Effect of L-thyroxine supplementation on very low birth weight infants with transient hypothyroxinemia of prematurity at 3 years of age

A practical gestational age-based algorithm for timely detection of hypothyroidism in premature infants

OBJECTIVES

To assess utility and accuracy of a gestational age-based screening targeting premature infants to detect congenital hypothyroidism.

STUDY DESIGN

A prospective cohort study was conducted in infants <35 weeks' gestational age with clinical outcomes at 2-3 years of age. Patients received newborn screenings at 24 hours and 10-14 days of life. Free T4 (FT4) and thyroid-stimulating hormone (TSH) levels were measured at one month of life and repeated based on algorithm by corrected gestational age.

RESULTS

Among infants <35 weeks gestation (n = 938), the incidence of hypothyroidism requiring treatment was 1:58. TSH levels at one month of age was predictive of treatment (AUC 0.96, 95% CI 0.88-1). The optimal TSH threshold of 8 mIU/L (8 µU/ml) increased the specificity to 0.97 and sensitivity to 0.88. Following initiation of treatment for hypothyroidism during NICU hospitalization, 43.8% (n = 7) were diagnosed with permanent congenital hypothyroidism.

CONCLUSIONS

Our study supports a gestational age-based screening algorithm for early detection of hypothyroidism in premature infants.

Developmental Trends in Postnatal Thyroid Hormones and Thyroid Dysfunction in Preterm Infants Born at less than 34 weeks Gestation

OBJECTIVES

To analyse the trends in thyroid function tests (TFT) in preterm infants, evaluate the frequency of thyroid dysfunction, and identify the factors that influence thyroid function.

METHODS

The TFT results and risk factors for thyroid dysfunction in preterm infants with gestational ages (GA) between 25 and 34 weeks were analysed.

RESULTS

In total, 535 infants were enrolled in this study. Thyroid hormone levels vary with gestational and postnatal age, and the total frequency of thyroid dysfunction is 50.3%. Thirty-one infants (5.8%) had delayed TSH elevation. Transient hypothyroxinaemia of prematurity remained significantly associated with both lower birth weight and GA. Congenital hypothyroidism was significantly associated with lower birth weight, 5 min Apgar score, and dopamine use.

CONCLUSIONS

Thyroid hormone levels in preterm infants are related to gestation and postnatal age, the frequency of thyroid dysfunction in premature infants is high, and is negatively correlated with GA and birth weight.

Postnatal Serum Total Thyroxine Level Associated with Short- and Long-Term Anthropometric Outcomes in Very Preterm Infants

Thyroxine (T4) importantly regulates the growth of newborns. Compared to fetuses with equivalent gestational ages, very preterm infants (VPIs) often experience relatively low thyroxinemia, with a normal thyroid-stimulating hormone (TSH) concentration < 10 μIU/mL. However, there is continued debate regarding postnatal thyroxine supplementation for VPIs with normal TSH and transitionally low thyroxinemia. Little research has explored the role of the postnatal total T4 (TT4) serum concentration on the growth of VPIs. In this study, we aim to clarify whether the postnatal thyroxine concentration is associated with the short- and long-term growth outcomes of VPIs. A total of 334 surviving VPIs in our previously reported cohort, born in the period August 2007−July 2016, were enrolled. The exposure variable was the postnatal TT4 concentration at 1 month old. The primary outcomes were body weight increments over 28 days after the screening and anthropometric outcomes at the corrected age of 24 months old. Infants with any hormonal replacement, severe brain injury, congenital anomaly, or cerebral palsy were excluded. In total, 290 (86.8%) VPIs were included for analysis. In the 28 days after thyroid function screening, the TT4 concentration was found to have a significant association with positive increments in body weight (mean increment: 25.7 g per 1 μg/dL; p < 0.001) and a positive body weight z-score (mean increment: 0.039 per 1 μg/dL; p = 0.037), determined by generalized estimating equation analysis. At the corrected age of 24 months old, a higher postnatal TT4 concentration was associated with a lower body mass index (mean coefficient: −0.136; 95% CI: −0.231 to −0.041, p = 0.005) and lower body mass index z-score (mean coefficient: −0.097; 95% CI: −0.170 to −0.024, p = 0.009). Infants with a TT4 concentration > 6.4 ug/dL had significantly lower odds of overweight status (odds ratio: 0.365; 95% CI: 0.177 to 0.754, p = 0.006). We conclude that the postnatal TT4 concentration is associated with a positive increment in body weight in the short term. At the same time, the postnatal TT4 concentration is associated with lower odds of overweight status after long-term follow-up.

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.

Guideline for the Treatment of Hypothyroidism in Prematurity

Congenital hypothyroidism is one of the most common endocrine disorders in infants and children. Thyroid hormone effects the function of most organs of the body. In premature neonates, thyroid abnormalities are very common but transient. There is a significant difference between the appropriate time for screening in premature and term neonates and there are different viewpoints in treating hypothyroidism in prematurity. According to the probable exceptions in this issue, there is no definite guideline. Therefore, regarding this confusion, this guideline aimed to help clinicians for rapid on-time decision making.

