.8 vs. 671.6 ± 61.2 nmol/L) during the examination period. The albumin level was significantly higher in preterm breast milk than in term breast milk (328.6 ± 17.1 vs. 264.2 ± 6.8 mg/L). In preterm breast milk we detected downward trends in the levels of TSH (−30.2%) and thyroxine (−29.2%) in the 3rd through 6th month compared to the first 2 months of lactation. Microbiological safety of donor milk was ensured by Holder pasteurization (HoP). From the Breast Milk Collection Center of Pécs, Hungary, we enrolled 44 donor mothers into the study. HoP decreased TSH (−73.8%), thyroxine (−22.4%), and albumin (−20.9%) concentrations. Infant formulas used by the Neonatal Intensive Care Unit of the University of Pécs were found to not contain the investigated hormones, but their albumin levels were similar to the breast milk samples. The present study shows the lack of thyroid hormones in infant formulas compared to human milk and raises the question of whether formula-fed infants should be supplemented with thyroid hormones.

Effects of oral iodine supplementation in very low birth weight preterm infants for the prevention of thyroid function alterations during the neonatal period: results of a randomised assessor-blinded pilot trial and neurodevelopmental outcomes at 24 months

The trace element iodine (I) is essential for the synthesis of thyroid hormones. Parenteral nutrition solutions, formula milk, and human breast milk contain insufficient iodine to meet recommended intake for preterm infants. Iodine deficiency may affect thyroid function and may be associated with morbidity or neurological outcomes. The primary objective is to assess the evidence that dietary supplementation with iodine affects thyroid function during the neonatal period. The design was a randomised controlled pilot trial. Infants who met the inclusion criteria were enrolled through consecutive sampling and assigned to two different groups. The setting was a Spanish university hospital. Ninety-four patients with very low birth weight (under 1500 g) were included. Intervention group: 30 µg I/kg/day of iodine in oral drops given to 47 infants from their first day of life until hospital discharge. Control group: 47 infants without supplements. Formula and maternal milk samples for the determination of iodine content were collected at 1, 7, 15, 21, 30 days, and at discharge. Blood samples were collected for thyroid hormones. Neurological development was assessed at 2 years of age (Bayley III Test). Infants in the supplemented group reached the recommended levels from the first days of life. The researchers detected the effects of iodine balance on the plasma levels of thyroid hormones measured during the first 12 weeks of age. The trial assessed the impact of the intervention on neurodevelopmental morbidity.Conclusion: Thyroid function is related to iodine intake in preterm infants. Therefore, supplements should be added if iodine intake is found to be inadequate. The analyses found no effects of iodine supplementation on the composite scores for Bayley-III assessments in all major domains. The study results indicate potentially important effects on language development related to low iodine excretion during the first 4 weeks of life What is Known: • Thyroid function is related to iodine intake in preterm infants. • Preterm babies on formula preparations and with exclusive parenteral nutrition are at high risk of iodine deficiency. What is New: • Iodine intake should be monitored during the neonatal period. • Iodine supplements should be added if iodine intake is found to be inadequate.

Thyroid function and dysfunction in preterm infants-Challenges in evaluation, diagnosis and therapy

Thyroid hormone levels have a crucial role for optimal brain development from gestation through the first 2 postnatal years. However, thyroid hormones vary with gestational age, and their levels vary between term and preterm infants. Preterm newborns are prone to thyroid dysfunction which is now more frequently observed with the advances of neonatal care and improved survival of extremely premature infants. Thus, hypothyroxinaemia of prematurity associated with delayed TSH elevation is very common in low birth weight premature infants most likely due to the immaturity of the hypothalamic-pituitary thyroid axis. Furthermore, postnatal illness, medications and iodine status may contribute to the thyroid dysfunction or affect the interpretation of the thyroid function tests. Despite available guidelines, timing of screening and optimal treatment of thyroid dysfunction in premature infants remains controversial. Furthermore, it is unknown whether untreated thyroid dysfunction in premature babies affects neurodevelopmental outcome. In the vast majority of preterm infants, hypothyroxinaemia is transient; however, permanent hypothyroidism due to thyroid dysgenesis or enzyme defects might also occur. Therefore, careful monitoring of thyroid function and long-term follow-up is needed to assess an appropriate therapeutic approach. This article reviews thyroid physiology in preterm infants, the influences of gestation and other neonatal conditions on thyroid function tests, optimal timing of screening and possible predictors to differentiate transient hypothyroxinaemia from permanent hypothyroidism.

Pituitary Glycoprotein Hormones in Human Milk before and after Pasteurization or Refrigeration

Our aims were to investigate the presence of pituitary glycoprotein hormones in preterm and donor milk, and to examine the effects of Holder pasteurization and refrigeration on the levels of these hormones. We measured follicle-stimulating hormone (FSH), luteinizing hormone (LH), and thyroid-stimulating hormone (TSH) in milk samples from mothers who delivered prematurely (n = 27) and in samples of mothers who delivered at term and donated milk to the Mother's Milk Bank of Iowa (n = 30). The gonadotropins and TSH were present in similar amounts within human milk produced for preterm and term infants. FSH increased 21% after refrigeration (p < 0.05), while LH declined by 39% (p < 0.05). Holder pasteurization decreased LH by 24% (p < 0.05) and increased TSH by 17% (p < 0.05). Holder pasteurization followed by refrigeration resulted in a 21% increase in FSH and a 41% decrease in LH (both p < 0.05), resulting in more than a 3-fold increase in donor milk FSH:LH ratios (p < 0.05 versus fresh donor milk). Despite structural similarities, the gonadotropins are differentially impacted by Holder pasteurization and refrigeration, and this results in marked alterations in the relative amount of FSH and LH that may be administered to preterm infants, potentially swinging hormonal balance towards ovarian hyperstimulation in females and hypogonadism in males.

Lack of association between hypothyroxinemia of prematurity and transient thyroid abnormalities with adverse long term neurodevelopmental outcome in very low birth weight infants

Introduction

The association between hypothyroxinemia of prematurity with neurodevelopment was controversial.

Objectives

To compare 5 year neurodevelopmental outcomes of very low birth weight (VLBW) infants with hypothyroxinemia of prematurity against those without.

Methods

Retrospective cohort study in a single tertiary neonatal centre of VLBW infants born between the year 2008 to 2011. Comparisons were made between all abnormal and normal thyroid function controls using cord thyroid function tests, thyroid function tests during admission and pre-discharge thyroid function test done at term equivalent age. At 2 years corrected age, Bayley scales of infant and toddler development–third edition and Vineland II adaptive behaviour scales (VABS) were collected. At 5 years, Wechsler Preschool and Primary Scale of Intelligence (WPPSI-III), Bracken School Readiness Assessment, VABS and Beery Test of Visual-Motor Integration were collected.

Results

110 subjects were studied at 2 years corrected age and 80 subjects at 5 years old. 29 infants had abnormal thyroid function test (10 infants with hypothyroxinemia of prematurity and 19 infants with transient thyroid abnormalities). There were no significant difference in the 2 years and 5 years developmental outcome between infants with and without hypothyroxinemia of prematurity (p-value>0.05); and between infants with and without transient thyroid abnormalities (p-value>0.05). There were no significant difference in neurological, visual and hearing impairment between infants with or without hypothyroxinemia of prematurity (p-value>0.05).

