Congenital hypothyroidism with delayed TSH elevation in low-birth-weight infants: incidence, diagnosis and management

Evaluation of the Congenital Hypothyroidism Detection Strategy in Extremely Preterm Infants in Western Andalusia

OBJECTIVE

This study aimed to identify extremely premature infants (< 31 weeks of gestation and/or <1,500 g) affected by congenital hypothyroidism (CH) with delayed elevation of thyrotropin (TSH) and to evaluate the detection strategy for this pathology in our reference screening population.

STUDY DESIGN

A descriptive and retrospective study was carried out with samples collected from western Andalusia and the autonomous city of Ceuta.

RESULTS

This protocol allowed us to detect six neonates with delayed TSH elevation. One of them, due to serious heart problems, died without being able to confirm CH. In two neonates, however, it was possible to detect CH, another two presented a persistent TSH elevation but normal free T4, and another one presented a temporary TSH elevation.

CONCLUSION

It is essential to repeat the CH screening in extremely premature infants, not only at the age of 15 days but also with a third sample at the moment of hospital discharge to detect cases with delayed TSH elevation.

KEY POINTS

· The Newborn Screening Programs are an essential activity of preventive medicine.. · Extremely preterm infants have a very high risk of CH.. · Optimal management of thyroid dysfunction in this population remains to be established..

Dynamic Screening of Thyroid Function for the Timely Diagnosis of Congenital Hypothyroidism in Very Preterm Infants: A Prospective Multicenter Cohort Study

Background: Preterm infants presented a high prevalence of congenital hypothyroidism (CH), while the optimal screening pattern is still under debate. This study aimed at evaluating the characteristics of thyroid function by conducting weekly screening during the first month of life in very preterm infants (VPIs) to achieve timely diagnosis and treatment of CH. Methods: A prospective cohort study was carried out on VPIs born with gestational age (GA) <32 weeks (w) and admitted to the participating institutes from January 1, 2019 to December 31, 2022. Serial serum thyroid hormone levels were measured weekly within the first month after birth, and at 36 w of corrected age, or before discharge. Datasets for serial thyroid hormone levels and general information were obtained. Results: A total of 5992 VPIs were enrolled in this study, of which 456 (7.6%) [95% confidence interval (CI), 6.9-8.3%] were diagnosed with CH. The incidence of CH increased with lower GA, moving from 4.8% [CI, 3.4-6.1%] at GA 31 w to 16.9% [CI, 8.3-25.4%] at GA <26 w. Among the CH subjects, 57.7% [CI, 53.1-62.2%] were identified after the first screening and classified as delayed thyrotropin elevation (dTSH). With the decrease of GA, the proportion of dTSH also increased, moving from 38.1% [CI, 27.5-48.7%] at GA 31 w to 82.6% [CI, 65.8-99.4%] at GA <26 w. Through conducting weekly screening of thyroid function, it was remarkable that only 42.3% [CI, 37.8-46.9%] of CH subjects were diagnosed during the first screening. The cumulative rate of CH identified by rescreening performed at the second, third, and fourth week was 76.1% [CI, 72.2-80.0%], 90.6% [CI, 87.9-93.3%], and 98.9% [CI, 97.9-99.9%], respectively. Conclusion: The incidence of CH and dTSH both increase with lower GA in VPIs. Dynamic screening of thyroid function by weeks within the first month of life is crucial for the timely diagnosis and treatment of CH in VPIs, and it might effectively reduce the implications of missed diagnosis and delayed treatment. Clinical Trials Registration: ChiCTR1900025234 and ChiCTR2000037918 (Registration number).

Combined genetic screening and traditional newborn screening to improve the screening efficiency of congenital hypothyroidism

Background

Congenital hypothyroidism (CH) is an neonatal endocrine disorder. Traditional newborn screening is the mainstream method of CH screening, so as to ensure the early detection and treatment of CH. This method is limited as it has high rates of false positives and negatives. Genetic screening can be used to address the shortcomings of traditional newborn Screening (NBS); however, the comprehensive clinical value of genetic screening is yet to be systematically studied.

