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

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.

Hypothyroxinemia and weight velocity in preterm infants

OBJECTIVES

Hypothyroxinemia of prematurity (HOP) is characterized by low free thyroxine (FT4) associated with low or normal thyroid stimulating hormone (TSH). The objective of this study is to define FT4 and TSH values in very preterm infants (<32 weeks postmenstrual age, PMA) and correlate hypothyroxinemia and levothyroxine treatment with growth velocity at 28 days and 36 weeks PMA.

METHODS

Preterm neonates <32 weeks PMA admitted to the regional neonatal intensive care unit (NICU) at the Children's Hospital of Georgia (USA) between January 2010 and July 2022 were routinely screened for hypothyroxinemia. FT4 and TSH values were obtained on 589 eligible neonates between day of life (DOL) 4 and 14. Growth velocity (g/kg/day) from DOL 14 to DOL 28 and 36-weeks PMA were calculated for each neonate and potential explanatory variables (PMA, sex, and race) were incorporated into multivariate regression models to identify associations between HOP and growth velocity.

RESULTS

In 589 preterm infants, PMA at birth was strongly associated inversely with FT4 (R=0.5845) and modestly with TSH (R=0.2740). Both FT4 and gestational age, but not TSH or levothyroxine treatment, were associated with growth velocity at 28 days of life and at 36 weeks PMA.

CONCLUSIONS

We provide a large data set for identifying FT4 and TSH measurements and identify hypothyroxinemia of prematurity as a potential mediator of slow postnatal growth in very preterm infants.

Neurodevelopmental Outcome of Infants with Transient Hypothyroxinemia of Prematurity in a Newborn Intensive Care Unit

Objective

The aim of this study was to evaluate neurological development of infants with transient premature hypothyroxinemia (THOP).

Methods

This prospective study included newborns who were born between 28-36 weeks of gestation (GW) and were admitted to the neonatal intensive care unit. Newborns exposed to maternal thyroid disease, or with severe intracranial problems, and congenital anomalies were excluded. Infants with THOP were the study group and those without THOP formed the control group. The study group was subdivided into those receiving levothyroxine replacement (5 μg/kg/day) and those who were untreated. Neonatal demographics, and morbidities, including respiratory distress syndrome, bronchopulmonary dysplasia (BPD) and retinopathy of prematurity (ROP) were evaluated. The Ages and Stages Questionnaire (ASQ) and ASQ:Social-Emotional (ASQ:SE) developmental screening tests were administered to the entire study population at the corrected age of two years.

Results

Seventy infants were included in this study, 40 of whom had THOP. The mean GW was 34.4±3.8 weeks in the study group and 37.2±2.3 weeks in controls (p=0.69). Mean overall birth weight was 1640±428 g. Levothyroxine replacement was started in 12/40 infants (30%). The groups were similar in terms of demographic characteristics. Rates of BPD and ROP were higher in the treated group (p=0.01). ASQ and ASQ:SE results did not differ between groups (p=0.75), nor did these scores differ between infants with THOP who did or did not receive levothyroxine (p=0.14).

Conclusion

Although levothyroxine replacement therapy was associated with increased rates of BPD and ROP, this treatment did not appear to improve long-term neurological outcomes in this small group of infants with THOP. Prospective controlled studies with much larger sample sizes are needed to clarify the role of levothyroxine replacement in THOP.

Clinical indicators that influence a clinician's decision to start L-thyroxine treatment in prematurity with transient hypothyroxinemia

BACKGROUND

Transient hypothyroxinemia of prematurity (THOP) is defined as a low level of circulating thyroxine (T4), despite low or normal thyroid-stimulating hormone (TSH) levels.

AIMS

We aimed to evaluate the incidence of THOP, the clinical and laboratory findings of preterm infants with this condition and the levothyroxine (L-T4) treatment.

METHODS

Preterm infants (n = 181) delivered at 24-34 weeks of gestation were evaluated by their thyroid function tests that were performed between the 10th and 20th days of postnatal life and interpreted according to the gestational age (GA) references. Clinical and laboratory characteristics of the patients with THOP and normal thyroid function tests were compared. Patients with THOP and treated with L-T4 were compared with the ones who were not regarding laboratory, and clinical characteristics.

RESULTS

Incidence of hypothyroxinemia of prematurity was 45.8% (n = 83). Euthyroidism, primary hypothyroidism, and subclinical hypothyroidism were diagnosed in 47.5% (n = 86), 5% (n = 9) and 1.7% (n = 3) of the patients, respectively. Mean birth weight (BW) and GA were significantly lower in the hypothyroxinemia group than in the euthyroid group (p < 0.001). L-T4 was started in 43% (n = 36) of the patients with THOP. Treatment initiation rate was 44.4% (n = 16) in 24-27 wk, 41.6% (n = 15) in 28-30 wk, and 13.8% (n = 5) in 31-34 wk. As the GA increased, the incidence of THOP and the rate of treatment initiation decreased (p < 0.001). The lowest free thyroxine (FT4) cut-off value was 0.72 ng/dl in the treated group. In addition, incidences of vancomycin + amikacin, caffeine, dopamine treatments, RDS, IVH, BPD, central catheter, FFP transfusion, and ventilator support were higher in the treated group (P < 0.05).

