Evolution of thyroid function in preterm infants detected by screening for congenital hypothyroidism

Paediatric thyroid disease

The spectrum of thyroid disorders presenting to paediatricians is different to that seen by adult physicians. Referrals reflect cases detected by the neonatal screening programme for congenital hypothyroidism and many of the inherited defects of thyroid hormone generation or action will be manifest in early life. Autoimmune thyroid disease can be particularly challenging to manage in the young and the potential impact of thyroid status on neurodevelopment and schooling are key considerations throughout childhood and adolescence.

Hypothyroidism in Patients with Down Syndrome: Prevalence and Association with Congenital Heart Defects

This population-based study aimed to assess the prevalence of congenital hypothyroidism (CH) and overt hypothyroidism (OH) and their association with congenital heart defects (CHDs) in patients with Down syndrome (DS). The population included all live births residing in Tuscany (Italy) diagnosed with DS recorded in the Registry of Congenital Defects and in the Registry of Rare Diseases of Tuscany in the years 2003-2017. The prevalence of CH and OH in DS patients was calculated by sex and by period. The association of CH and OH with CHDs in DS patients was assessed using multivariate logistic regression. The cohort included 228 subjects. The prevalence of CH and OH was 11.4% (95%CI: 7.4-16.7%) and 12.7% (95%CI: 8.5-12.3%), respectively, with no significant difference by sex. A significant increase in the prevalence of CH (p < 0.0001) was found in the years 2010-2017 compared to the previous period, and among preterm infants (p = 0.009). The presence of CH was associated with a higher prevalence of CHDs (adjusted OR = 2.24, p = 0.082). A significant association between ventricular septal defects (VSDs) and the occurrence of OH (adjusted OR = 3.07, p = 0.025) was also observed. This study confirmed the higher prevalence of both CH and OH in DS compared to the general population. Furthermore, the risk of association between DS and CHDs was higher in the presence of CH, while VSDs are associated with OH, providing relevant insights into the epidemiology of hypothyroidism in DS and associated anomalies.

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).

Neonatal Screening for Congenital Hypothyroidism in Preterm Infants: Is a Targeted Strategy Required?

Background: Premature infants are at higher risk of developing congenital hypothyroidism (CH) but the neonatal screening strategy for this population is still debatable. The purpose of this retrospective study is to describe the results of a screening program for CH in a preterm infant cohort. Materials and Methods: All preterm newborns who underwent neonatal screening in the Italian region of Piedmont in the period January 2019-December 2021, were included in this retrospective cohort study. The first thyrotropin (TSH) measurement was performed at 72 hours, whereas the second at 15 days of life. Infants with TSH >20 mUI/L at first detection and >6 mUI/L at second were recalled for a full evaluation of thyroid function. Results: During the study period, 5930 preterm newborns were screened. Based on birthweight (BW), the mean TSH was 2.08 ± 0.15 for BW <1000 g, 2.01 ± 0.02 for BW 1001-1500 g, 2.28 ± 0.03 for BW 1501-2499 g, and 2.41 ± 0.03 mUI/L in normal-weight newborns (p < 0.005) at the first detection, with a significant difference observed at the second measurement (p < 0.005). Based on gestational age, the mean TSH at first detection was 1.71 ± 0.09 mUI/L for extremely preterm babies and 1.87 ± 0.06, 1.94 ± 0.05, and 2.42 ± 0.02 mUI/L for very preterm, moderately, and late preterm infants (p < 0.005), respectively. Significant between-group differences of TSH measurements were also at the second and third detections (p < 0.005 and p = 0.01). The 99% reference range in this cohort overlapped with the recommended TSH cutoffs for screening recall (8 mUI/L for first detection and 6 mUI/L for second detection). CH incidence was 1:156. Of the 38 patients diagnosed with CH, a eutopic gland was present in 30 (87.9%), with CH transient in 29 (76.8%). Conclusions: We observed no significant difference in the recall rate between preterm and at term infants screened in this study. Our current screening strategy therefore appears effective in avoiding misdiagnosis. CH screening approaches vary among countries. Development and testing of a uniform multinational screening strategy is needed.

Evolution of Subclinical Hypothyroidism Diagnosed in the First 3 Months of Life in Newborns Living in North Italy: A Retrospective Cohort Study

BACKGROUND

Subclinical hypothyroidism (SH) management in neonatal age opens important questions. We aimed to describe the evolution over time of subclinical hypothyroidism diagnosed in the first three months of life in a population of full-term neonates.

METHODS

A single-center longitudinal retrospective cohort study in a tertiary care center was conducted. We recruited 32 subjects with SH diagnosed within the first three months of life. We collected clinical, biochemical, and ultrasound data for every subject at the first examination and every six months until four years of age.

RESULTS

A total of 43.8% of subjects showed stimulating thyroid hormone (TSH) levels over the limit of 10 mUI/L and underwent treatment (Group 1). Eleven subjects started therapy at the first visit, while three subjects started it after a period of observation; 15.6% (Group 2A) showed a trend of TSH decrease and were finally discharged from the follow-up, while 40.6% (Group 2B) showed a TSH level slightly increased, changeless over time.

CONCLUSIONS

We demonstrated that more than half of newborns with hyperthyrotropinemia did not require substitutive therapy showing a positive trend toward normalization or a remaining slight increase compared to normal levels. Moreover, our study suggests the need for a follow-up over time to check the TSH levels course.

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.

Congenital hypothyroidism after newborn screening program reorganization in the Apulia region

Background

Congenital hypothyroidism (CH) is the most frequent congenital endocrine disorder. The purpose of the present study was to evaluate the incidence and etiological classification of CH in Apulia in a three-year period according to the reorganization of the regional screening program in a single central laboratory, as well as to analyze the growth characteristics and the associated risk factors of the CH newborns diagnosed during the study period.