Conclusions

Hypothyroxinemia of prematurity or transient thyroid abnormalities in VLBW infants were not associated with poorer neurodevelopment and did not support the need for levothyroxine supplementation.

Iodine supplementation for the prevention of mortality and adverse neurodevelopmental outcomes in preterm infants

BACKGROUND

Parenteral nutrition solutions, artificial formulas, and human breast milk contain insufficient iodine to meet recommended intakes for preterm infants. Iodine deficiency may exacerbate transient hypothyroxinaemia in preterm infants and this may be associated with adverse neonatal and longer-term outcomes.

OBJECTIVES

To assess the evidence from randomised controlled trials that dietary supplementation with iodine reduces mortality and morbidity in preterm infants.

SEARCH METHODS

We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials (CENTRAL 2018, Issue 1), Ovid MEDLINE, Ovid Embase, Ovid Maternity & Infant Care Database, and CINAHL to February 2018. We searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials that compared supplementing enteral or parenteral feeds with iodine (as iodide salt) versus placebo or no supplementation in preterm infants.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility and risk of bias, and extracted data. We analysed treatment effects as described in the individual trials and reported risk ratios (RR) and risk differences for dichotomous data, and mean differences (MD) for continuous data, with 95% confidence intervals (CI). We used a fixed-effect model in meta-analyses and planned to explore potential causes of heterogeneity in sensitivity analyses. We used the GRADE approach to assess the quality of evidence.

MAIN RESULTS

Two randomised controlled trials fulfilled the eligibility criteria. Both trials used methods to limit bias including allocation concealment and blinding of clinicians and investigators to the allocated intervention. The trials enrolled 1394 infants. One trial recruited 1273 participants. Most participants were born very preterm (less than 32 weeks' gestation) and about one-third were extremely preterm (less than 28 weeks' gestation). Analyses found no effect of iodine supplementation on mortality before hospital discharge (typical RR 1.01, 95% CI 0.72 to 1.42; 2 studies, 1380 infants) or on neurodevelopmental assessments at two years post-term (Bayley Scales of Infant and Toddler Development, Third Edition main domain composite scores: cognitive: MD -0.30, 95% CI -2.44 to 1.84; motor: MD 0.20, 95% CI -2.15 to 2.55; language: MD -0.10, 95% CI -2.50 to 2.30; 1 study, 1259 infants). There were no differences in the proportion of infants who died or had a composite score less than 85 in any main Bayley domain (RR 1.05, 95% CI 0.94 to 1.17; 1 study, 1259 infants), or had visual impairment (RR 0.63, 95% CI 0.28 to 1.45; 1 study, 1092 infants) or auditory impairment (RR 1.05, 95% CI 0.51 to 2.16; 1 study, 1093 infants). Using GRADE methods, we assessed the evidence for the effects on mortality and neurodevelopment outcomes as high-certainty.

AUTHORS' CONCLUSIONS

The available trial data, predominantly from one large, high-quality multicentre study published in 2017, do not show any evidence of beneficial effects of iodine supplementation for preterm infants. Given the high certainty of these estimates of effect, further trials of this intervention in this population are unlikely to be considered research priorities.

Late-onset circulatory collapse of prematurity

Late-onset circulatory collapse (LCC) is a refractory hypotension occurring after the early neonatal period (>day 7), in very low-birthweight infants. Typically, infants stabilized within the early neonatal period develop sudden onset of circulatory collapse after the early neonatal period. The underlying pathophysiology of LCC is considered to be relative adrenal insufficiency, which is well known in Japan, but is not widely accepted in North America or Europe. The current increase in LCC in Japan suggests that the principal trigger is related to recent trends in neonatal medicine and/or newly introduced treatments for preterm infants, but the pathophysiology has not been fully elucidated. In this review, based on current knowledge regarding LCC, the pathophysiology is discussed.

Nationwide Evaluation of Congenital Hypothyroidism Screening during Neonatal Extracorporeal Membrane Oxygenation

BACKGROUND

Thyroid hormone concentrations may deviate from normal values during critical illness. This condition is known as nonthyroidal illness syndrome (NTIS), and it can influence the results of screening for congenital hypothyroidism (CH) during neonatal extracorporeal membrane oxygenation (ECMO).

OBJECTIVES

To determine the incidence of aberrant CH screening results in ECMO-treated neonates, to identify possible determinants, and to follow up patients with abnormal thyroid hormone concentrations.

METHODS

In this retrospective cohort study, we included 168 ECMO-treated neonates admitted from 2004 to 2014 and screened by protocol and divided them into the following 3 groups: group 1 (screened during ECMO, n = 107), group 2 (screened shortly before ECMO, n = 26), and group 3 (screened shortly after ECMO, n = 35).

RESULTS

CH screening results were aberrant in 67.3% (72/107) of the neonates screened during ECMO, in 73.1% (19/26) of the neonates screened before ECMO, and in 31.4% (11/35) of the neonates screened after ECMO (p < 0.001). Of the neonates with an aberrant screening result, all but 2 (i.e. 98%) had a low thyroxine concentration with a normal thyrotropin concentration at screening, as is seen in NTIS. None was diagnosed with CH. Mortality did not significantly differ between neonates with an aberrant screening result (32.4%) and neonates with a normal screening result (22.7%; p = 0.18). Screening before ECMO (OR 5.92; 95% CI 1.93-18.20), screening during ECMO (OR 4.49; 95% CI 1.98-10.19), and a higher Pediatric Logistic Organ Dysfunction-2 score (OR 1.31; 95% CI 1.04-1.66) were associated with an aberrant screening result.

CONCLUSIONS

Aberrant CH screening results were found in most ECMO-treated neonates screened before or during ECMO, which is likely due to NTIS. Follow-up of thyroid hormone concentrations is best started after recovery from critical illness. Our results suggest that thyroxine therapy is not required during ECMO.

Response to thyrotropin-releasing hormone stimulation tests in preterm infants with transient hypothyroxinemia of prematurity

OBJECTIVE

Whether hormone supplementation is necessary for infants with transient hypothyroxinemia of prematurity (THOP) remains controversial, and further analysis of the hypothalamus-pituitary-thyroid axis of infants with THOP is necessary.

STUDY DESIGN

Thyrotropin-releasing hormone (TRH) stimulation tests were performed at 2 weeks of age in 50 infants with a gestational age of 30 weeks or less, and the data were analyzed retrospectively.

RESULT

Subjects were divided into three groups; group A consisted of euthyroid infants, group B consisted of infants with THOP and group C consisted of hypothyroid infants. The basal and peak thyroid-stimulating hormone level of group C in response to TRH stimulation tests was significantly higher than the others, but no differences were observed between groups A and B.

CONCLUSION

The response of infants with THOP to the TRH stimulation test was not different from that of euthyroid infants, which suggested that their hypothalamic-pituitary-thyroid axis was appropriately regulated in infants with THOP.

Establishing a reference range for triiodothyronine levels in preterm infants

OBJECTIVES

Thyroid dysfunction affects clinical complications in preterm infants and older children. However, thyroid hormone replacement in preterm infants has no proven benefits, possibly owing to the lack of an appropriate reference range for thyroid hormone levels. We aimed to establish a reference range for triiodothyronine (T3) levels at 1-month postnatal age (PNA) in preterm infants.