Postnatal Serum Total Thyroxine of Very Preterm Infants and Long-Term Neurodevelopmental Outcome

Primary congenital hypothyroidism is a disease associated with low serum thyroxine and elevated thyroid-stimulating hormone (TSH) levels. The processes of screening and treating congenital hypothyroidism, in order to prevent neurodevelopmental impairment (NDI) in newborns, have been well investigated. Unlike term infants, very preterm infants (VPIs) may experience low thyroxine with normal TSH levels (<10.0 μIU/mL) during long-stay hospitalization. In the current literature, thyroxine treatment has been evaluated only for TSH-elevated VPIs. However, the long-term impact of low thyroxine levels in certain VPIs with normal TSH levels deserves more research. Since July 2007, VPIs of this study unit received screenings at 1 month postnatal age (PNA) for serum TSH levels and total thyroxine (TT4), in addition to two national TSH screenings scheduled at 3–5 days PNA and at term equivalent age. This study aimed to establish the correlation between postnatal 1-month-old TT4 concentration and long-term NDI at 24 months corrected age among VPIs with serial normal TSH levels. VPIs born in August 2007–July 2016 were enrolled. Perinatal demography, hospitalization morbidities, and thyroid function profiles were analyzed, and we excluded those with congenital anomalies, brain injuries, elevated TSH levels, or a history of thyroxine treatments. In total, 334 VPIs were analyzed and 302 (90.4%) VPIs were followed-up. The postnatal TT4 concentration was not associated with NDI after multivariate adjustment (odd ratios 1.131, 95% confidence interval 0.969–1.32). To attribute the NDI of TSH-normal VPIs to a single postnatal TT4 concentration measurement may require more research.

[Thyroid function in < 32 weeks gestation preterm infants]

INTRODUCTION

Preterm newborns (PN) have a higher risk of thyroid dysfunction than term newborns (TN). This condition may go unnoticed in neonatal screening due to a late elevation of thyrotropin (TSH) in these patients.

OBJECTIVE

Evaluate thyroid function in the second week of life in PN of < 32 weeks gestation (WG), and to identify factors associated to its alteration.

PATIENTS AND METHODS

A retrospective study was performed in neonates of < 32 weeks gestation (WG), in whom thyroid function was determined. An analysis was performed on thyroxine (T4L) and TSH levels, as well as their association with perinatal and neonatal outcomes.

RESULTS

The study included a total of 358 patients with mean gestational age (GA) of 29.3 weeks, and mean birth weight (BW) 1127 grams. A linear correlation was found between T4L and BW (correlation coefficient (R) 0.356; p < 0.001) and GA (R = 0.442; p < 0.001). TSH values were associated with small for gestational age (SGA 5.3 mU/L [1.5-37]; non-SGA 2.89 mU/L [0.2-19.5]; p < 0.001), inotropic support (Yes 3.98 mU/L [0.6-22.9]; No 3.16 mU/L [0.2-37]; p = 0.019) and BW (R = -0.249; p < 0.001). Nine (2.5%) patients were treated with levothyroxine, of whom six were SGA.

CONCLUSIONS

Thyroid function analysis in the second week of life helps to identify asymptomatic newborns with risk of thyroid dysfunction. SGA newborns are at higher risk of thyroid function alterations.

Nonthyroidal Illness Syndrome Across the Ages

In conditions of acute illness, patients present with reduced plasma T3 concentrations without a concomitant rise in TSH. In contrast, plasma concentrations of the inactive hormone rT3 increase, whereas plasma concentrations of T4 remain low-normal. This constellation of changes, referred to as nonthyroidal illness syndrome (NTIS), is present across all ages, from preterm neonates and over-term critically ill infants and children to critically ill adults. Although the severity of illness strongly correlates with the severity of the NTIS phenotype, the causality of this association remains debated, and pathophysiological mechanisms remain incompletely understood. In the acute phase of illness, NTIS appears to be caused predominantly by an increased peripheral inactivation of thyroid hormones, in which reduced nutritional intake plays a role. Current evidence suggests that these acute peripheral changes are part of a beneficial adaptation of the body to reduce expenditure of energy and to activate the innate immune response, which is important for survival. In contrast, in more severely ill and prolonged critically ill patients, an additional central suppression of the thyroid hormone axis alters and further aggravates the NTIS phenotype. Recent studies suggest that this central suppression may not be adaptive. Whether treatment of this central component of NTIS in prolonged critically ill patients, with the use of hypothalamic releasing factors, improves outcome remains to be investigated in large randomized control trials.

Review shows that thyroid hormone substitution could benefit transient hypothyroxinaemia of prematurity but treatment strategies need to be clarified

AIM

Thyroid hormones are crucial for foetal and neonatal brain development. This paper provides an overview of the normal role of thyroid hormones in foetal brain development and the pathophysiology of transient hypothyroxinaemia of prematurity (THOP). It also discusses the diagnostic and therapeutic controversies around THOP and looks at directions for future research.