Methods

Data derived from the reorganization of the newborn screening program for CH in a single central laboratory that collects dried blood spot (DBS) from 27 Maternity Hospitals are analyzed over a three-year period. Birth weight and length, daily dose of L-T4 at specific key points (3, 6, 12 and 18 months, 2, 2.5 and 3 years) were also obtained from medical records of the CH newborns during the study period and calculated as standard deviation score (SDS).

Results

The screening program diagnosed 90 newborns with confirmed CH (incidence 1:990; recall rate: 3.6%). In detail, 75.6% newborns had an eutopic thyroid, and 24.4% had thyroid dysgenesis; 33 out of the 90 newborns (36.6%) had one or more risk factors. Among these, the multiple pregnancies are the most important because they tripled the risk of CH. At diagnosis, TSH levels were different between patients with dysgenesis and those with an eutopic thyroid (p = 0.005). Treatment was started at a mean of 18.5 ± 12.8 days of life. The mean starting dose of levothyroxine (L-T4) was 11.38 ± 2.46 μg/kg/day.

Conclusions

The results of these study show an increase of CH cases in newborns with an eutopic thyroid compared to the traditional classification. The centralization of the screening program allows a closer cooperation between laboratory and clinical centers and facilitates the implementation of appropriate diagnostic evaluations and timely initiation of treatment, with positive effects on the management of the condition.

Treatment of hypothyroidism in infants, children and adolescents

In 2014, treatment guidelines from the American Thyroid Association reflected the general consensus that levothyroxine (LT4), adjusted to maintain a normal thyrotropin (TSH) level, is the preferred method for treatment of hypothyroidism. Although this is generally applicable to children, there are subsets of children for whom the diagnosis and treatment of hypothyroidism are problematic. These include children with congenital hypothyroidism (CH), low birth weight (LBW) and very low birth weight (VLBW), Down syndrome (DS), subclinical hypothyroidism, and obesity. In this Review, we focus on the progress and remaining pitfalls in diagnosis and treatment of hypothyroidism in these and other groups.

MECHANISMS IN ENDOCRINOLOGY: The pathophysiology of transient congenital hypothyroidism

Transient congenital hypothyroidism (TCH) refers to congenital hypothyroidism which spontaneously resolves in the first few months or years of life. Currently, there is a paucity of reliable markers predicting TCH at diagnosis, and the diagnosis is established following the withdrawal of levothyroxine therapy around 3 years of age. The incidence of TCH is increasing, and it is a major contributor to the overall increase in the incidence of CH in recent studies. Both genetic factors, in particular mutations affecting DUOX2 and DUOXA2, and environmental factors, for example, iodine deficiency and excess, anti- TSHR antibodies and exposure to antithyroid or iodine-rich medications, may cause TCH. Resolution of TCH in childhood may reflect both normal thyroid physiology (decreased thyroid hormone biosynthesis requirements after the neonatal period) and clearance or cessation of environmental precipitants. The relative contributions and interactions of genetic and environmental factors to TCH, and the extent to which TCH may be prevented, require evaluation in future population-based studies.

Preterm to term infant postmenstrual age reference intervals for thyroid-stimulating hormone and free thyroxine

BACKGROUND

Infants born preterm are affected by a hypothalamic-pituitary-thyroid axis that is immature and still developing as they progress closer to corrected term gestation. Multiple risk factors place preterm infants at risk for a hypothyroid state. However, there is variability in thyroid-stimulating hormone cutoff values and limited data on free thyroxine reference intervals to guide clinicians.

METHODS

1584 thyroid-stimulating hormone and 1576 free thyroxine laboratory samples that were originally collected to screen hospitalized infants for delayed-onset of hypothyroidism were retrospectively evaluated from a group of 1087 infants who ranged in postmenstrual age from 25 to 43 weeks gestation at the time of laboratory sample collection. Median thyroid hormone values and reference intervals were established using R and the mixtools package.

RESULTS

Thyroid-stimulating hormone reference intervals remained similar across gestational ages from 0.340-9.681 µIU/mL in 25-27 6/7-week infants to 1.090-7.627 µIU/mL in 40-43-weeks infants. For the same age groups, free thyroxine reference intervals increased from 0.42-0.91 ng/dL to 0.87-1.32 ng/dL.

CONCLUSION

The reference intervals identified suggest that infants <31 weeks gestation have a higher thyroid-stimulating hormone and lower free thyroxine level at baseline than previously anticipated.

IMPACT

The increasing free thyroxine values in preterm to term infants indicate a maturing hypothalamic-pituitary-thyroid axis. Clinicians need thyroid hormone reference intervals that also vary by postmenstrual age to aid the evaluation of sick preterm infants who are at risk of a delayed hypothyroidism diagnosis that can be missed on the initial newborn screen. This study provides one of the largest samples of thyroid-stimulating hormone and free thyroxine data to establish reference intervals in preterm infants. Clinicians may utilize the identified postmenstrual age-based reference intervals to inform follow-up thyroid testing in preterm infants at several weeks postnatal age.

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.

Correlation Between Thyroid Hormone Concentrations and Ultrasound Thyroid Volume in Preterm Infants Born Before 33 Weeks of Gestation

OBJECTIVE

Thyroid disorders are commonly concomitant with premature birth; however, indications to start therapy remain unclear due to a lack of gestational age (GA)-specific reference ranges. We aimed to evaluate the age-specific thyroid-stimulating hormone (TSH), free thyroxine (FT4) levels and the correlation between TSH and FT4 serum levels and ultrasound thyroid volume in preterm infants.

MATERIALS AND METHODS

This was an observational, prospective, single-center study of 98 preterm infants born before 33 weeks GA. The infants were divided into the 24-28 weeks and 29-32 weeks GA groups. TSH and FT4 serum levels were measured at two time points: at postnatal age (PNA) 2 weeks and at postmenstrual age (PMA) 32 weeks; the results were compared between groups at two consecutive time points.