Methods

A total of 3,158 newborns who accepted the newborn screening and genetic screening were recruited for this study. Biochemical screening and genetic screening were performed at the same time. The level of TSH with the DBS was detected by time-resolved immunofluorescence assay. High-throughput sequencing technology based on targeted gene capture was used for genetic screening. The suspected neonatal was recalled and tested serum TSH, and FT4. Finally, the effectiveness of traditional NBS and combined screening was compared.

Results

In this study, 16 cases were diagnosed by traditional NBS. 10 cases of DUOX2 mutation were found in newborn CH-related genetic screening, including 5 homozygous and 5 compound heterozygous variations. We found that the c.1588A > T mutations in DUOX2 constituting the predominant site in the present cohort.Compared with NBS and genetic screening, the sensitivity of combined screening increased by 11.1% and 55.6%, respectively. Compared with NBS and genetic screening, the negative predictive value of combined screening increased by 0.1% and 0.4%, respectively.

Conclusions

Combined traditional NBS and genetic screening reduces the false negative rate of CH screening and improves the early and accurate identification of neonates with CH. Our research explains the mutation spectrum of CH in this region, and provisionally demonstrates the necessity, feasibility and significance of genetic screening in newborns and provides a solid basis for future clinical developments.

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.

Thyroid Function in 509 Premature Newborns Below 31 Weeks of Gestational Age: Evaluation and Follow-up

OBJECTIVE

Preterm and low birth weight (LBW) neonates may present with thyroid dysfunction during a critical period for neurodevelopment. These alterations can be missed on routine congenital hypothyroidism (CH) screening which only measures thyroid stimulating hormone (TSH). The objective of this study was to evaluate a protocol for thyroid function screening (TFS) six years after national implementation.

METHODS

Serum TSH and free thyroxine (fT4) were measured during the second week of life in neonates below 31 weeks. Patients with abnormal TFS (fT4 <0.8 ng/dL and/or TSH >5 mU/L) were followed up with repeated tests until normal levels were reported. Patients who were still on levothyroxine (LT4) at three years of age were re-evaluated.

RESULTS

Five-hundred and nine neonates were included. Thyroid dysfunction was detected in 170 neonates (33%); CH n=20 (3.9%) including typical CH n=1; delayed TSH elevation CH n=19; hypothyroxinemia of prematurity (HOP) n=15 (2.9%); and transient hyperthyrotropinemia n=135 (26.5%). Twenty-one neonates (4.1%) were treated (20 for CH and 1 for HOP). At 3-year follow-up only three patients were diagnosed with permanent CH and still need treatment. LBW infants tended to have TSH levels higher than those with adequate weight.

CONCLUSION

This protocol was able to detect thyroid dysfunction in preterm neonates who were not identified by the current program based on TSH determination in whole-blood. This thyroid dysfunction seems to resolve spontaneously in a few months in the great majority of neonates, but in some cases LT4 could be needed. There is a critical need for specific guidelines regarding the follow-up and re-evaluation of transient CH in preterm neonates.

Hypothyroxinemia in sick term neonates and its risk factors in an extramural neonatal intensive care unit: a prospective cohort study

Objective

Thyroid functions in the sick newborns may be altered in the first week of life. Transient hypothyroxinemia has been reported in these babies, which could be due to the immaturity of the hypothalamic-pituitary-thyroid axis or to acute illness. We conducted this study to estimate the incidence of hypothyroxinemia and determine its risk factors in sick term newborns.

Materials and methods

We analyzed free T4 (FT4) and thyroid-stimulating hormone (TSH) levels in sick term neonates (≤7 days of life) admitted to the neonatal intensive care unit. FT4 and TSH levels were estimated in the first week of life in all the enrolled neonates (N = 98) and then repeated at 14-21 days of life in 46 babies. Risk analysis was conducted using univariate and multivariate logistic regression, and numerical data was compared using the Mann-Whitney U test and t-test.