METHODS

This retrospective study included preterm infants born at a tertiary referral neonatal center at gestational age (GA)<35 weeks with no apparent thyroid dysfunction, for 6 consecutive years, with follow-up from PNA 2 weeks to 16 weeks. Using thyroid function tests (TFT), the relationships between T3 levels and thyrotropin (TSH) and free thyroxine (fT4) levels, birth weight, GA, postmenstrual age (PMA), and PNA were examined. The conversion trend for fT4 to T3 was analyzed using the T3/fT4 ratio.

RESULTS

Overall, 464 TFTs from 266 infants were analyzed, after excluding 65 infants with thyroid dysfunction. T3 levels increased with fT4 levels, birth weight, GA, PMA, and PNA but not with TSH levels. The T3/fT4 ratio also increased with GA, PNA, and PMA. The average T3 level at 1 month PNA was 72.56 ± 27.83 ng/dL, with significant stratifications by GA.

CONCLUSIONS

Relatively low T3 and fT4 levels in preterm infants were considered normal, with T3 levels and conversion trends increasing with GA, PMA, and PNA. Further studies are required to confirm the role of the present reference range in thyroid hormone replacement therapy.

The challenge of understanding cerebral white matter injury in the premature infant

White matter injury in the premature infant leads to motor and more commonly behavioral and cognitive problems that are a tremendous burden to society. While there has been much progress in understanding unique vulnerabilities of developing oligodendrocytes over the past 30years, there remain no proven therapies for the premature infant beyond supportive care. The lack of translational progress may be partially explained by the challenge of developing relevant animal models when the etiology remains unclear, as is the case in this disorder. There has been an emphasis on hypoxia-ischemia and infection/inflammation as upstream etiologies, but less consideration of other contributory factors. This review highlights the evolution of white matter pathology in the premature infant, discusses the prevailing proposed etiologies, critically analyzes a sampling of common animal models and provides detailed support for our hypothesis that nutritional and hormonal deprivation may be additional factors playing critical and overlooked roles in white matter pathology in the premature infant.

Reference range of thyroid hormones in very low birth weight infants at the time of discharge

AIM

There is little information regarding the reference range for thyroid hormones in preterm babies, especially those with very low birth weight (VLBW) of less than 1500 g. The objective of our study was to evaluate the relationship between thyroid hormone levels and postmenstrual age in a cohort of stable VLBW infants.

METHOD

An observational cohort study of VLBW infants preparing for discharge from a high-dependency nursery in Singapore. The infants' free thyroxine (fT4) and thyrotropin (TSH) levels were assayed just before discharge and correlated with postmenstrual age, calculated as the sum of the duration of gestation at birth and chronological age in weeks.

RESULTS

fT4 and TSH levels were sampled in 129 ex-VLBW babies at a mean postmenstrual age of 38.5 (±4.6) weeks. The babies were born at a mean±SD gestation of 28.9±2.4 weeks (median 29.0 weeks, range 24.0-34.5 weeks) with mean±SD birth weight of 1081±268 g (median 1090 g, range 490-1490 g). Linear regression analysis revealed negative and fair correlation between fT4 and postmenstrual age (r=-0.302). The mean±SD fT4 level was 16.8±3.2 pmol/L (median 16.8 pmol/L, range 8.5-28.9 pmol/L). However, there was only a very weak negative correlation between TSH levels and postmenstrual age, both with (r=-0.116) or without logarithmic transformation. The mean±SD TSH was 4.56±2.50 mIU/L (median 4.42 mIU/L, range 1.0-13.5 mIU/L).

CONCLUSION

Our study shows a fair and inverse correlation of fT4 with postmenstrual age in a large cohort of growing ex-VLBW infants, in keeping with maturation of the hypothalamic-pituitary-thyroid axis. It suggests that fT4 levels in growing infants are best compared to postmenstrual age-specific norms instead of a single reference interval.

Thyroid hormone transporters and deiodinases in the developing human hypothalamus

OBJECTIVE

Thyroid hormone (TH) signaling in brain cells is dependent on transport of TH across the plasma membrane followed by intracellular deiodination and binding to the nuclear TH receptors. The aim of this study is to investigate the expression of the specific TH transporters monocarboxylate transporter 8 (MCT8 (SLC16A2)), MCT10, organic anion transporting polypeptide 1C1 (OATP1C1 (SLCO1C1)), and the types 2 and 3 deiodinases (D2 and D3) in the developing human hypothalamus.

DESIGN

Fifteen postmortem brain samples of fetuses and young children ranging between 17 weeks of gestation and 29 months of postnatal age including one child (28 months) with central congenital hypothyroidism were studied.

METHODS

Sections of the different hypothalami were stained with polyclonal rabbit antisera against MCT8, MCT10, OATP1C1, D2, and D3.

RESULTS

We found MCT8 and D3 but not D2 protein expression to be present in our earliest sample of 17 weeks of gestation, indicating triiodothyronine degradation, but not production at this time of development. At term, expression of TH transporters and D2 decreased and D3 expression increased, suggesting decreased TH signaling just before birth. The child with central congenital hypothyroidism showed higher MCT8 and D2 expression compared with the other children of similar age.

CONCLUSIONS

This study reports the developmental timing of expression of components crucial for central TH signaling in the human hypothalamus. In general, during fetal hypothalamic development, the coordinated expression of D2 and D3 in combination with the different TH transporters suggests that proper TH concentrations are regulated to prevent untimely maturation of brain cells.

Low iodine content in the diets of hospitalized preterm infants

CONTEXT

Iodine is critical for normal thyroid hormone synthesis and brain development during infancy, and preterm infants are particularly vulnerable to the effects of both iodine deficiency and excess. Use of iodine-containing skin antiseptics in intensive care nurseries has declined substantially in recent years, but whether the current dietary iodine intake meets the requirement for hospitalized preterm infants is unknown.

OBJECTIVE

The aim of the study was to measure the iodine content of enteral and parenteral nutrition products commonly used for hospitalized preterm infants and estimate the daily iodine intake for a hypothetical 1-kg infant.

METHODS

We used mass spectrometry to measure the iodine concentration of seven preterm infant formulas, 10 samples of pooled donor human milk, two human milk fortifiers (HMF) and other enteral supplements, and a parenteral amino acid solution and soy-based lipid emulsion. We calculated the iodine provided by typical diets based on 150 ml/kg · d of formula, donor human milk with or without HMF, and parenteral nutrition.

RESULTS

Preterm formula provided 16.4-28.5 μg/d of iodine, whereas unfortified donor human milk provided only 5.0-17.6 μg/d. Adding two servings (six packets) of Similac HMF to human milk increased iodine intake by 11.7 μg/d, whereas adding two servings of Enfamil HMF increased iodine intake by only 0.9 μg/d. The other enteral supplements contained almost no iodine, nor did a parenteral nutrition-based diet.

CONCLUSIONS

Typical enteral diets for hospitalized preterm infants, particularly those based on donor human milk, provide less than the recommended 30 μg/d of iodine, and parenteral nutrition provides almost no iodine. Additional iodine fortification should be considered.