RESULTS

There was a statistically significant between-group difference in FT4 concentration. There was a positive correlation between FT4 and GA at both screening times. FT4 in the 24-28 weeks GA group was significantly lower than in the 29-32 weeks GA group. The mean (standard deviation [SD]) FT4 at PNA 2 weeks was 11.72 ± 2.16 pmol/l for the 24-28 weeks GA group vs. 13.33 ± 1.80 pmol/l for the 29-32 weeks GA group (p<0.001). The mean (SD) FT4 at PMA 32 weeks was 11.96 ± 1.98 pmo/l for the 24-28 weeks GA group vs. 13.33 ± 1.80 pmol/l for the 29-32 weeks GA group (p=0.001). Our results reflect a slow and gradual upward trend of FT4 in the 24-28 weeks GA. It is of interest that the correlation between thyroid volume and FT4 was statistically significant (rho=0.25, p=0.019) for all studied preterm infants. The correlation between thyroid volume and weight was statistically significant for the entire study group (rho=0.37, p<0.001). We did not find statistically significant differences in TSH and FT4 values between consecutive time points at 24-28 weeks GA. The thyroid volume was not significantly different between both groups. The total thyroid volume was 0.26 vs. 0.27 ml for the 24-28 and 29-32 weeks GA groups, respectively.

CONCLUSION

The results of this study indicate that preterm infants require lower FT4 values depending on GA. Moreover, ultrasound thyroid imaging may facilitate the evaluation of questionable thyroid disorders.

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.

Prevalence of transient congenital hypothyroidism among neonates

OBJECTIVE

Persistence of low levels of thyroid hormone from the time of birth is one of the significant causes of the mental retardation. The aim of this study was to determine the prevalence of transient congenital hypothyroidism among neonates in (XXX).

METHODS

This cross-sectional study, neonates aged 3-5 days who were referred to our center for checkup were screened for thyroid stimulating hormone. Those with TSH < 5mIU/l were, infants were subjected to retesting after one week for TSH and T4 levels. A questionnaire consisting of test results, demographic characteristics, place of sampling, gender, need for re-sampling after the second week for TSH level, birth weight, type of hypothyroidism and prematurity was filled for all the neonates.

RESULTS

Of 3600 neonates screened, 126 were presented with had TSH above 5 mIU/l, of which 7 had high TSH and low T4 and were diagnosed with transient hypothyroidism (5.3%). The mean weight of the neonates with hypothyroidism of significantly lower, p = 0.001. However, the type of delivery was not associated with the prevalence of hypothyroidism, p = 0.999. The relationship between maternal hypothyroidism, preterm birth and intake of antithyroid drugs and transient hypothyroidism was statistically significant, p < 0.001, respectively.

CONCLUSIONS

The incidence of congenital hypothyroidism was 1 in 514 births and was significantly associated with preterm birth, mean weight, maternal hypothyroidism and intake of antithyroid drugs. Routine screening in high prevalence regions are therefore importance, considering the associated factors.

Utility of the New Indian Society of Paediatric and Adolescent Endocrinology (ISPAE) Guidelines for Congenital Hypothyroidism Screening in a High Risk Unit

OBJECTIVE

To study the new ISPAE guidelines in neonates with congenital hypothyroidism and present authors' experience in managing these neonates.

METHODS

A retrospective review of all babies who were screened for congenital hypothyroidism in the institution over a period of 5 y was conducted. Details pertaining to maternal risk factors, neonatal risk factors, screening TSH, venous TSH and details of etiological evaluation including: ultrasound thyroid, technetium 99m scintigraphy and anti thyroid peroxidase antibody estimation were retrieved. The cases were assessed using the new ISPAE guidelines.

RESULTS

During the study period, 8107 babies were screened for congenital hypothyroidism, 83 cases had confirmed disease and 47 had established etiology. There is a fair correlation between screening TSH and venous TSH (r = 0.7, p < 0.05). The estimated incidence of congenital hypothyroidism in present series is 1 in 97 cases. Out of the 83 cases, 36 (43.3%), 16 (19.2%) and 31 (37.3%) cases had screening TSH >20 μIU/mL, 6-20 μIU/mL and < 6 μIU/mL, respectively. Out of the 47 babies with screening TSH <20 μIU/mL, 23 (48.9%), 25 (53.1%) and 12 (25.5%) cases had prematurity, maternal thyroid disease and illness, respectively, as risk factors (some babies had more than one risk factor). Of the 83 cases, all of them had venous TSH >10 μIU/mL and five cases had low Free T4 (<1.1 ng/dl). Thus, none of the cases with congenital hypothyroidism were missed on the new ISPAE guidelines.

CONCLUSION

The new ISPAE guidelines for neonatal screening for congenital hypothyroidism are very useful and applicable in Indian neonates.

Long-Term Course of Hypothyroidism Detected through Neonatal TSH Screening in a Population-Based Cohort of Very Preterm Infants Born at Less than 32 Weeks of Gestation

After several decades of successful newborn screening (NBS) for congenital hypothyroidism, the optimal hypothyroidism NBS algorithm for very preterm infants is still controversial. Due to concerns about an elevated risk of a false-negative initial thyroid-stimulation hormone (TSH) screening, repeat NBS has been implemented for this group. While transient hypothyroidism is known to be more frequent among very preterm infants, the prevalence of permanent hypothyroidism is generally assumed to be the same as in more mature newborns. This study analyses screening and long-term follow-up data from the population-based cohort of 51 infants born from 1999-2017 at less than 32 weeks of gestation and diagnosed with hypothyroidism after NBS in the German Federal State of Bavaria (total number of infants screened 2,107,864). Severe permanent hypothyroidism was always detected at initial TSH screening unless there was a known confounding factor. Cases detected by repeat screening after a negative initial screen most frequently proved to be transient, less frequently mild permanent, or a definitive diagnosis was not possible because of inadequate re-evaluation of the thyroid axis. The prevalence of both permanent and transient hypothyroidism was elevated compared to a cohort of children from the same region born at a higher gestational age. The results seem to support the need for the repeated NBS of very preterm infants. However, as the recommendation to treat mild hypothyroidism is not based on high quality evidence, important issues for future research include treatment outcome studies or even a general review of whether this diagnosis meets the screening criteria. Meanwhile, involving a paediatric endocrinologist in treatment decisions is crucial for optimising the benefit of hypothyroidism screening for this particularly vulnerable group.