Results

Hypothyroxinemia was seen in 10 (10.2%) of the admitted term babies. Male gender, vaginal delivery, presence of hypoxic ischemic encephalopathy, and need for mechanical ventilation (>24 hours) were identified as risk factors. There was a significant negative linear correlation between FT4 level in the first week of life and duration of hospital stay.

Conclusion

Hypothyroxinemia is common in sick term neonates.

Utility of Repeat Testing for Congenital Hypothyroidism in Infants with Very Low Birth Weight

OBJECTIVE

To assess for possible missed hypothyroidism in infants of very low birth weight (VLBW) whose initial newborn screening (NBS) was within normal reference range.

STUDY DESIGN

We analyzed serum thyroid-stimulating hormone (TSH) obtained at 36 weeks of corrected gestational age or at hospital discharge if earlier (retest TSH) in infants with VLBW in the neonatal intensive care unit to determine the prevalence and factors associated with retest TSH ≥5 mU/L, a concentration requiring close follow-up for hypothyroidism. Utility of alternative cut-offs for NBS TSH also was assessed.

RESULTS

A total of 398 infants, median gestational age 29 (range 22-36) weeks, birth weight 1138 (470-1498) g, were included in this study. Retest TSH was obtained at 49.5 (12-137) days after birth. Median retest TSH was 3.1 (0.5-27.9) mU/L. Seventy-three (18.3%) of the cohort had retest TSH ≥5 mU/L. Adjusting NBS cut-off to ≥15 or ≥10 mU/L identified <50% of infants with TSH ≥5 mU/L, resulting in 6% false positives and >70% false negatives. Multiple regression modeling indicated that 35% of variance in retest TSH value was explained by NBS TSH concentration, birth weight, and gestational age, all P < .01.

CONCLUSIONS

Retesting for hypothyroidism at 36 weeks of corrected gestational age in infants with VLBL and normal NBS could identify infants who require ongoing surveillance until thyroid function has been definitively ascertained. Adjusting NBS TSH cutoffs is not a valid option for identifying potential hypothyroidism in infants with VLBW because of lack of sensitivity and unacceptable false-positive and false-negative rates.

The prevalence of hypothyroxinemia in premature newborns

Congenital hypothyroidism diagnosed by TSH assessment in bloodspot screening may be overlooked in preterm newborns due to immaturity of the hypothalamus-pituitary-thyroid axis in them. The purpose of the study was to determine the prevalence and causes of hypothyroxinemia in preterm newborns, determined by TSH and FT4 serum concentration measurement, performed on the 3-5^th day of life. We assessed TSH, FT4 and FT3 serum concentration on the 3-5^th day of life in preterm children born at our centre within three consecutive years. We assessed the incidence of hypothyroxinemia, and its cause: primary hypothyroidism, secondary hypothyroidism or low FT4 syndrome - with normal TSH concentration, its dependence - among others - on gestational age (GA), birth body weight (BBW) and being SGA. A total of 525 preterm children were examined. FT4 concentration was decreased in 14.9% of preterm newborns. The most frequent cause of hypothyroxinemia was low FT4 syndrome (79.5%). More than 92% cases of hypothyroxinemia occurred in children born before the 32^nd week and/or with BBW below 1500 g. Thus, every fourth child in these groups had a reduced FT4 concentration. Neonates with hypothyroxinemia were significantly lighter than those with normal FT4. In older and heavier neonates with hypothyroxinemia, serious congenital defects were observed. Neither IVH nor SGA nor twin pregnancies predispose children to hypothyroxinemia. Among newborns with untreated hypothyroxinemia in whom TSH and FT4 assessment was repeated within 2-5 weeks, a decreased FT4 concentration was confirmed in 56.1% of cases. As hypothyroxinemia affects 25% of newborns born before the 32^nd week of gestation and those in whom BBW is less than 1500g, it seems that in this group of children the newborn screening should be extended to measure serum TSH and FT4 concentration between the 3-5^th day of life. In older and heavier neonates, additional serum TSH and FT4 assessment should be limited to children with severe congenital abnormalities but not to all SGA or twins. Despite the fact that the most common form of preterm hypothyroxinemia is low FT4 syndrome, it should be emphasized that FT4 remains lowered on subsequent testing in more them 50% of cases.