Multivariate analyses of factors that affect neonatal screening thyroid stimulating hormone

AIMS

All screening programmes in the UK use a primary thyroid stimulating hormone (TSH) screen for congenital hypothyroidism. Recent attention has been paid to aspects of screening, such as the relation between blood spot TSH levels and birth weight or gestational age. The aim of our study was to determine the factors affecting screening neonatal TSH levels.

METHODS

We conducted a retrospective analysis of blood spot screening TSH levels of all infants screened at a single regional screening laboratory.

RESULTS

There were 6498 infants screened during a 12-week period. Screening TSH level showed negative correlation with gestational age and birth weight. Multiple linear regression analysis revealed low birth weight as the only independent factor affecting screening TSH level.

CONCLUSIONS

Low birth weight infants appear to be at risk of thyroidal dysfunction. Our study showed that there were clinically significant but weak correlation between higher screening TSH levels and low birth weight. The clinical importance of these findings requires larger prospective studies to further elucidate the relevance of these factors affecting TSH screening levels.

Neurodevelopment of preterm infants born at 28 to 36 weeks of gestational age: the role of hypothyroxinemia and long-term outcome at 4 years

CONTEXT

Hypothyroxinemia in premature neonates may affect long-term neurodevelopment.

OBJECTIVE

This study aimed to examine the effects of hypothyroxinemia of the newborn preterm infants born at 28-36 weeks of gestational age (GA) on the neurodevelopment at 4 years of age.

PATIENTS

Prospective observational cohort study conducted in Madrid, Spain. Forty-six preterm infants were included in the study.

MAIN OUTCOME

The effects of the exposure to neonatal hypothyroxinemia on mental development were examined.

RESULTS

Using regression analyses we found that neonatal T4 had a positive association with general cognitive index and Verbal index, and neonatal FT4 with general cognitive and Memory indexes at 4 years of age.

CONCLUSIONS

The exposure to hypothyroxinemia during the neonatal period of late preterm infants may play role in neurodevelopmental delays. Higher T4 level means a trend to higher indexes and low T4 level means a lower neurodevelopmental indexes at 4 years of age.

Update on some aspects of neonatal thyroid disease

This article explores the basic development and pathophysiology of the thyroid gland. New factors in the normal development of the thyroid in the neonate are mentioned. The incidence of congenital hypothyroidism continues to increase. We describe congenital hypothyroidism, its possible etiologies, treatment and outcomes. We explore hypothyroxinanemia in pre−term neonates and the risk/benefit of prophylactic thyroid hormone replacement. We discuss the late rise of thyrotropin (TSH) in ill infants and those with very low birth weight. Ill infants or those born premature should have their thyroid function tests routinely monitored. On the occasion of borderline thyroid function test results, TRH testing can be useful in identifying those infants with either persistent or transient hypothyroidism. TRH testing is also helpful in identifying those patients with secondary hypothyroidism. With the early identification and prompt and proper treatment, neonates with congenital hypothyroidism, transient or persistent, should have positive long−term outcomes.

Conflict of interest:None declared.

Iodine in enteral and parenteral nutrition

Iodine deficiency (ID) has multiple adverse effects on growth and development due to inadequate thyroid hormone production. Methods for assessment of iodine nutrition in individuals include the urinary iodine concentration (UI), thyroid size and thyroid function tests. The UI measured in several repeat 24-h urine samples can detect inadequate iodine intake in individuals receiving enteral or parenteral nutrition (PN) and allow for iodine supplementation before the onset of hypothyroidism. A daily dose of 1 microg iodine/kg body weight is currently recommended for children receiving PN, but this is far below their requirements. Daily iodine requirements in adults receiving enteral nutrition or PN are estimated to be 70-150 microg, but most PN formulations do not contain iodine. Despite this, ID has been unlikely because absorption from iodine-containing skin antiseptics and other adventitious sources can provide sufficient iodine. However, if chlorhexidine replaces iodine-containing antiseptics for catheter care, ID may occur during long-term PN, and periodic testing of UI and thyroid function may be prudent. Infants may be particularly vulnerable to ID because of their small thyroidal iodine store. In this review, we describe three recent patients (an infant, a child and an adult) who developed ID and thyroid hypofunction during PN.

Phase 1 trial of 4 thyroid hormone regimens for transient hypothyroxinemia in neonates of <28 weeks' gestation

BACKGROUND

Transiently low levels of thyroid hormones occur in approximately 50% of neonates born 24-28 weeks' gestation and are associated with higher rates of cerebral palsy and cognitive impairment. Raising hormone levels shows promise for improving neurodevelopmental outcome.

OBJECTIVE

To identify whether any of 4 thyroid hormone supplementation regimens could raise T(4) and FT(4) without suppressing TSH (biochemical euthyroidism).

METHODS

Eligible subjects had gestational ages between 24 07 and 2767 weeks and were randomized <24 hours of birth to one of six study arms (n = 20-27 per arm): placebo (vehicle: 5% dextrose), potassium iodide (30 microg/kg/d) and continuous or bolus daily infusions of either 4 or 8 microg/kg/d of T(4) for 42 days. T(4) was accompanied by 1 microg/kg/d T(3) during the first 14 postnatal days and infused with 1 mg/mL albumin to prevent adherence to plastic tubing.

RESULTS

FT(4) was elevated in the first 7 days in all hormone-treated subjects; however, only the continuous 8 microg/kg/d treatment arm showed a significant elevation in all treatment epochs (P < .002 versus all other groups). TT(4) remained elevated in the first 7 days in all hormone-treated subjects (P < .05 versus placebo or iodine arms). After 14 days, both 8 microg/kg/d arms as well as the continuous 4 microg/kg/d arm produced a sustained elevation of the mean and median TT(4), >7 microg/dL (90 nM/L; P < .002 versus placebo). The least suppression of THS was achieved in the 4 microg/kg/d T(4) continuous infusion arm. Although not pre-hypothesized, the duration of mechanical ventilation was significantly lower in the continuous 4 microg/kg/d T(4) arm and in the 8 microg/kg/d T(4) bolus arm (P < .05 versus remaining arms). ROP was significantly lower in the combined 4 thyroid hormone treatment arms than in the combined placebo and iodine arms (P < .04). NEC was higher in the combined 8 microg/kg/d arms (P < .05 versus other arms).

CONCLUSIONS

Elevation of TT(4) with only modest suppression of TSH was associated with trends suggesting clinical benefits using a continuous supplement of low-dose thyroid hormone (4 microg/kg/d) for 42 days. Future trials will be needed to assess the long-term neurodevelopmental effects of such supplementation.