Age- and sex-specific reference intervals for thyroid hormones in a Chinese pediatrics: a prospective observational study of 1,279 healthy children

BACKGROUND

Thyroid hormones are essential for early neurocognitive development and growth and development in childhood and adolescence. However, the reference intervals (RIs) for thyroid hormones in Chinese pediatric individuals remain unclear. This study aimed to establish thyroid hormone RIs for a Chinese pediatric population according to appropriate age- and sex-specific partitioning.

METHODS

In this prospective observational study, a total of 1,279 healthy children (singletons, aged from 1 day to 12 years) were recruited, and serum samples were analyzed on a Mindray automated chemiluminescence immunoassay analyzer CL-6000i for thyroid hormone detection, including thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (T3), and total thyroxine (T4). Age and sex-specific RIs were established, and the corresponding 95% confidence intervals (CIs) were calculated in accordance with the Clinical Laboratory Standards Institute (CLSI) document C28-A3 guidelines.

RESULTS

Quantile testing revealed that the median (P50) and RIs [2.5^th percentile (P2.5)-97.5^th percentile (P97.5)] for TSH, FT3, T3, and T4 of males differed significantly from those of females (P<0.05), except for FT4 (P=0.483). For FT3 and T3, the RIs of males were higher than that of females, and the RI of T4 for males was narrower and higher than that of females [P2.5-P97.5: 72.33-171.60 vs. 72.31-176.27 nmol/L; P50: 116.75 vs. 113.47 nmol/L, P=0.011]. RIs for TSH, FT3, FT4, T3, and T4 showed sex- and age-specific properties and displayed a wide variation during the first month of life but gradually narrowed and concentrated with increasing age. In addition, RIs of TSH, FT3, FT4, and T3 in males differed significantly from females in the first month of life (TSH: 1.46-10.87 vs. 1.08-11.35 mIU/L; FT3: 2.96-7.08 vs. 2.35-7.27 pmol/L, FT4: 13.34-28.65 vs. 13.82-31.83 pmol/L; T3: 0.83-2.33 vs. 0.72-2.46 nmol/L). The RI of T4 also exhibited a difference between males and females in the 9- to 12-year age group (59.31-150.72 vs. 63.29-146.94 pmol/L for males and females, respectively).

CONCLUSIONS

Pediatric RIs of thyroid hormones display age- and sex-specific trends. The RIs established in this study will improve the accuracy of TSH assay result interpretations and clinical decision-making in clinical laboratories that utilize the Mindray analytical platform.

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.

Serial Thyroid Function Test in Very Low Birth Weight Neonates

Thyroid dysfunction is more common in preterm and low birth weight infants, and may be missed if thyroid function test (TFT) is not repeated. Thus, we attempted to study the pattern of thyroid function among very low birth weight (VLBW) infants with birth weight less than 1,500 g by serial TFTs. Serum free thyroxine (FT4) and thyrotropin (thyroid-stimulating hormone [TSH]) levels of VLBW infants were tested on fifth to seventh days of life and repeated after 4 weeks of age. Based on serial FT4 and TSH results, abnormal TFT was classified into four groups—transient hypothyroxinemia of prematurity (THOP), transient hyperthyrotropinemia (THT), delayed TSH rise, and overt congenital hypothyroidism (CH). Stata 15.1 (Stata Corp, Texas, United States) was used for analysis. Ninety-six VLBW infants were enrolled with mean gestational age of 30.5 ± 2.7 weeks and median (interquartile range) birth weight of 1,200 (317) g. Out of 96 cases, 30 (31.2%) infants had abnormal TFT. Ten (10.4%) infants had THOP, 7 (7.3%) infants had THT, 11 (11.5%) infants had delayed TSH rise, and 2 (2.1%) infants had overt CH. There were no significant differences in demographic profile and clinical characteristics between neonates with normal and abnormal TFTs. Five infants required levothyroxine supplementation (two infants with overt CH and three infants with delayed TSH rise). VLBW neonates have higher incidence of CH and delayed rise of TSH in this study. In resource-limited settings, repeating TFTs at least once after 4 weeks of age may be suggested to identify delayed rise of TSH which may need intervention.

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.

Incidence of primary congenital hypothyroidism and relationship between diagnostic categories and associated malformations

PURPOSE

The incidence of primary congenital hypothyroidism (CH) has grown progressively and literature data indicate an association between CH and congenital malformations. The purpose of this study is to establish the current incidence of CH in the Italian Region of Piedmont and verify the relationship between CH diagnostic categories and associated malformations.

METHODS

The biochemical and clinical data of 105 newborns with CH diagnosed in the period January 2014 to December 2019 were analyzed.

RESULTS

The incidence of CH in the Italian Piedmont region in the 2014-2019 period increased to 1:1090. Thyroid dysgenesis was responsible for 47.6% (50/105) of all cases, with agenesis in 14.3% (15/105), while ectopia and hypoplasia in 23.8% (25/105) and 9.5% (10/105) of the cases, respectively; dyshormonogenesis defects were found in 52.4% (55/105) of cases. Congenital extra-thyroid anomalies were identified in 33/105 (31.4%) of newborns with CH and mainly involve the cardiac system (17/85, 16.1%), urogenital tract (7/85, 6.7%), gastrointestinal tract (5/105, 4.8%), and the musculoskeletal system (5/105, 4.8%). The highest rate of malformations was observed in patients with thyroid agenesis and dyshormonogenesis, respectively, in 53.5% and 36.4% of cases, while in the presence of thyroid ectopia and hypoplasia, the rate was 12% and 20%, respectively, (p = 0.03).

CONCLUSION

In the Italian region of Piedmont, the incidence of primary CH has been increased over time, with a variation in the percentage of the different forms of CH. Congenital malformations, especially affecting the cardiovascular, urogenital, gastrointestinal, and musculoskeletal systems, seem to be mainly associated with thyroid agenesis or defects in hormonogenesis.