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.

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.

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.

Congenital Hypothyroidism: A 2020-2021 Consensus Guidelines Update-An ENDO-European Reference Network Initiative Endorsed by the European Society for Pediatric Endocrinology and the European Society for Endocrinology

Background: An ENDO-European Reference Network (ERN) initiative was launched that was endorsed by the European Society for Pediatric Endocrinology and the European Society for Endocrinology with 22 participants from the ENDO-ERN and the two societies. The aim was to update the practice guidelines for the diagnosis and management of congenital hypothyroidism (CH). A systematic literature search was conducted to identify key articles on neonatal screening, diagnosis, and management of primary and central CH. The evidence-based guidelines were graded with the Grading of Recommendations, Assessment, Development and Evaluation system, describing both the strength of recommendations and the quality of evidence. In the absence of sufficient evidence, conclusions were based on expert opinion. Summary: The recommendations include the various neonatal screening approaches for CH as well as the etiology (also genetics), diagnostics, treatment, and prognosis of both primary and central CH. When CH is diagnosed, the expert panel recommends the immediate start of correctly dosed levothyroxine treatment and frequent follow-up including laboratory testing to keep thyroid hormone levels in their target ranges, timely assessment of the need to continue treatment, attention for neurodevelopment and neurosensory functions, and, if necessary, consulting other health professionals, and education of the child and family about CH. Harmonization of diagnostics, treatment, and follow-up will optimize patient outcomes. Lastly, all individuals with CH are entitled to a well-planned transition of care from pediatrics to adult medicine. Conclusions: This consensus guidelines update should be used to further optimize detection, diagnosis, treatment, and follow-up of children with all forms of CH in the light of the most recent evidence. It should be helpful in convincing health authorities of the benefits of neonatal screening for CH. Further epidemiological and experimental studies are needed to understand the increased incidence of this condition.

The Impact of Seasonal Changes on Thyroxine and Thyroid-Stimulating Hormone in Newborns

Newborn screening for congenital hypothyroidism (CH) is performed by measuring the concentration of thyroxine (T4) and/or thyroid-stimulating hormone (TSH) in dried blood spots. Unfortunately, the levels of T4 and TSH vary due to multiple factors, and therefore the false-positive rate for the test is a challenge. We analyzed screening data from 2008 to 2017 to determine the effect of seasonal changes and manufacturer kit lot changes on T4 and TSH values and on numbers of infants referred. Over a 10-year period, we screened 2.4 million infants using commercially available fluoroimmunoassays to measure T4 and TSH concentrations in dried blood spots. During colder months, daily mean T4 and TSH values were higher and referral rates and false-positive rates were higher. However, there was no significant difference between the number of confirmed CH cases. Furthermore, in rare instances, we observed differences in T4 daily mean values during the 10-year period when manufacturer kit lot changes were made. Seasonal temperature variations influence measured T4 and TSH values and consequently lower the positive predictive value for CH testing in colder months. Newborn screening (NBS) programs should be aware that manufacturer kit lot changes may also influence T4 values.

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.

Newborn Screening for Congenital Hypothyroidism: the Benefit of Using Differential TSH Cutoffs in a 2-Screen Program

CONTEXT

Analysis of a 2-screen program for congenital hypothyroidism (CH) was performed using differential dried-blood spot thyrotropin (bTSH) cutoffs of 10 mU/L at first screening (all infants) and 5 mU/L at second screening (selected infants).