Iodine deficiency

Iodine deficiency has multiple adverse effects in humans, termed iodine deficiency disorders, due to inadequate thyroid hormone production. Globally, it is estimated that 2 billion individuals have an insufficient iodine intake, and South Asia and sub-Saharan Africa are particularly affected. However, about 50% of Europe remains mildly iodine deficient, and iodine intakes in other industrialized countries, including the United States and Australia, have fallen in recent years. Iodine deficiency during pregnancy and infancy may impair growth and neurodevelopment of the offspring and increase infant mortality. Deficiency during childhood reduces somatic growth and cognitive and motor function. Assessment methods include urinary iodine concentration, goiter, newborn TSH, and blood thyroglobulin. But assessment of iodine status in pregnancy is difficult, and it remains unclear whether iodine intakes are sufficient in this group, leading to calls for iodine supplementation during pregnancy in several industrialized countries. In most countries, the best strategy to control iodine deficiency in populations is carefully monitored universal salt iodization, one of the most cost-effective ways to contribute to economic and social development. Achieving optimal iodine intakes from iodized salt (in the range of 150-250 microg/d for adults) may minimize the amount of thyroid dysfunction in populations. Ensuring adequate iodine status during parenteral nutrition has become important, particularly in preterm infants, as the use of povidone-iodine disinfectants has declined. Introduction of iodized salt to regions of chronic iodine deficiency may transiently increase the incidence of thyroid disorders, but overall, the relatively small risks of iodine excess are far outweighed by the substantial risks of iodine deficiency.

Thyroid function in preterm infants 27-29 weeks of gestational age during the first four months of life: results from a prospective study comprising 80 preterm infants

AIM

Assessment of thyroid function in preterm neonates (PTN) 27-29 weeks of gestational age.

PATIENTS AND METHODS

80 PTN, gestational age 27 weeks in 24, 28 weeks in 28, and 29 weeks in 28. Neonates were classified as healthy (n=17) or sick (n=63). Measurement of serum TSH, free T4, T4, T3 and rT3 in the mother and in the cord at the time of delivery, and in the infant at 1 hour, 24 hours, 1 week, 3 weeks, and 2 and 4 months of postnatal age.

RESULTS

In healthy and sick preterms, TSH values peaked at 1 hour and decreased thereafter. Healthy PTN presented a peak in free T4 values at 24 hours that was not observed in sick neonates. Sick PTN had a lower TSH peak and lower free T4 values at 24 hours and 1 week than healthy ones (p < 0.05). Healthy PTN 27-29 weeks had lower TSH peak at 1 hour and lower free T4, T3 and T4 values during the first 2 months than healthy PTN 30-35 weeks (PTN30-35w) previously evaluated (p < 0.05). However, at all postnatal times healthy preterms had free T4 values above -2 SD of the mean values of healthy PTN30-35w. A wide range of free T4 values was observed in the sick group. Free T4 values above -2 SD of the mean values of healthy PTN30-35w were detected in a high proportion of sick PTN (58.3% at 24 hours, 73.5% at 1 week, 93.9% at 3 weeks, 85.1% at 2 months and 100% at 4 months).

CONCLUSIONS

Prematurity and disease influence thyroid function, and consequently thyroid function should be individually assessed in preterms 27-29 weeks of gestation during the first 2 months of life.

General background on the hypothalamic-pituitary-thyroid (HPT) axis

This article reviews the thyroid system, mainly from a mammalian standpoint. However, the thyroid system is highly conserved among vertebrate species, so the general information on thyroid hormone production and feedback through the hypothalamic-pituitary-thyroid (HPT) axis should be considered for all vertebrates, while species-specific differences are highlighted in the individual articles. This background article begins by outlining the HPT axis with its components and functions. For example, it describes the thyroid gland, its structure and development, how thyroid hormones are synthesized and regulated, the role of iodine in thyroid hormone synthesis, and finally how the thyroid hormones are released from the thyroid gland. It then progresses to detail areas within the thyroid system where disruption could occur or is already known to occur. It describes how thyroid hormone is transported in the serum and into the tissues on a cellular level, and how thyroid hormone is metabolized. There is an in-depth description of the alpha and beta thyroid hormone receptors and their functions, including how they are regulated, and what has been learned from the receptor knockout mouse models. The nongenomic actions of thyroid hormone are also described, such as in glucose uptake, mitochondrial effects, and its role in actin polymerization and vesicular recycling. The article discusses the concept of compensation within the HPT axis and how this fits into the paradigms that exist in thyroid toxicology/endocrinology. There is a section on thyroid hormone and its role in mammalian development: specifically, how it affects brain development when there is disruption to the maternal, the fetal, the newborn (congenital), or the infant thyroid system. Thyroid function during pregnancy is critical to normal development of the fetus, and several spontaneous mutant mouse lines are described that provide research tools to understand the mechanisms of thyroid hormone during mammalian brain development. Overall this article provides a basic understanding of the thyroid system and its components. The complexity of the thyroid system is clearly demonstrated, as are new areas of research on thyroid hormone physiology and thyroid hormone action developing within the field of thyroid endocrinology. This review provides the background necessary to review the current assays and endpoints described in the following articles for rodents, fishes, amphibians, and birds.

Prophylactic postnatal thyroid hormones for prevention of morbidity and mortality in preterm infants

BACKGROUND

Observational studies have shown an association between transiently low thyroid hormone levels in preterm infants in the first weeks of life (transient hypothyroxinaemia) and abnormal neurodevelopmental outcome. Thyroid hormone replacement might prevent this.

OBJECTIVES

To determine whether prophylactic thyroid hormones given to preterm infants without congenital hypothyroidism result in clinically important changes in neonatal and long term outcomes.

SEARCH STRATEGY

The standard search strategy of the Neonatal Review Group was used. This included searches of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2006), MEDLINE (1966 - March 2006), EMBASE, PREMEDLINE, and searches of abstracts of conference proceedings, citations of published articles and expert informants.

SELECTION CRITERIA

All trials using random or quasi-random patient allocation in which prophylactic thyroid hormone treatment was compared to control in premature infants.

DATA COLLECTION AND ANALYSIS

Assessment of trial quality, data extraction and synthesis of data, using relative risk (RR) and weighted mean difference (WMD), were performed using standard methods of the Cochrane Collaboration and its Neonatal Review Group.

MAIN RESULTS

Four studies enrolling 318 infants were included. All studies enrolled preterm infants on the basis of gestational age criteria. All studies commenced treatment in the first 48 hours, but used different regimens, dose and durations of treatment. All four studies used thyroxine (T4). Valerio 2004 incorporated one arm with an early short course of T3, then T4 for 6 weeks. Only two studies with neurodevelopmental follow-up were of good methodology (van Wassenaer 1997; Vanhole 1997). All studies were small with the largest (van Wassenaer 1997) enrolling 200 infants.No significant difference was found in neonatal morbidity, mortality or neurodevelopmental outcome in infants who received thyroid hormones compared to control. van Wassenaer 1997 reported no significant difference in abnormal mental development at 6, 12, 24 months (RR 0.67, 95% CI 0.28, 1.56) or five years (RR 0.66, 95% CI 0.22, 1.99) or cerebral palsy assessed at five years (RR 0.72, 95% CI 0.28, 1.84). Meta-analysis of two studies (van Wassenaer 1997, Vanhole 1997) found no significant difference in the Bayley MDI (WMD -1.14, 95% CI -5.46, 3.19) and PDI (WMD 0.22, 95% CI -4.80, 5.24) at 7 - 12 months. van Wassenaer 1997 reported no significant difference in the Bayley MDI (MD -3.50, 95% CI -11.21, 4.21) and PDI (MD 3.10, 95% CI -3.31, 9.51) at 24 months, IQ scores at 5 years (MD -2.10, 95% CI -7.91, 3.71) and children in special schooling at 10 years (RR 0.88, 95% CI 0.43, 1.83). Meta-analysis of all four trials found no significant difference in mortality to discharge (typical RR 0.76, 95% CI 0.46 to 1.24). van Wassenaer 1997 reported no significant difference in death or cerebral palsy at five years (RR 0.70, 95% CI 0.43 to 1.14). No significant differences were reported for neonatal morbidities, including the need for mechanical ventilation, duration of mechanical ventilation, air leak, CLD in survivors at 28 days or 36 weeks, intraventricular haemorrhage, severe intraventricular haemorrhage, periventricular leucomalacia, patent ductus arteriosus, sepsis, necrotising enterocolitis or retinopathy of prematurity.

