Thyroid function in asphyxiated newborns who received hypothermia therapy

The Association Between Hypoxic-Ischemic Encephalopathy and Thyroid Hormones

We aimed to compare serum thyroid-stimulating hormone (TSH) and free thyroxine (fT4) levels in neonates with different hypoxic-ischemic encephalopathy (HIE) stages undergoing therapeutic hypothermia (TH), and to evaluate the TSH and fT4 levels in neonates with HIE/TH in comparison with a control group. This was a retrospective study conducted between January 2020 and December 2022. The neonates with HIE/TH constituted the study group and the neonates with transient tachypnea of the newborn (TTN) constituted the control group. The study group consisted of neonates with stage 2 and stage 3 HIE. Serum TSH and fT4 levels measured at postnatal fifth day were compared between the groups. Of the 202 (47.1%) neonates included in the study group, 144 (71.3%) had stage 2 HIE and 58 (28.7%) had stage 3 HIE. In the control group, there were 227 (52.9%) newborns. Serum TSH and fT4 levels were found to be lower in the newborns with stage 3 HIE compared with those with stage 2 HIE (p = 0.015, 0.002, respectively). Although the serum TSH level was higher in the newborns with HIE compared with the newborns with TTN, serum fT4 levels did not change between the groups (p = < 0.001, 0.14, respectively). When we made the analysis according to the reference intervals, HIE/TH was associated with higher rates of TSH elevation compared with TTN, and the difference was more pronounced in stage 2 HIE/TH (p < 0.001). Although stage 3 HIE/TH was significantly associated with higher rates of low fT4 compared with TTN (p = 0.006), this relationship was not significant between stage 2 HIE/TH and TTN. It would be reasonable to interpret thyroid function tests performed on the fifth day with caution in newborns with HIE/TH, because higher TSH and lower fT4 levels on the fifth day in this patient group may result in unnecessary repetition of tests.

Perinatal asphyxia and hypothermic treatment from the endocrine perspective

Introduction

Perinatal asphyxia is one of the three most important causes of neonatal mortality and morbidity. Therapeutic hypothermia represents the standard treatment for infants with moderate-severe perinatal asphyxia, resulting in reduction in the mortality and major neurodevelopmental disability. So far, data in the literature focusing on the endocrine aspects of both asphyxia and hypothermia treatment at birth are scanty, and many aspects are still debated. Aim of this narrative review is to summarize the current knowledge regarding the short- and long-term effects of perinatal asphyxia and of hypothermia treatment on the endocrine system, thus providing suggestions for improving the management of asphyxiated children.

Results

Involvement of the endocrine system (especially glucose and electrolyte disturbances, adrenal hemorrhage, non-thyroidal illness syndrome) can occur in a variable percentage of subjects with perinatal asphyxia, potentially affecting mortality as well as neurological outcome. Hypothermia may also affect endocrine homeostasis, leading to a decreased incidence of hypocalcemia and an increased risk of dilutional hyponatremia and hypercalcemia.

Conclusions

Metabolic abnormalities in the context of perinatal asphyxia are important modifiable factors that may be associated with a worse outcome. Therefore, clinicians should be aware of the possible occurrence of endocrine complication, in order to establish appropriate screening protocols and allow timely treatment.

Thyroid Function in Neonates with Hypoxic Ischemic Encephalopathy

We aimed to examine heel prick (capillary) and serum thyroid function test (TFT) results in neonates with hypoxic ischemic encephalopathy (HIE) to evaluate the effect of asphyxia and therapeutic hypothermia (TH) on thyroid functions. This retrospective chart review included infants who were born after 34 weeks of gestation, were diagnosed and treated for HIE. The patients were divided into those who did and did not undergo TH and the groups were compared in terms of demographic characteristics, laboratory results, capillary thyroid-stimulating hormone (cTSH) levels, and serum thyroid-stimulating hormone (TSH) and free thyroxine (fT4) levels. A total of 111 neonates were included in the study. There was no difference between the TH group (n = 90) and the nonhypothermia group (n = 21) in terms of median gestational age (38.3 ± 2.1 weeks vs. 38.6 ± 1.8 weeks, p = 0.42) or birth weight (3182 ± 509 g vs. 3174 ± 573 g, p = 0.72). Serum TFT was performed at a median of 10 days (range, 2-43) and capillary TSH analyzed at a median of 6 days (range, 1-26). Capillary TSH at 96 hours was analyzed in 36 patients in the TH group and 19 patients in the nonhypothermia group. Serum TSH and fT4 levels were similar in both groups (p = 0.29, p = 0.1). Overall cTSH and cTSH obtained in the first 4 days were 2.2 (0.5-10) and 4.3 (0.5-94), p = 0.059; 2 (0.5-22) and 5 (0.5-94), p = 0.04, respectively, whereas cTSH obtained after day 4 was similar in both groups (p = 0.058). Abnormal serum TSH (>5.5 mU/mL) was more frequent in the hypothermia group (44.4% vs. 19%, p = 0.026). Our results suggest that TH may cause some alterations on TFTs. Therefore, it may be reasonable to repeat TSH screening after TH.