OBJECTIVES

This work aimed to characterize CH infants identified by the second screening and compare infants with bTSH of 5.0 to 9.9 and 10 mU/L or greater on second screening.

DESIGN AND PATIENTS

Maternal and neonatal clinical features were retrospectively analyzed for 119 CH babies detected on the second screen in the Lombardy region of Italy, 2007 to 2014.

RESULTS

Fifty-two (43.7%) of the 119 CH neonates showed bTSH values ranging from 5.0 to 9.9 mU/L at the second screening (low bTSH group) and 67 (56.3%) bTSH of 10.0 mU/L or greater (high bTSH group). The frequency of thyroid dysgenesis and eutopic gland was similar in both groups, as was the frequency of permanent and transient CH. Moreover, a high frequency of extrathyroidal malformations was found in both groups. The percentage of preterm infants (57.7% vs 23.9%, P < .001) and infants admitted to the neonatal intensive care unit (50.0% vs 17.9%, P < .001) was significantly higher in the low vs the high bTSH group. In addition, maternal treatment with glucocorticoids in pregnancy was significantly more frequent in the low bTSH group than in the high bTSH group (11.5% vs 1.5%, P = .042), as well as maternal hypothyroidism and/or goiter (26.9% vs 10.4%, P = .036).

CONCLUSIONS

This study has demonstrated that a lower TSH cutoff at the second screening can detect additional cases of CH and that a second bTSH cutoff of 5.0 mU/L is appropriate for identifying preterm newborns and babies with associated risk factors.

[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.

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

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

Reference Percentiles and Changes over Time for Total Thyroxine in Preterm Infants: A Retrospective Cohort Study

Hypothyroxinemia of prematurity increases the rate of false-positive results in total thyroxine (tT4)-based screening programs for congenital hypothyroidism. The use of specific cutoff values for preterm infants has been proposed, but data on tT4 reference ranges in this population are limited. The primary aim was to establish reference percentiles for tT4 in dried blood spots among Mexican preterm infants. Secondary aims included a comparison of the change of tT4 concentrations over time according to gestational age and to discuss its impact on tT4-based screening programs. This was a retrospective cohort study; 1561 preterm infants were included. Percentile 10th for tT4 concentration at 24-27, 28-30, 31-34, and 35-36 weeks of gestational age, measured in the first week of life was: 47.6, 56.6, 82.3, and 117.1 nmol/L, respectively. tT4 concentrations were compared in three different time points: first week of life, 2-3 weeks of life, and term-corrected gestational age (38 weeks of gestation), progressively increased in infants below 30 weeks, remained stable in infants from 31 to 34 weeks, and decreased in late preterm newborns (35-36 weeks). This study suggests that preterm infants may require the use of lower tT4 cutoff values in newborn screening.

Congenital Hypothyroidism: 8-Year Experience Using 2 Newborn Screens in Alabama

BACKGROUND/AIMS

Newborn screening protocols for congenital hypothyroidism (CH) vary as to whether a TSH or T4 algorithm or some combination is performed. We aimed to determine the 3-year clinical outcome of infants diagnosed with CH and screen-positive for CH using a 2-screen protocol that measures both T4 and TSH on all specimens.

METHODS

Retrospective analysis of patients with CH who were detected by first (NBS1) or second (NBS2) newborn screen in Alabama (2009-2016) and followed at our university-based practice. Clinical follow-up established the final diagnoses in 146 patients, including a subset of 72 patients with eutopic glands.

RESULTS

168 patients were studied: 139 (83%) were detected by NBS1 and 29 (17%) by NBS2. Screening T4 concentrations were 45% reduced in NBS2 compared to NBS1 (p= 0.0002). Thyroid dysgenesis was present in 55% of NBS1 patients while all in NBS2 were eutopic. Follow-up of 146 patients confirmed permanent CH in 92 patients in NBS1 (75%) and 5 in NBS2 (20%). Hispanic infants were only detected by NBS1, and 93% had permanent CH. Transient CH was associated with congenital heart disease. In patients with eutopic, permanent CH, dyshormonogenesis was confirmed in 23% of NBS1 patients and 40% of NBS2. One case of central CH was detected by each screen.