AUTHORS' CONCLUSIONS

This review does not support the use of prophylactic thyroid hormones in preterm infants to reduce neonatal mortality, neonatal morbidity or improve neurodevelopmental outcomes. An adequately powered clinical trial of thyroid hormone supplementation with the goal of preventing the postnatal nadir of thyroid hormone levels seen in very preterm infants is required.

Postnatal thyroid hormones for preterm infants with transient hypothyroxinaemia

BACKGROUND

Extremely premature infants are at risk of transient hypothyroxinaemia in the first weeks after birth. These low thyroid hormone levels are associated with an increased incidence of neonatal morbidity, mortality and longer term developmental impairments. Thyroid hormone therapy might prevent these problems.

OBJECTIVES

To determine the evidence for thyroid hormone therapy in preterm infants with transient hypothyroxinaemia (low thyroid hormone level, normal TSH) for improvement of neonatal outcomes and neurodevelopment.

SEARCH STRATEGY

Searches were performed of The Cochrane Central Register of Controlled (CENTRAL, The Cochrane Library, Issue 1, 2006), MEDLINE (1966 - March 2006), PREMEDLINE (March 2006), EMBASE (1980 - March 2006), previous reviews including cross references, abstracts and conference proceedings, supplemented by requests to expert informants.

SELECTION CRITERIA

Trials enrolling preterm infants with transient hypothyroxinaemia (low thyroid hormone level, normal TSH level) in the neonatal period, using random or quasi-random patient allocation to thyroid hormone therapy compared to control (placebo or no treatment).

DATA COLLECTION AND ANALYSIS

Independent assessment of trial quality and data extraction by each review author. Synthesis of data using relative risk (RR) and weighted mean difference (WMD) using standard methods of the Cochrane Collaboration and its Neonatal Review Group.

MAIN RESULTS

Only one study was eligible. Chowdhry (1984) enrolled 23 infants < 1250 g and 25 - 28 weeks gestation with transient hypothyroxinaemia (serum total T4 </=4 mug/dl and TSH </= 20 IU/L). Infants were randomised to thyroxine 10 mug/kg/day or placebo beginning on day 15 and continuing daily for seven weeks. Chowdhry (1984) reported no neonatal mortality and one infant death in each group prior to discharge. No significant difference was reported in CLD at 28 days or 36 weeks, patent ductus arteriosus, necrotising enterocolitis, retinopathy or prematurity, weight gain, growth in head circumference or length. No significant difference was reported for mean T4 levels between thyroxine and placebo treated infants on day 21, 35, 49, 63 and 77 after birth. Free T4 was not measured. Neurodevelopmental follow up was inadequate to draw any conclusions from.

AUTHORS' CONCLUSIONS

There is insufficient evidence to determine whether use of thyroid hormones for treatment of preterm infants with transient hypothyroxinaemia results in changes in neonatal morbidity and mortality, or reductions in neurodevelopmental impairments. Further research is required.

Iodine supplementation for the prevention of mortality and adverse neurodevelopmental outcomes in preterm infants

BACKGROUND

Parenteral nutrition solutions, formula milks, and human breast milk contain insufficient iodine to meet recommended intakes for preterm infants. Iodine deficiency may exacerbate transient hypothyroxinaemia in preterm infants and this may be associated with adverse respiratory or neurological outcomes.

OBJECTIVES

To assess the evidence from randomised controlled trials that dietary supplementation with iodine reduces mortality and morbidity in preterm infants.

SEARCH STRATEGY

We used the standard search strategy of the Cochrane Neonatal Review Group. This included searches of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 4, 2005), MEDLINE (1966 - November 2005), EMBASE (1980 - November 2005), CINAHL (1982 - November 2005), conference proceedings, and previous reviews.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials that compared a policy of supplementing enteral or parenteral feeds with iodine (more than 30 micrograms per kilogram per day) versus placebo or no supplementation in preterm infants.

DATA COLLECTION AND ANALYSIS

The standard methods of the Cochrane Neonatal Review Group, with separate evaluation of trial quality and data extraction by two reviewers, and synthesis of data using relative risk, risk difference and weighted mean difference. The primary outcomes for this review were neonatal mortality, death before hospital discharge, and longer term neurodevelopmental outcomes including severe neurodevelopmental disability.

MAIN RESULTS

We found only one randomised controlled trial (N = 121) that fulfilled the review eligibility criteria (Rogahn 2000). The participants were infants born before 33 weeks' gestation (but most were of birth weight greater than 1000 grams). The primary aim of this trial was to assess the effect of iodine supplementation on thyroid function. The investigators did not detect any statistically significant effects on the plasma levels of thyroxine (free and total), triiodothyronine, or thyrotrophin in preterm infants (measured up to 40 weeks' post-conceptional age). Only one infant died and the trial was therefore underpowered to detect an effect on mortality. The trial did not assess the effect of the intervention on neurodevelopmental morbidity. There was not a statistically significant difference in the incidence of chronic lung disease.

AUTHORS' CONCLUSIONS

There are insufficient data at present to determine whether providing preterm infants with supplemental iodine (to match fetal accretion rates) prevents morbidity and mortality in preterm infants. Future randomised controlled trials of iodine supplementation should focus on extremely preterm and extremely low birth weight infants, the group at greatest risk of transient hypothyroxinaemia. These trials should aim to assess the effect of iodine supplementation on clinically important outcomes including respiratory morbidity and longer term neurodevelopment.

Absence of pestivirus antigen in brains with white matter damage

We previously suggested that antenatal pestivirus infection might play a role in the pathogenesis of perinatal brain white matter damage (WMD) in preterm infants. We have now examined 22 brains from stillborns and deceased newborns (both preterm and term) for the presence of bovine virus diarrhoea virus (BVDV) antigen. The brains of five females and five males with WMD (median gestational age 36.5wks), and nine female and three male controls (median gestational age 36.5wks) were used in the study. No BVDV antigen was detected in any of the 22 brains. We conclude that brain infection with BVDV is unlikely to play a role in WMD pathogenesis among preterm or term newborns. Further research is needed to test the hypothesis that intrauterine exposure to pestivirus antigen elicits a fetal inflammatory response which then contributes to WMD.

Antenatal Glucocorticoids Increase Early Total Thyroxine Levels in Premature Infants

BACKGROUND

Hypothyroxinemia is associated with adverse neonatal outcomes including white matter damage, cerebral palsy, poor neurodevelopment and death. It has become increasingly important to understand the natural history and modifiers of thyroid function in the premature infant. It is standard obstetrical practice to offer antenatal glucocorticoids to pregnant women with threatened preterm delivery. Few studies have investigated the effect of antenatal glucocorticoids on neonatal thyroid function.