CONCLUSION

This study revealed that prevalence of THOP increased as the GA and BW decreased. As the GA decreased, THOP patients requiring L-T4 treatment increased. Additionally, association with comorbid diseases increased the requirement of treatment.

The effects of topical iodine containing antiseptics on thyroidal status and early neurodevelopment of preterm infants

OBJECTIVES

The goal of this study was to determine the quality of these disinfectants' effects on thyroid function and neurological scores in premature newborns aged 28 to 36 gestational weeks (GW).

METHODS

This cohort study was conducted from October 2020 to September 2021 among 28-36 GW preterm infants at the neonatal care unit of Jiangnan University Hospital. We divided this 12 month period into two consecutive 6 month periods. Composite iodine disinfectants and alcohol are used for skin and umbilical cord disinfection of preterm infants, respectively. Urinary iodine concentration (UIC), thyroid hormone levels, and neonatal behavioral and neurological assessment (NBNA) scores were determined in both groups.

RESULTS

A total of 126 patients were included in the study, 65 in the iodine exposed group and 61 in the alcohol group. The second UIC and the incidence of serum T4≤5 μg/dL and TSH≥10 mIU/L in the iodine exposed group were significantly higher than those in the alcohol group (p<0.05). The first NBNA score was lower in the iodine exposed group than in the alcohol group (p<0.05). However, whether it has clinical significance remains to be explored. There was a linear relationship between the two NBNA scores (iodine exposure group, R ²=0.344; alcohol group, R ²=0.227). No sepsis or other adverse outcomes occurred in the two groups of preterm infants after disinfection with different disinfectants.

CONCLUSIONS

Iodine-containing disinfectants seem to have the potential to cause an increased rate of thyroid dysfunction and a decreased neurological score and should be evaluated in further studies.

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.

The factors associated with transient hypothyroxinemia of prematurity

Background

Hypothyroxinemia is defined by low levels of thyroxine (T4) despite low or normal levels of thyroid-stimulating hormone (TSH). This study aimed to evaluate the factors associated with transient hypothyroxinemia of prematurity (THOP) in newborns admitted to the neonatal intensive care unit (NICU).

Method

This is a single center, retrospective, case-control study. Premature newborns, between 24 and 34 weeks of gestation, hospitalised between January 2014–December 2019 in Istanbul University-Cerrahpasa Faculty of Medicine NICU were analyzed through their medical records. Thyroid function tests were routinely performed between the 10th and 20th days of postnatal life and were evaluated according to the gestational age references. Thirty six possible associated factors (prenatal and postnatal parameters, medical treatments, clinical diagnoses and applications in NICU) were searched in the patient group with THOP (n = 71) and the control group with euthyroid prematures (n = 73). The factors for THOP were identified by univariate analysis, followed by multivariate analysis.

Results

Mean gestational ages of the study and the control groups were 29.7 ± 2.48 and 30.5 ± 2.30 weeks, respectively (p = 0.606). The birth weight, small for gestational age (SGA), intraventricular hemorrhage (IVH), congenital heart disease (CHD) were found to be the possible associated factors for THOP in the univariate analysis and CHD (p = 0.007, odds ratio [OR]:4.9, 95% confidence interval [CI]: 1.5–15.8), BW (p = 0.004, OR:0.999, 95% CI: 0.9–1.0) and SGA (p = 0.010, OR:4.6, 95% CI: 1.4–14.7) were found to be factors associated with THOP determined by univariate logistic regression analysis.

Conclusıons

Although some treatment practices might have had direct effects on pituitary–thyroid axis, related with the severity of the newborn clinical conditions, non of them was found to be a associated factor for THOP. However, CHD and SGA may be considered as associated factors with THOP detected in preterm infants.

Transient hypothyroxinemia of prematurity and its risk factors in an extramural neonatal intensive care unit

Objective

Thyroid functions in preterm newborns may be altered in the first week of life. Hypothyroxinemia has been commonly reported in these babies, which could be due to the immaturity of the hypothalamic pituitary thyroid axis or acute illness. It could have a long-term impact on the developing brain of these babies. We conducted this study to estimate the incidence of transient hypothyroxinemia of prematurity (THOP) and to determine its risk factors.

Methods

We analyzed thyroid stimulating hormone (TSH) and free T4 levels of 64 preterm neonates admitted in the neonatal intensive care unit. TSH and free T4 levels were measured in the first week and then at 14-21 days of life to estimate the incidence of THOP and determine its risk factors. We also estimated the incidence of congenital hypothyroidism (CH) and delayed TSH elevation in CH. Risk analysis was conducted using simple and multiple logistic regression, and numerical data was compared using the Mann Whitney U test and t test.