METHODS

We used the PubMed and Embase databases to identify papers published in English from 1969 to June 2018. This identified 20 papers about the impact of THOP on neurodevelopment and seven randomised controlled trials about therapeutic approaches from 1981-2016.

RESULTS

THOP has been researched for more than three decades. The impact of temporarily low thyroxine levels, without any increase in pituitary-secreted thyroid-stimulating hormone at a critical timeframe in an infant's brain development, is still debated. Heterogeneity in THOP definitions, difficulties with thyroid hormone assessment, identifying patients at risk and a clear lack of sufficiently powered studies add to the current controversy. There are indications that thyroid hormone substitution might be useful in extremely low gestational age neonates with THOP.

CONCLUSION

Some preterm infants could benefit from THOP treatment, but more studies are needed to clarify further treatment strategies, including the optimal timing of initiation and duration.

Mild Hypothyroidism in Childhood: Who, When, and How Should Be Treated?

Mild hypothyroidism, also known as subclinical hypothyroidism (SH), is biochemically defined as serum TSH levels above the upper limit of the reference range, in the presence of normal serum concentrations of total T4 and free T4 (FT4). In the neonatal period, mild hypothyroidism can be defined by the presence of a TSH value between 6 and 20 mIU/L and normal FT4 levels. After the neonatal period, SH can be defined mild if TSH ranges between 4.5 and 10 mIU/L. The management of mild hypothyroidism in childhood is challenging. The major concern is to establish whether this condition should always be considered an expression of mild thyroid dysfunction. Indeed, the effects of untreated mild hypothyroidism are still not completely defined. In the neonatal period, concern exists about neurocognitive outcome; in children, although there is no clear evidence of alterations in growth or neurocognitive development, subtle cardiovascular abnormalities have been documented. Therefore, there is still uncertainty about the need of treatment across all ages, and the management should be based on the age of the child, the etiology, and the degree of TSH elevation, as well as on other patient factors. This review updates current evidences on diagnosis and management of mild hypothyroidism in childhood.

Thyroid Function in the Neonatal Intensive Care Unit

Patients in the neonatal intensive care unit (NICU) are at high risk for abnormal thyroid function testing because of illness and preterm birth. Preterm infants are born before hypothalamic-pituitary-thyroid axis maturation and the normal feedback mechanisms that regulate thyroid hormone production remain immature. Preterm and sick infants may develop hypothyroidism even if routine thyroid screening tests collected in the first several days after birth are normal. This article reviews normal hypothalamic-pituitary-thyroid axis maturation, thyroid hormone testing and interpretation in the NICU, and the current evidence for and against levothyroxine treatment of NICU patients with borderline abnormal thyroid function testing.

Current knowledge of transient hypothyroxinemia of prematurity: to treat or not to treat?

BACKGROUND

Thyroid hormones (THs) play a critical role in normal maturation of the developing brain in the fetus and infant. Continuing advances in neonatal medicine have contributed to an increased survival of extremely premature infants with neonatal morbidities. In these infants, thyroid system immaturities, as well as morbidity-related thyroid dysfunction, contribute to transient hypothyroxinemia of prematurity (THOP), which is characterized by very low total and free thyroxine and normal or low thyroid-stimulating hormone (TSH) levels.

REVIEW

Undoubtedly, low levels of THs with elevated TSH are associated with poor neurodevelopmental outcome. However, continuing debate exists regarding whether THOP is harmful to the developing brain. Moreover, no clear effects of TH treatment on neurodevelopmental outcome in preterm infants with THOP have been demonstrated. THs could have unpredictable effects if given unnecessarily.

CONCLUSION

The current recommendation is to treat THOP with TH only if THOP is accompanied with TSH elevation.

Transient hypothyroidism in the newborn: to treat or not to treat

Transient congenital hypothyroidism (CH) refers to a temporary deficiency of thyroid hormone identified after birth, with low thyroxine (T4) and elevated thyrotropin (TSH), which later recovers to improved thyroxine production, typically in first few months of infancy. Approximately 17% to 40% of children diagnosed with CH by newborn screening (NBS) programs were later determined to have transient hypothyroidism. Causes of transient CH are prematurity, iodine deficiency, maternal thyrotropin receptor blocking antibodies, maternal intake of anti-thyroid drugs, maternal or neonatal iodine exposure, loss of function mutations and hepatic hemangiomas. The classic clinical symptoms and signs of CH are usually absent immediately after birth in vast majority of infants due to temporary protection from maternal thyroxine. NBS has been largely successful in preventing intellectual disability by early detection of CH by performing thyroid function tests in infants with abnormal screening results. In this review we present the evidence for decision making regarding treatment vs. withholding treatment in infants with transient CH and present a rational approach to identifying transient CH based on American Academy of Pediatrics (AAP) recommendation.