Low free thyroxine and normal thyroid-stimulating hormone in infants and children: possible causes and diagnostic work-up

Screening for hypo- or hyperthyroidism in adults is generally done by measuring the serum thyrotropin (thyroid-stimulating hormone, TSH) concentration. This is an efficient approach in case of suspected acquired thyroid disease. However, in infants and children, congenital hypothalamus-pituitary-thyroid (HPT) axis disorders also need to be considered, including primary and central congenital hypothyroidism, and even rarer thyroid hormone receptor and transporter defects. In primary congenital hypothyroidism, TSH will be elevated, but in the other congenital HPT axis disorders, TSH is usually within the normal range. Free thyroxine (FT4) assessment is essential for the diagnosis in these conditions.Conclusion: Here we discuss a number of rare congenital HPT axis disorders in which TSH is normal, but FT4 is low, and provide a clinical algorithm to distinguish between these disorders. What is Known: • A single thyroid-stimulating hormone (TSH) measurement is an appropriate screening method for primary hypothyroidism. • For central hypothyroidism and rare thyroid hormone receptor and transporter defects a free thyroxine (FT4) measurement is essential for the diagnosis because TSH is usually normal. What is New: • Here we present a new problem-oriented clinical algorithm including a diagnostic flow-chart for low FT4 and normal TSH in infants and children.

[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.

Evolution of congenital hypothyroidism in a cohort of preterm born children

BACKGROUND

Congenital hypothyroidism (CH) is reported to be more common in preterm infants than in term infants, especially in sick preterm infants. Though a frequent possibility of transitory thyroidal alterations in this category of neonates, the evolution of CH to transient or permanent forms is unpredictable.

METHODS

We retrospectively analyzed medical records of 28 preterm infants (<37 weeks gestation) who had exhibited a positive screening for CH at birth during the period 2000-2015 followed in our Center. Children were divided into three groups: permanent CH (PCH) with thyroid dysgenesis, PCH with eutopic normal-sized thyroid gland, and transient CH (TCH) with eutopic normal-sized thyroid gland. In all groups we described clinical and biochemical characteristics. Secondly, we analyzed the differences between patients with thyroid dysgenesis and patients with eutopic normal-sized gland and we compared PCH and TCH groups with normal-sized thyroid gland in order to identify clinical or biochemical data for early detection of transient forms.

RESULTS

Of all patients, 21.4% showed thyroid dysgenesis while 78.6% presented eutopic normal-sized gland. Infants with thyroid dysgenesis had higher median (IQR) baseline s-TSH and levothyroxine (L-T4) dose per weight at 12 months (12 m-dose) than patients with eutopic normal-sized gland. At re-evaluation of the patients with eutopic normal-sized gland, 36% showed PCH and 64% had TCH. The age of the patients at the beginning of L-T4 treatment, gestational age (GA), birth weight, blood thyroid stimulating hormone levels (b-TSH) at first newborn screening (NBS), baseline serum thyroid stimulating hormone (s-TSH), and L-T4 12 m-dose were statistically different between the two groups.

CONCLUSIONS

Our results demonstrate that factors as GA, birth weight, b-TSH levels at first NBS, baseline s-TSH, L-T4 12 m-dose and age at the start of the treatment may be considered useful predictive elements for the evolution of CH.

Response of preterm infants with transient hypothyroxinaemia of prematurity to the thyrotropin-releasing hormone stimulation test is characterized by a delayed decrease in thyroid-stimulating hormone after the peak

OBJECTIVES

We evaluated the response to the thyrotropin-releasing hormone (TRH) stimulation test in very low-birth weight (VLBW) infants to elucidate the aetiology of transient hypothyroxinaemia of prematurity (THOP).

DESIGN AND METHODS

We performed TRH stimulation tests on 43 VLBW infants. Subjects were divided into two groups; a THOP group (N = 11; basal TSH < 15 mU/L and basal FT4 ≤ 0.8 ng/dL) and a non-THOP group (N = 32; basal TSH < 15 mU/L and basal FT4 > 0.8 ng/dL). Basal FT4 and FT3 were measured before, and TSH (0, 30, 60, 90, 120 and 180 minutes) was measured after, the administration of TRH (7 µg/kg). We calculated the ratio of TSH 180 minutes to THS 0 minute as the primary outcome. We also collected data on T3 and rT3 in this study.

RESULTS

In both groups, TSH 30 minutes values were the highest. However, the ratios of TSH 180 minutes to THS 0 minutes in the non-THOP group and the THOP group were (median [IQR]) 1.3 [1.0-1.7] and 3.0 [1.5-5.3] (P < .01). No significant differences were observed in T3 (1.0 [0.8-1.3] and 0.7 [0.4-0.7] ng/mL, P = .06). However, in the THOP group, rT3 was significantly lower than that of the non-THOP group (168.0 [148.1-197.0] and 92.9 [74.7-101.6] pg/mL, P < .01).

CONCLUSIONS

The delayed decrease in the TSH concentration after the peak for the TRH tests and decreased levels of rT3 suggest that the main aetiology for THOP is suppression at the level of the hypothalamus, but not inactivation of peripheral thyroid hormone metabolism.

[A clinical analysis of hypothyroidism in very low birth weight/extremely low birth weight infants]

OBJECTIVE

To study the risk factors and treatment outcome of hypothyroidism in very low birth weight/extremely low birth weight (VLBW/ELBW) infants.

METHODS

The VLBW/ELBW infants who were diagnosed with hypothyroidism from September 2018 to December 2019 were enrolled as the case group (n=29). The children with normal thyroid function, matched at a ratio of 1 : 3, were enrolled as the control group (n=87). Clinical features were compared between the two groups. The correlation of thyroid function with gestational age and birth weight and the risk factors for hypothyroidism were analyzed.