Congenital Hypothyroidism in Preterm Newborns - The Challenges of Diagnostics and Treatment: A Review

Preterm newborns are forced to adapt to harsh extrauterine conditions and endure numerous adversities despite their incomplete growth and maturity. The inadequate thyroid hormones secretion as well as the impaired regulation of hypothalamus-pituitary-thyroid axis may lead to hypothyroxinemia. Two first weeks after birth are pivotal for brain neurons development, synaptogenesis and gliogenesis. The decreased level of thyroxine regardless of cause may lead to delayed mental development. Congenital hypothyroidism (CH) is a disorder highly prevalent in premature neonates and it originates from maternal factors, perinatal and labor complications, genetic abnormalities, thyroid malformations as well as side effects of medications and therapeutic actions. Because of that, the prevention is not fully attainable. CH manifests clinically in a few distinctive forms: primary, permanent or transient, and secondary. Their etiologies and implications bear little resemblance. Therefore, the exact diagnosis and differentiation between the subtypes of CH are crucial in order to plan an effective treatment. Hypothyroxinemia of prematurity indicates dynamic changes in thyroid hormone levels dependent on neonatal postmenstrual age, which directly affects patient's maintenance and wellbeing. The basis of a successful treatment relies on an early and accurate diagnosis. Neonatal screening is a recommended method of detecting CH in preterm newborns. The preferred approach involves testing serum TSH and fT4 concentrations and assessing their levels according to the cut-off values. The possible benefits also include the evaluation of CH subtype. Nevertheless, the reference range of thyroid hormones varies all around the world and impedes the introduction of universal testing recommendations. Unification of the methodology in neonatal screening would be advantageous for prevention and management of CH. Current guidelines recommend levothyroxine treatment of CH in preterm infants only when the diagnose is confirmed. Moreover, they underline the importance of the re-evaluation among preterm born infants due to the frequency of transient forms of hypothyroidism. However, results from multiple clinical trials are mixed and depend on the newborn's gestational age at birth. Some benefits of treatment are seen especially in the preterm infants born <29 weeks' gestation. The discrepancies among trials and guidelines create an urgent need to conduct more large sample size studies that could provide further analyses and consensus. This review summarizes the current state of knowledge on congenital hypothyroidism in preterm infants. We discuss screening and treatment options and demonstrate present challenges and controversies.

An analysis of perinatal factors of low T3 syndrome in preterm neonates with a gestational age of 28-35 weeks

OBJECTIVE

Low triiodothyronine syndrome (LT3S) is a common endocrine disease in preterm neonates. Various serious acute or chronic diseases result in LT3S. Few studies have investigated the causal relationship between perinatal factors and LT3S in preterm neonates with a gestational age (GA) of 28-35 weeks. The present study comprehensively analyzed the perinatal factors of LT3S in preterm neonates.

METHODS

This was a retrospective study of neonates with and without LT3S from January 2018 to November 2019. Compared to 206 preterm neonates without LT3S, 158 neonates were diagnosed with LT3S, excluding neonates with congenital malformations, other endocrine diseases, genetic diseases and inherited metabolic diseases.

RESULTS

Five perinatal risk factors for LT3S were confirmed using univariate and multivariate analyses: smaller gestational age, lower birth weight, respiratory distress syndrome (RDS), neonatal sepsis, and dopamine use.

CONCLUSIONS

LT3S in preterm neonates was associated with multiple perinatal factors, including smaller gestational age, lower birth weight, RDS, sepsis, and dopamine use. Preterm neonates with a GA of 28-35 weeks who are exposed to a series of high-risk perinatal factors must be closely observed, diagnosed early and treated for primary diseases promptly to reduce the occurrence of LT3S and improve the outcomes.Key Message:Few studies have investigated the relationship between perinatal factors and Low triiodothyronine syndrome (LT3S) in preterm neonates with a gestational age (GA) of 28-35 weeks.LT3S was associated with multiple perinatal factors, including smaller gestational age, lower birth weight, respiratory distress syndrome (RDS), sepsis, and dopamine use.