CONCLUSIONS

This 8-year, retrospective study buttresses the importance of a 2-screen approach for CH by identifying 5 infants with clinically significant permanent thyroid dysfunction including dyshormonogenesis and central hypothyroidism. It is the first 2-screen study to incorporate thyroid ultrasound. Disconcertingly, 4 of 5 second-screen infants with permanent CH had no risk factors for CH, and these infants would otherwise not have been detected.

Neonatal Screening for Congenital Hypothyroidism: What Can We Learn From Discordant Twins?

CONTEXT

Newborn screening program for congenital hypothyroidism (CH) adopting rescreening in at-risk neonates.

OBJECTIVES

To estimate the concordance rate for CH in twin pairs discordant at the first screening; to verify whether long-term follow-up of healthy cotwins belonging to CH discordant pairs may be useful to diagnose thyroid hypofunction during development; to evaluate the importance of genetic and environmental influences on liability to permanent and transient CH.

DESIGN AND PATIENTS

Forty-seven screening discordant twin pairs were investigated. Proband was defined as the twin in the pair with a positive test at the first screening and a confirmed diagnosis of CH.

RESULTS

Seven screening discordant twin pairs became concordant for CH within the first month of life (pairwise concordance of 14.9%) because seven screening negative cotwins showed high TSH values when retested. During long-term follow-up (range, 3 to 21 years), hypothyroidism was diagnosed in two monozygotic screening negative cotwins at the age of 9 months and 12 years, respectively. Furthermore, the twin analysis showed that 95% of liability to transient CH was explained by genetic factors and 5% by environmental (unshared) factors, whereas 64% of phenotypic variance of permanent CH was explained by common environmental factors (shared during the fetal life) and 36% by unshared environmental factors.

CONCLUSIONS

This study showed that the introduction of rescreening permits the diagnosis of CH in a greater number of twins. It also showed the importance of long-term follow-up in both twins in the pair, and the role of nongenetic factors in the etiology of permanent CH.

Congenital hypothyroidism in preterm infants: a 3- to 8-year longitudinal study in southern Thailand

Background Preterm infants are at high risk of developing congenital hypothyroidism (CH) due to the immaturity of the hypothalamic-pituitary-thyroid (HPT) axis, loss of iodine supply from the mother and preterm health problems. Objectives To study the incidence and etiologies of CH in preterm infants who were born or admitted in our institute during 2010-2015. Methods The medical records of preterm infants diagnosed with CH as defined by the thyroid-stimulating hormone (TSH) level at the time of the first or second screening >10 mU/L and/or free T4 < 1.00 ng/dL were reviewed. Results Of 2777 preterm infants, 73 cases (2.6%) were diagnosed as CH. The average TSH levels at the first and second screenings were 20.85 and 15.42 mU/L, respectively. The patients were treated with thyroxine at an average initial dosage of 15 μg/kg/day. At 2-3 years of age, after thyroxine discontinuation for 6-10 weeks and regular thyroid function tests for 2 years, 58 patients (79.5%) were diagnosed as having transient CH and 15 patients (20.5%) were diagnosed as having permanent CH. We found no clinical or laboratory parameters in the neonatal period that could differentiate permanent from transient CH. Thyroid scintigraphy (99 m pertechnetate) revealed two patients (13.3%) with ectopic thyroid, one with thyroid hypoplasia (6.7%), eight with normal thyroid (53.3%) and four with enlarged thyroid (26.7%). Conclusions CH was common in preterm infants with an estimated incidence of 2.6%. Thyroxine should be given to preterm infants with higher initial values of TSH >10 mU/L in order to prevent delayed treatment of permanent CH that could be confirmed later.