RESULTS

A total of 162 VLBW/ELBW infants who met the inclusion criteria were enrolled, with 29 infants in the case group (an incidence rate of hypothyroidism of 17.9%). The lower the birth weight, the higher the incidence rate of hypothyroidism (P<0.05). Triiodothyronine (T3) and free T3 were positively correlated with gestational age (P<0.05). T3 and free thyroxine were positively correlated with birth weight (P<0.05). Small for gestational age, multiple birth, maternal age ≥ 35 years, and use of dopamine were independent risk factors for hypothyroidism (P<0.05). In the case group, 16 infants were treated with levothyroxine (5-10 μg/kg daily), and the thyroid function returned to normal after 2 weeks of treatment.

CONCLUSIONS

There is a high incidence rate of hypothyroidism in VLBW/ELBW infants. Small for gestational age, multiple birth, advanced maternal age, and use of dopamine are risk factors for hypothyroidism. The infants treated with levothyroxine should be followed up regularly to ensure an appropriate dose.

The natural history of congenital hypothyroidism with delayed TSH elevation in neonatal intensive care newborns

OBJECTIVE

To assess the clinical and neurological outcomes in newborns with primary congenital hypothyroidism presented with delayed TSH elevation (dTSH), and to define parameters that may predict the evolution of transient vs. permanent hypothyroidism in these newborns.

DESIGN AND PATIENTS

An observational study was performed of a cohort of 113 children with a history of dTSH.

MEASUREMENTS

Birth parameters, thyroid screening results, thyroid gland imaging, levothyroxine dose and neurological outcome were compared between newborns with spontaneous recovery and children with a final diagnosis of either transient or permanent hypothyroidism.

RESULTS

Of the children with a history of dTSH, 93% demonstrated recovery, either spontaneously or following levothyroxine treatment (transient hypothyroidism). Newborns with spontaneous recovery demonstrated milder thyroid dysfunction at the newborn screening compared to those who started levothyroxine treatment. Levothyroxine dose was lower in children with transient vs. permanent hypothyroidism only during the first 6 months of life; otherwise, these groups were similar in birth parameters, thyroid screening results and gland images. Seventeen out of 61 children (28%) that underwent neurological assessment demonstrated a developmental delay. Duration of treatment was highly variable in children with transient hypothyroidism.

CONCLUSIONS

Thyroid dysfunction is transient in most cases of dTSH. No reliable parameters can predict a priori transient vs. permanent hypothyroidism.

Hyperthyrotropinemia is common in preterm infants who are born small for gestational age

Background To determine the incidence of congenital hypothyroidism (CH) with a delayed increase in thyroid-stimulating hormone (TSH) levels in preterm infants and to describe the associated factors. Methods A prospective newborn screening (NBS) was conducted in 122 very low birth weight (VLBW) premature neonates born between June 2016 and September 2017. A dried blood spot thyroid stimulating hormone (TSH) level ≥15 mIU/L at 7 and 15 days of life, ≥10 in serum at the second screen or ≥5 at the third screen was defined as positive for CH. A concomitant increase in the TSH level and normal free thyroxine (T4) level was classified as hyperthyrotropinemia (HT). Results Before the first month of life, no cases of CH were identified. However, the second and third NBS identified 10 and six subjects with HT, respectively, but no cases of CH. The overall cumulative incidence of HT was 1:8. Small for gestational age (SGA) was a variable that was significantly associated with HT, even after the exclusion of patients with Down syndrome. Conclusions A high incidence of HT, but not CH, was found after the first month of life in preterm infants. Being SGA was strongly associated with having higher TSH. The need for repeating TSH screening after the first month of life in this population remains to be established.

Follow-up of infants with congenital hypothyroidism and low total thyroxine/thyroid stimulating hormone on newborn screen

PURPOSE

Newborn screening (NBS) methods to detect congenital hypothyroidism (CH) vary regarding whether total thyroxine (T4), thyroid stimulating hormone (TSH), or both are measured. Neonates with low T4 and normal or low TSH (lowT4/TSH) may only be detected by T4-inclusive methods or age-dependent repeat screens. Premature neonates and those with pituitary-hypothalamic disorders frequently manifest lowT4/TSH.

METHODS

This is a retrospective case-study of newborns who were screen-positive for lowT4/TSH in Alabama in 2009-2016 using a combined T4 and TSH method and 2 routine NBS. The clinical, laboratory, and final diagnosis after 3 years were determined.

RESULTS

Over 8 years, 225 infants were referred to our institution for evaluation and treatment of CH. Twelve infants were screen-positive for lowT4/TSH by first or second NBS. Four of the 12 infants had permanent CH (30%): 2 with primary and 2 with central etiologies. One infant with moderately severe central CH was only detected by the routine second NBS. Six of 7 premature infants had elevated TSH on serum confirmation labs consistent with a delay in hypothalamic-pituitary maturation, yet 2 of these patients were later established to have permanent primary CH. While most cases of lowT4/TSH resolved by 3 years of age, several neonates had extended periods of moderate to severe hypothyroxinemia prior to detection and treatment.

CONCLUSION

One third of the infants with lowT4/TSH on NBS in this study had permanent CH. These results emphasize the importance of T4-based assay methods, subsequent (repeat) screens and long-term follow-up in the management of neonates with lowT4/TSH on newborn screen.

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.

Thyroid dysfunction in preterm infants born before 32 gestational weeks

Background

Thyroid hormones are critical for growth and brain development during the newborn period and infancy. Because of delayed maturation of the hypothalamic-pituitary-thyroid axis in preterm infants, thyroid dysfunction is common, and thyroid stimulating hormone (TSH) elevation is often delayed in preterm infants. The objective of this study was to determine the incidence of thyroid dysfunction requiring levothyroxine treatment and to identify its risk factors in preterm infants.

Methods

A retrospective cohort study was performed on preterm infants who were born before 32 gestational weeks and admitted to a single tertiary academic center for more than 8 weeks between January 2008 and December 2014. In these infants, serial thyroid function tests (TFTs) measuring serum TSH and free thyroxine (fT4) were routinely performed at 1, 3, and 6 weeks of postnatal age.