Results

THOP was seen in 25% of the preterm babies. Caesarean delivery, presence of one or more morbidities, mechanical ventilation, birth weight ≥ 1,500 g, and gestational age ≥ 32 weeks were identified as risk factors for THOP based on simple logistic regression. In multiple regression, mechanical ventilation and gestational age ≥ 32 weeks were significantly associated with THOP. CH was seen in 2 (3.1%) babies, and 1 of these cases had delayed TSH elevation.

Conclusion

Thyroid abnormalities are common in preterm admitted neonates. Mechanical ventilation is an independent risk factor for development of THOP.

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 Preterm/Low Birth Weight Infants: Impact on Diagnosis and Management of Thyroid Dysfunction

Maternal thyroid hormone crosses the placenta to the fetus beginning in the first trimester, likely playing an important role in fetal development. The fetal thyroid gland begins to produce thyroid hormone in the second trimester, with fetal serum T4 levels gradually rising to term. Full maturation of the hypothalamic-pituitary-thyroid (HPT) axis does not occur until term gestation or the early neonatal period. Postnatal thyroid function in preterm babies is qualitatively similar to term infants, but the TSH surge is reduced, with a corresponding decrease in the rise in T4 and T3 levels. Serum T4 levels are reduced in proportion to the degree of prematurity, representing both loss of the maternal contribution and immaturity of the HPT axis. Other factors, such as neonatal drugs, e.g., dopamine, and non-thyroidal illness syndrome (NTIS) related to co-morbidities contribute to the "hypothyroxinemia of prematurity". Iodine, both deficiency and excess, may impact thyroid function in infants born preterm. Overall, the incidence of permanent congenital hypothyroidism in preterm infants appears to be similar to term infants. However, in newborn screening (NBS) that employ a total T4-reflex TSH test approach, a higher proportion of preterm babies will have a T4 below the cutoff, associated with a non-elevated TSH level. In NBS programs with a primary TSH test combined with serial testing, there is a relatively high incidence of "delayed TSH elevation" in preterm neonates. On follow-up, the majority of these cases have transient hypothyroidism. Preterm/LBW infants have many clinical manifestations that might be ascribed to hypothyroidism. The question then arises whether the hypothyroxinemia of prematurity, with thyroid function tests compatible with either non-thyroidal illness syndrome or central hypothyroidism, is a physiologic or pathologic process. In particular, does hypothyroxinemia contribute to the neurodevelopmental impairment common to preterm infants? Results from multiple studies are mixed, with some randomized controlled trials in the most preterm infants born <28 weeks gestation appearing to show benefit. This review will summarize fetal and neonatal thyroid physiology, thyroid disorders specific to preterm/LBW infants and their impact on NBS for congenital hypothyroidism, examine treatment studies, and finish with comments on unresolved questions and areas of controversy.

Hyperoxia Leads to Transient Endocrine Alterations in the Neonatal Rat During Postnatal Development

Introduction: High oxygen concentrations have been identified as one factor contributing to the pathogenesis of the retinopathia of prematurity, chronic lung disease of the preterm infant and preterm brain injury. Preterm infants also show short- and long-term alterations of the endocrine system. If hyperoxia is one pathogenetic factor has not been investigated yet. With regard to the high prevalence of neurodevelopmental impairments in preterm infants, the hypothalamus-pituitary-thyroid (HPT) axis, the hypothalamus-pituitary-adrenal (HPA) axis and the hypothalamus-pituitary-somatotropic (HPS) axis are of special interest due to their important role in neurodevelopment. Objective: The aim of this study was to investigate the effect of hyperoxia on the endocrine system in the neonatal rat by analyzing the activities of the HPT, HPA and HPS axes, respectively. Methods: Three-days old Wistar rats were exposed to hyperoxia (oxygen 80%, 48 h). On postnatal day 5 (P5) and P11, transcript levels of thyroid-stimulating hormone (TSH), proopiomelanocortin and growth hormone (GH) were analyzed in pituitary sections by in situ hybridization. Serologic quantification of TSH and thyroxine (T4), adrenocorticotropic hormone and GH were performed by Multiplex analysis and Enzyme-linked Immunosorbent Assay. Results: At P5, significantly lower GH levels were observed in pituitaries (mRNA) and in sera of rats exposed to hyperoxia. Serum TSH was significantly elevated without changes in T4. Conclusion: This is the first study demonstrating transient endocrine alterations following hyperoxia in the neonatal rat making oxygen a possible contributor to the pathogenesis of endocrine alterations seen in preterm infants. Considering the detrimental multi-organ effects of hyperoxia on the immature organism, a rational use of therapeutic oxygen in the treatrnent of preterm infants is of utmost importance.

[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.