OBJECTIVE

To examine the association between antenatal exposure to glucocorticoids and early total thyroxine (T4) levels among extremely premature infants.

METHODS

We studied 521 infants born at 4 medical centers. Entry criteria included a gestational age of 23-28 weeks and a serum thyroxine level obtained in the first postnatal week. Receipt of antenatal glucocorticoids was recorded as none, partial, or complete. A complete course consisted of two doses of betamethasone or four doses of dexamethasone within a 48-hour period between 2 and 7 days of delivery. Early total T4 levels were obtained from state-mandated newborn screening programs.

RESULTS

Controlling for potential maternal, perinatal and neonatal confounding variables, infants exposed to a complete course of antenatal glucocorticoids had total T4 levels 0.8 microg/dl higher than their peers who were not exposed to a complete course of antenatal glucocorticoids (p = 0.03).

CONCLUSIONS

Extremely premature infants who received a complete course of antenatal glucocorticoids had significantly higher total thyroxine levels in the first postnatal week. Maternal, perinatal, and early neonatal variables did not completely explain this association. We speculate that antenatal glucocorticoids influence early neonatal thyroid function.

Dopamine infusion and hypothyroxinaemia in very low birth weight preterm infants

The purpose of this study was to assess the relationship between transient hypothyroxinaemia of prematurity (THOP) in very low birth weight newborns and dopamine administration. A total of 172 newborns was enrolled in a prospective observational study and divided into three groups: group A included newborns who were never treated with dopamine; group B were infants in whom dopamine treatment was discontinued for at least 6 h before the congenital hypothyroidism screening and group C included infants who were given dopamine during the screening. Among those newborns given dopamine, the THOP incidence was higher (11.6% in group A; 53.8% in group B; 89.3% in group C), and the vales of TSH (1.67+/-2.32 microU/ml in group A; 1.29+/-1.74 microU/ml in group B; 0.89+/-1.34 microU/ml in group C) and thyroxine (6.1+/-2.2 microg/dl in group A; 3.9+/-1.9 microg/dl in group B; 2.4+/-1.4 microg/dl in group C) were significantly lower. These differences were further confirmed even after gestational age stratification and mathematical correction for differences in clinical conditions. The effects of dopamine appear to be dose-dependent.

CONCLUSION

Even if it cannot be excluded that reduced thyroid stimulating hormone and thyroxine concentrations are caused by non-thyroidal illness, the results suggest that the infusion of dopamine reduces the thyroid stimulating hormone and thyroxine levels in very low birth weight newborns.

A neonatal screening in Lebanon: Results of five years' experience

BACKGROUND

Neonatal screening programs for common disorders like phenylketonuria, congenital hypothyroidism, and glucose-6-phosphate dehydrogenase (G6PD) deficiency are not fully established at the national level in Lebanon. Screening for the above disorders was carried out for newborns delivered at the American University of Beirut Medical Center over a period of five years.

SUBJECTS AND METHODS

Blood specimens collected 2-3 days after birth were applied to neonatal screening blood collection cards. A total of 9117 newborns were screened using phenylalanine, thyroid-stimulating hormone, and G6PD activity measurements on blood spots.

RESULTS

One case of phenylketonuria and another of hyperphenylalaninemia were detected. We also detected 5 cases of permanent type of congenital hypothyroidism, giving an incidence of 5:9117 (1:1823). The age range at initiation of hormonal replacement therapy was 9-46 days. The overall incidence of G6PD was 106:9117 (1:86 or 1.16%), of which 84 had complete deficiency (1:109 or 0.92%), and 22 with intermediate activity.

CONCLUSION

The incidence of these disorders found in this Lebanese sub-population warrants consideration of a comprehensive nationwide neonatal screening program.

Treatment of transient hypothyroxinemia of prematurity: a survey of neonatal practice

We mailed a survey on treatment practices for transient hypothyroxinemia of prematurity (THOP) to 100 randomly selected neonatologists. In the year before the survey, 13 of 62 respondents (21.0%) had treated an average of 4.5 THOP patients with thyroid hormone, and 3 had treated 10 or more patients. Randomized trials assessing the value of thyroid supplementation in THOP are urgently needed.

Action of thyroid hormone in brain

Among the most critical actions of thyroid hormone in man and other mammals are those exerted on brain development. Severe hypothyroidism during the neonatal period leads to structural alterations, including hypomyelination and defects of cell migration and differentiation, with long-lasting, irreversible effects on behavior and performance. A complex regulatory mechanism operates in brain involving regulation of the concentration of the active hormone, T3, and the control of gene expression. Most brain T3 is formed locally from its precursor, T4, by the action of type II deiodinase which is expressed in glial cells, tanycytes, and astrocytes. Type III deiodinase (DIII) is also involved in the regulation of T3 concentrations, especially during the embryonic and early post-natal periods. DIII is expressed in neurons and degrades T4 and T3 to inactive metabolites. The action of T3 is mediated through nuclear receptors, which are expressed mainly in neurons. The receptors are ligand-modulated transcription factors, and a number of genes have been identified as regulated by thyroid hormone in brain. The regulated genes encode proteins of myelin, mitochondria, neurotrophins and their receptors, cytoskeleton, transcription factors, splicing regulators, cell matrix proteins, adhesion molecules, and proteins involved in intracellular signaling pathways. The role of thyroid hormone is to accelerate changes of gene expression that take place during development. Surprisingly, null-mutant mice for the T3 receptors show almost no signs of central nervous system involvement, in contrast with the severe effects of hypothyroidism. The resolution of this paradox is essential to understand the role of thyroid hormone and its receptors in brain development and function.

Growth-restricted premature infants are at increased risk for low thyroxine

OBJECTIVE

To evaluate, in extremely premature infants, the relationship between growth restriction and early total thyroxine levels, and to determine how maternal, prenatal, perinatal and neonatal variables influence the relationship.

STUDY DESIGN

719 infants born at four medical centers in Massachusetts, New York and New Jersey between 1991 and 1993 were studied. Entry criteria included: gestational age 23--30 weeks, birth weight 500--1500 g, and a serum thyroxine level obtained in the first week of life. Infants born to mothers with a history of thyroid disease were excluded. Birth weight and total thyroxine level are expressed as z-scores (standard deviation units) to adjust for their relationship to gestational age.

RESULTS

In linear regression analysis, there was a 0.18 decrease in the total thyroxine z-score for each 1.0 (1 standard deviation unit) decrease in birth weight z-score (p=0.0001). Adjustment for multiple potential maternal, prenatal, perinatal and neonatal confounders failed to identify a factor or factors that could account for the observed association.

CONCLUSIONS

The early total thyroxine level in extremely preterm infants was significantly associated with birth weight z-score. This relationship persisted even after adjustment for maternal, prenatal, perinatal and neonatal confounders suggesting antenatal influences. Of clinical importance, growth-restricted infants are at increased risk for early hypothyroxinemia and, possibly, to its related morbidities.