Results

Of the 220 preterm infants enrolled, 180 infants underwent TFTs at 1, 3, and 6 weeks of postnatal age and were included in the study. Of the 180 infants, 35 infants (19.4%) were started on levothyroxine treatment based on the results of serial TFTs. Among the 35 infants who were treated with levothyroxine, 16 infants (45.7%) had normal results on the initial TFT. Three of these 16 infants continued to have normal results on the second TFT. Thyroid dysfunction requiring levothyroxine treatment was significantly associated with maternal pregnancy-induced hypertension (adjusted odds ratio 2.64, 95% confidence interval 1.02–6.81).

Conclusions

Thyroid dysfunction requiring levothyroxine treatment occurred in nearly one-fifth of preterm infants born before 32 gestational weeks. Nearly half of the preterm infants who were treated with levothyroxine had normal TSH and fT4 levels at 1 week of postnatal age. The findings of the present study suggest that serial TFTs is important to find preterm infants who require levothyroxine treatment.

Transient neonatal hypothyroidism secondary to postnatal maternal exposure to contrast medium

We report a preterm breastfed infant who developed a transient hypothyroidism after his lactating mother had a CT scan with iodinated contrast medium, despite the advised 24 hours' pause in breast feeding. The aetiological assessment did not show any other cause for this hypothyroidism. Transient neonatal hypothyroidism after the use of topical iodine is well known, but it has not been described as a complication of intravenous contrast medium administration to a lactating mother. This case highlights the possibility of transient neonatal hypothyroidism secondary to contrast medium exposure to a lactating mother. When imaging is needed in the lactating mother, a longer break in breast feeding might be needed to prevent transient hypothyroidism in the preterm infant.

Initial and delayed thyroid-stimulating hormone elevation in extremely low-birth-weight infants

BACKGROUND

To determine the incidence, etiology, and outcomes of thyroid-stimulating hormone (TSH) elevation in extremely low-birth-weight infants (ELBWIs).

METHODS

Newborn thyroid screening data of 584 ELBWIs (birth weight, < 1000 g; gestational age, ≥ 23 weeks) were retrospectively analyzed to identify initial (≤ 2 postnatal weeks) and delayed (> 2 weeks) TSH elevations. Growth and neurodevelopmental outcomes at 2 years' corrected age (CA) were assessed according to levothyroxine replacement.

RESULTS

Initial and delayed TSH elevations were detected at CAs of 27 and 30 weeks, respectively, with incidence rates of 0.9 and 7.2%, respectively. All infants with initial TSH elevations had perinatal asphyxia, and 95% of those with delayed TSH elevation were exposed to various stressors, including respiratory support, drugs, and surgery within 2 weeks before diagnosis of TSH elevation. Free thyroxine (T4) levels were simultaneously reduced in 80 and 57% of infants with initial and delayed TSH elevations, respectively. Both initial and delayed TSH elevations were transient, regardless of levothyroxine replacement. Infants receiving levothyroxine replacement therapy had significantly higher TSH elevations, significantly lower free T4 levels, and significantly reduced mortality, compared to untreated infants. However, levothyroxine replacement had no significant effect on long-term growth and neurodevelopmental outcomes.

CONCLUSIONS

The timing of insult superimposition on hypothalamic-pituitary-thyroid axis maturation is a major determinant of initial or delayed TSH elevation in ELBWIs. Levothyroxine replacement did not affect growth or neurodevelopmental outcomes in this population.

Thyroid-Stimulating Hormone Reference Ranges for Preterm Infants

BACKGROUND AND OBJECTIVES

Many newborn screening (NBS) programs now perform repeat or serial NBS to detect congenital hypothyroidism. There is wide variation in thyroid-stimulating hormone (TSH) cutoffs used by NBS programs. Data on TSH reference ranges in preterm infants at increasing postnatal age are limited. Our study objective was to determine TSH reference ranges for preterm infants born at <32 weeks' gestation.

METHODS

We analyzed serial TSH levels on NBS performed on infants born between 22 and 31 weeks' gestation from 2012 to 2016 in Wisconsin. The study cohort was divided into 2 groups (22-27 and 28-31 weeks), and TSH percentiles were defined from birth to the term equivalent gestational age.

RESULTS

The study cohort consisted of 1022 and 2115 infants born at 22 to 27 and 28 to 31 weeks' gestation, respectively. The 95th percentile TSH level for the group born at 22 to 27 weeks' gestation gradually decreased and reached a nadir at ∼10 to 11 weeks. In contrast, for the group born at 28 to 31 weeks' gestation, the 95th percentile TSH level reached a nadir at ∼5 to 6 weeks. At 3 to 4 weeks after birth, the 95th percentile TSH level ranged from 11 to 11.8 μIU/mL for the group born at 22 to 27 weeks' gestation and ranged from 8.2 to 9 μIU/mL for the group born at 28 to 31 weeks' gestation.

CONCLUSIONS

Using a statewide cohort of preterm infants, we constructed TSH reference charts from birth to the term equivalent gestation for preterm infants born at <32 weeks' gestation. Use of a single cutoff for all preterm infants might lead to misdiagnosis. The differences in TSH levels according to gestational-age categories might explain the increased frequency in congenital hypothyroidism diagnoses among preterm infants. These data are useful for defining age-adjusted NBS TSH cutoffs for preterm infants.

Increased Congenital Hypothyroidism Detection in Preterm Infants with Serial Newborn Screening

OBJECTIVES

To determine the incidence of congenital hypothyroidism in preterm infants and to identify associated risk factors.

STUDY DESIGN

A population-based cohort study was performed in preterm infants born at <32 weeks of gestational age between 2012 and 2016 in Wisconsin. Newborn screening (NBS) results and demographic data were obtained from the Wisconsin State Laboratory of Hygiene. Congenital hypothyroidism was subdivided to early TSH elevation (eTSH) and delayed TSH elevation (dTSH). Multivariate logistic regression analyses were performed to identify demographic factors associated with dTSH.