Screening and management of thyroid dysfunction in preterm infants

Preterm infants can suffer various thyroid dysfunctions associated with developmental immaturity of the hypothalamic-pituitary-thyroid axis, postnatal illness, medications, or iodine supply. The incidence of thyroid dysfunction among preterm infants is higher than that among term infants and has been increasing with improvement in the survival of preterm infants. Hypothyroxinemia is frequently observed during the first week of life in extreme preterm neonates, and the incidence of delayed thyrotropin elevation is high at the age of 2-6 weeks. Although the necessity of routine rescreening remains controversial, recent guidelines on screening for congenital hypothyroidism have recommended rescreening of all preterm neonates. Thyroid hormone replacement is recommended for persistent thyrotropin elevation with or without hypothyroxinemia. Hypothyroxinemia without thyrotropin elevation does not require treatment, and some potential risks of levothyroxine supplementation have been reported. Although most thyroid dysfunctions are transient, careful follow-up after discontinuation of levothyroxine is considered so as to avoid missing persistent hypothyroidism.

Neonatal screening in the Czech Republic: increased prevalence of selected diseases in low birthweight neonates

Neonates with low birthweight (LBW) represent a vulnerable population. This retrospective study analyzed the birth frequency of diseases detected by neonatal screening (NBS) in normal and LBW neonates in the Czech Republic. Between years 2002 and 2016, the number of screened disorders in the Czech Republic gradually increased from two to 13. Prevalence of screened diseases was calculated for cohorts ranging from 777,100 to 1,277,283 neonates stratified by birthweight. Odds ratio of the association of LBW with each disease was calculated and statistical significance was evaluated using the chi-square test or Fisher's exact test, as appropriate. Three diseases were associated with higher risk of prevalence in LBW neonates, namely congenital hypothyroidism (OR 2.50, CI 1.92; 3.25), cystic fibrosis (OR 2.44, CI 1.51; 3.94), and long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) (OR 7.74, CI 2.18; 27.42).Conclusion: Although the underlying mechanisms are not well understood, results can be hypothesized that LBW (respectively prematurity) may lead to the secondary and often transitory hypothyroidism while cystic fibrosis and LCHADD may manifest already prenatally and result into preterm birth and LBW. What is Known: • The percentage of low birthweight (LBW) neonates in the Czech Republic has been increasing. • Previously published studies reported positive association between LBW and congenital hypothyroidism and cystic fibrosis. What is New: • The association between LCHADD and LBW has not yet been described. • LBW can be the first manifestation of cystic fibrosis and LCHADD.

Small for gestational age is a risk factor for the development of delayed thyrotropin elevation in infants weighing less than 2000 g

OBJECTIVE

Delayed thyrotropin (TSH) elevation (dTSHe) is common in low birthweight infants. We aimed to clarify the risk factors for the development of dTSHe in infants weighing <2000 g at birth.

PATIENTS AND METHODS

According to Japanese guidelines, infants with birthweight <2000 g underwent second capillary TSH screening within 30 days, either at 1 month of age; or when weight reached 2.5 kg; or at discharge. dTSHe was defined as TSH >20 mIU/L by venous sampling following a normal result (<15 mIU/L) at first screening aged 4-6 days. For each infant who developed dTHSe three babies without dTSHe were selected and matched for gestational age and birth year. Small for gestational age (SGA) was defined as a birthweight <10th percentile for the gestational age and sex. A multivariate analysis was performed to identify risk factors for the development of dTSHe.

RESULTS

Among the 911 study infants, 17 infants (1.9%) had dTSHe. The median (range) birthweight in the dTSHe group (796 [388-1912] g) was significantly smaller than the comparison group (961 [408-1981] g) (P = 0.04). The number (%) of SGA infants was significantly higher in the dTSHe group (12 [71%]) than in the comparison group (13 [25%]) (P = 0.001). The multivariate analysis revealed that SGA was an independent risk factor for the development of dTSHe (adjusted odds ratio, 9.0; 95% confidence interval, 2.5-32.8; P = 0.001).