Thyroid function in very-low-birth-weight infants with intraventricular hemorrhage

The objective of this investigation was to study the natural course of thyroid function in infants with intraventricular hemorrhage (IVH). A cohort of infants < 1,500 grams birth weight, n=247, were included in the analysis. Total T4 and thyrotropin from newborn screening during the 1st week of life (Test 1) and from repeat screening at 2-4 weeks postnatal age (Test 2) were compared in infants with IVH (n=43) and a group of infants without IVH. Fifty-nine percent of infants still had transient hypothyroxinemia at the time of Test 2. After multivariate analysis, infants with IVH had an increased odds of having a T4 < or = 6 microg/dL on Test 1 (OR 2.8, 95% CI 1.2-6.5), but at the time of Test 2 IVH was not associated with an increased odds of having a low T4. Only gestational age (OR 1.6, 95% CI 1.1-2.5) remained associated with an increased odds of having an extremely low T4 (< or = 4 microg/dL) at this time. Transient hypothyroxinemia remains common at 2-4 weeks of age in preterm infants. IVH is not independently associated with having a low T4 at this time.

Thyroid hormone for preventing of neurodevelopmental impairment in preterm infants

BACKGROUND

Observational studies have shown an association between transiently low thyroid hormone levels in preterm infants in the first weeks of life (transient hypothyroxemia) and an abnormal neurodevelopmental outcome. Thyroid hormone therapy might prevent this morbidity.

OBJECTIVES

To assess whether thyroid hormone therapy in preterm infants without congenital hypothyroidism results in clinically important changes in neonatal and long term outcomes in terms of both benefits and harms.

SEARCH STRATEGY

The standard search strategy of the Neonatal Review Group was used. This included searches of the Oxford Database of Perinatal Trials, Cochrane Controlled Trials Register, MEDLINE, previous reviews including cross references, abstracts, conferences, symposia proceedings, expert informants and journal handsearching in the English language.

SELECTION CRITERIA

All trials using random or quasi-random patient allocation, in which thyroid hormone therapy (either treatment or prophylaxis) was compared to a control in premature infants.

DATA COLLECTION AND ANALYSIS

Primary clinical outcomes included measures of neurodevelopmental outcome and mortality. Assessment of trial quality, data extraction and synthesis of data, using relative risk (RR) and weighted mean difference (WMD), were performed using standard methods of the Cochrane Collaboration and its Neonatal Review Group.

MAIN RESULTS

Eight studies were identified that compared thyroid hormone treatment to control. Four randomized or quasi-randomized studies met inclusion criteria (Chowdhry 1984, Amato 1989, van Wassenaer 1997 and Vanhole 1997). All studies enrolled preterm infants < 32 weeks gestation, but used different timing, dose and duration of treatment with thyroid hormones. Three studies used thyroxine, whereas Amato 1989 used triiodothyronine. Only two studies with neurodevelopmental follow-up were of good methodology (van Wassenaer 1997 and Vanhole 1997). All studies were of small size with the largest, van Wassenaer 1997, enrolling 200 infants. A lack of comparability of data (neurodevelopmental test or timing of follow-up) prevented meta-analytic pooling of the studies for neurodevelopmental outcomes. There was no significant difference in mortality to discharge (typical relative risk 0.74, 95% CI 0.44, 1.26) in infants who received thyroid hormone treatment compared to controls. In individual studies, no significant differences were found in neurodevelopmental outcomes including risk of abnormal neurological outcome, and Bayley Mental or Psychomotor Development Indices. No data were available for the incidences of cerebral palsy or sensorineural impairment. Fraction of inspired oxygen was lower in infants receiving triiodothyronine in one small quasi-randomized study (Amato 1989), but not in infants receiving thyroxine in a randomized study (Vanhole 1997). No other differences were found to suggest a reduced severity of respiratory distress syndrome in infants receiving early thyroid hormone therapy.

REVIEWER'S CONCLUSIONS

This review does not support the use of thyroid hormones in preterm infants to reduce neonatal mortality, improve neurodevelopmental outcome or to reduce the severity of respiratory distress syndrome. The a posteriori subgroup analyses of data from one study (van Wassenaer 1997) which showed benefits in infants 24-25 weeks gestation should be treated with caution. The small number of infants included in trials incorporated in this review limits the power of the meta-analysis to detect clinically important differences in neonatal outcomes. Future trials should be of sufficient size to detect clinically important differences in neurodevelopmental outcomes. They should consider enrolling those infants most likely to benefit from thyroid hormone treatment such as infants born at less than 27 weeks gestation and use thyroid hormones as treatment instead of prophylaxis.

Hypothyroxinemia in premature infants: is thyroxine treatment necessary?

The increased survival of very low birth weight (VLBW) premature infants has been associated with an increased prevalence of transient disorders of thyroid function during the early weeks of life. All VLBW infants have relatively low, and gestation age-dependent, thyroxine-binding globulin (TBG) concentrations associated with variably low total thyroxine (T4) concentrations. These infants also have a high prevalence (30%-60%) of nonthyroidal illnesses that impact thyroid function, including total and free iodothyronine concentrations. Finally, thyroid gland hormone biosynthesis and the hypothalamic-pituitary axis are relatively immature and thyroid glandular iodine stores are low. As a result, VLBW infants manifest a high prevalence of transient primary hypothyroidism (0.41%) and transient hypothalamic-pituitary (thyrotropin [TSH] deficiency) hypothyroidism (5%-10%?). Thyroid function should be monitored in VLBW infants during the first 1-4 weeks of life to detect these disorders as well as the much less common permanent congenital hypothyroidism. An elevated serum TSH level (> 20 mU/L) is diagnostic of primary hypothyroidism and a low free T4 concentration with a normal or low serum TSH level suggests hypothalamic-pituitary hypothyroidism. Treatment of transient or permanent primary hypothyroidism and of congenital TSH deficiency is indicated. Preliminary data suggests that 30-60-day treatment of transient hypothalamic-pituitary hypothyroidism improves IQ at 2 years of age. However, further information confirming the benefit of treatment, the threshold free T4 values for diagnosis, and the optimal dose of T4 are necessary.

Diagnosis and management of maternal and fetal thyroid disorders

Thyroid diseases in pregnancy are a group of disorders with different clinical manifestations which require a rational approach in their diagnosis and management. In many cases, this involves a team approach including different specialties. Several topics have received particular attention in recently published reports. The syndrome of transient hyperthyroidism of hyperemesis gravidarum, more frequently recognized and considered to be caused by inappropriate concentrations of human chorionic gonadotropin in plasma, has been reported for the first time to be secondary to a mutation in the thyrotropin-releasing hormone receptor. Mutations in the thyrotropin-releasing hormone receptor have also being found in cases, most of them familiar, of congenital hypothyroidism caused by resistance to thyrotropin-releasing hormone. However, other cases of congenital hypothyroidism with resistance to thyrotropin-releasing hormone were not caused by mutations in the thyrotropin-releasing hormone receptor. This is a fascinating new field in molecular medicine, stimulated by clinical observations in infants born with congenital hypothyroidism that did not fulfill the classical clinical descriptions. New studies in the metabolism and transfer of anti-thyroid drugs from mother to fetus have indicated no differences between propylthiouracil and methimazole. Finally, changes in titers and the biological action of thyrotropin-releasing hormone receptors antibodies appear to explain the clinical observation of improvement in Graves' hyperthyroidism during the second half of pregnancy and its recurrence during the postpartum period.