CONCLUSIONS

Small for gestational age is an independent risk factor for the development of dTSHe in infants with a birthweight <2000 g. The influence of prematurity, a matching criterion for this study, on dTSHe requires additional study.

The complex aetiology of cerebral palsy

Cerebral palsy (CP) is the most prevalent, severe and costly motor disability of childhood. Consequently, CP is a public health priority for prevention, but its aetiology has proved complex. In this Review, we summarize the evidence for a decline in the birth prevalence of CP in some high-income nations, describe the epidemiological evidence for risk factors, such as preterm delivery and fetal growth restriction, genetics, pregnancy infection and other exposures, and discuss the success achieved so far in prevention through the use of magnesium sulfate in preterm labour and therapeutic hypothermia for birth-asphyxiated infants. We also consider the complexities of disentangling prenatal and perinatal influences, and of establishing subtypes of the disorder, with a view to accelerating the translation of evidence into the development of strategies for the prevention of CP.

Gender disparities in screening for congenital hypothyroidism using thyroxine as a primary screen

OBJECTIVE

Newborn screening for congenital hypothyroidism (CH) is based on testing for the markers thyroxine (T4) and/or thyroid-stimulating hormone (TSH). Diagnosis of CH is complicated because many factors affect the levels of these hormones including infant birth weight, prematurity and age at specimen collection. We investigated whether the sex of the newborn affected the levels of T4 and TSH and consequently the outcome of newborn screening.

DESIGN

In New York State, the Newborn Screening program initially tests all infants for T4 and any baby with a result in the lowest 10% is triaged for TSH screening. We analyzed data from 2008 to 2016 to determine mean and median T4 and TSH values and how these results correlate with the sex of infants who are reported as borderline, referred and confirmed with CH.

METHODS

T4 and TSH concentrations in dried blood spots were measured using commercially available fluoroimmunoassays.

RESULTS

From 2008 to 2016, of the 2.4 million specimens tested for thyroxine, 51.5% were from male and 48.5% were from female infants. Male infants constituted 60% of specimens triaged for TSH testing, 64.9% of repeat requests and 59.6% of referrals, but only 49% of confirmed CH cases. The mean and median T4 values were lower (a difference of approximately 0.8-1.1 μg/dL each year) and the median TSH values were higher in male compared to female infants.

CONCLUSIONS

Natural differences in thyroid hormone levels in male and female infants leads to male infants being disproportionately represented in the false-positive category.

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 healthy and unhealthy preterm newborns

BACKGROUND

The thyroid gland and hormonal regulation are among the most important systems to be investigated in pre-term infants. This study sought to investigate thyroid hormone levels of healthy and unhealthy pre-term infants.

METHODS

The prospective study included 53 consecutive premature infants admitted to the neonatal intensive care unit within a duration of one year. Of these preterm babies, 20 were healthy, while 33 had problems such as asphyxia or RDS. Venous blood samples were collected at baseline 0-24 hours, 7 and 14 days and FT3, FT4, and TSH levels were determined. Other data recorded included demographic characteristics of the patients and clinical variables.

RESULTS

The most frequent health problems were RDS (87.9%), sepsis (30.3%), and retinopathy of prematurity (24.2%). The mean TSH levels showed a consistent decline at three consequent measurements in both groups, which were always significantly lower in unhealthy pre-terms. In both groups, TSH levels showed significant decreases on Day 7 and Day 14 compared to the baseline levels (p<005). The levels of FT3 and FT4 consistently showed significant correlations with gestational week and birth weight at each of the three measurements.

CONCLUSION

Pre-term infants, especially those having problems, have significant hypothyroxinemia that may require thyroid hormone replacement therapy.