RESULTS

A total of 3137 preterm infants born at 22-31 weeks of gestational age were included in the study. Mean gestational age was 28.4 ± 2.4 weeks and mean birth weight was 1191 ± 399 g. Forty-nine infants were diagnosed with congenital hypothyroidism. The overall incidence of congenital hypothyroidism was 1.56%, including a 0.13% incidence of eTSH and a 1.43% incidence of dTSH. Birth weight <1000 g, multiple gestation, and initial TSH level were identified as independent predictors for dTSH.

CONCLUSION

Targeted serial NBS in Wisconsin led to a higher rate of diagnosis of congenital hypothyroidism in preterm infants than has been reported previously. The majority (92%) of congenital hypothyroidism cases were diagnosed with dTSH. Birth weight <1000 g, multiple gestation, and elevated initial TSH level were associated with increased risk for development of dTSH. We recommend obtaining targeted serial NBS in preterm infants (<32 weeks of gestational age) to improve the detection of congenital hypothyroidism.

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.

The effect of thyroid functions on osteopenia of prematurity in preterm infants

Background It is known that thyroid hormones have effects on bone development. In particular, the effect of thyroid hormones on osteopenia of prematurity (OOP) has not been examined in preterm infants. Our study aimed to examine the relationship between OOP and congenital hypothyroidism (CH) in preterm infants. Methods Very low birth weight infants (VLBW, <1500 g) were included in the study. Thyroid-stimulating hormone (TSH) and free thyroxine (fT4) levels were measured on postnatal day 5. Serum calcium, phosphorus and alkaline phosphatase (ALP) levels were studied as standard screening parameters for OOP at postnatal week 4. Patients with serum ALP level >700 IU/L were included in the OOP group. We intended to figure out the relationship between OOP and CH in infants. Results In our study, OOP frequency was 14.9% among 543 VLBW infants. There was no statistically significant difference between groups with and without CH (21.7% and 14.8%, respectively) in terms of OOP (p=0.632). Gestational age (GA) was significantly lower in infants with diagnosed OOP (p<0.001, p<0.001, respectively). In addition, the prevalence rates of mothers with preeclampsia, small for gestational age (SGA), respiratory support requirement, late-onset neonatal sepsis (LOS), bronchopulmonary dysplasia (BPD) and full enteral feeding time were found to be higher in the OOP group (p<0.05). Conclusions We found that thyroid hormones had no effect on OOP in preterm infants. Therefore, future randomized controlled studies as well as long-term outcome studies are warranted on this topic.

Características clínicas de los niños con hipotiroidismo congénito en Santander, Colombia

Introducción. El hipotiroidismo congénito (HC) es la primera causa de retraso mental prevenible. El inicio temprano de su tratamiento con la hormona tiroidea garantiza un desarrollo neurológico normal.Objetivos. Describir la etiología y las manifestaciones clínicas del HC y relacionar la discapacidad cognitiva con el inicio del tratamiento en una serie de casos de niños con esta enfermedad en el departamento de Santander, Colombia.Materiales y métodos. Estudio descriptivo a través de serie de casos. La información se recolectó de historias clínicas de pacientes con HC diagnosticado entre 1999 y 2013 y atendidos por el Servicio de Endocrinología Pediátrica del Hospital Universitario de Santander Empresa Social del Estado. Se analizaron 15 variables en el programa Microsoft Excel 2013.Resultados. Se recolectaron 59 casos, con una relación sexo femenino/masculino de 1.7:1. En el 49.2% de los casos se realizó tamizaje neonatal. Las disgenesias tiroideas fueron la etiología más común; la ictericia neonatal prolongada, la hernia umbilical y la hipotonía fueron las características más frecuentes. El retraso mental se presentó en el 64.4% de los casos.Conclusiones. El tamizaje neonatal es la mejor estrategia para captar la mayoría de los casos e iniciar tratamiento oportuno. En Colombia, la ictericia neonatal prolongada debe alertar un posible caso de HC.

Higher Incidence Rates of Hypothyroidism and Late TSH Rise in Preterm Very-Low-Birth-Weight Infants at a Tertiary Care Center

BACKGROUND/AIMS

Preterm newborns with a very low birth weight (VLBW) of < 1,500 g have an atypical form of hypothyroidism with a delayed rise in TSH, necessitating a second newborn screening specimen collection. The aims of this study were to survey the compliance with second newborn screening to detect delayed TSH rise in VLBW preterm infants at a tertiary care center, and to determine the rate of atypical hypothyroidism.

METHODS

Retrospective review of the records of 104 preterm VLBW infants. Late TSH rise was defined as an increase in TSH concentration after 14 days of age in the presence of a normal initial screen.

RESULTS

The compliance rate was 92% for the second screening. High rates of hypothyroidism (16.3%) and of late TSH rise (4.8%) were detected. Patients with hypothyroidism had a significantly lower birth weight (p = 0.01) and longer hospital stay (p = 0.004). Patients with late versus those with early TSH rise had a significantly lower mean birth weight (851 ± 302 vs. 1,191 ± 121 g, p = 0.004).

CONCLUSION

The rates of early and late TSH rise in this VLBW population were higher than those in the literature and could be due to the use of povidone-iodine disinfectants. The yield of a second TSH screening in this study was high indicating the need for vigilance in screening VLBW preterm infants.

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.

The etiologies and incidences of congenital hypothyroidism before and after neonatal TSH screening program implementation: a study in southern Thailand

BACKGROUND

Congenital hypothyroidism (CH) is one of the common causes of intellectual disability which can be prevented by early detection of an elevated thyroid stimulating hormone (TSH) level in the newborn and by treatment with thyroxine. In Thailand, neonatal TSH screening was implemented nationwide in 2005. The objective of the study was to determine the etiologies and the estimated incidences of CH in southern Thailand before and after the implementation of a neonatal TSH screening program in 2005.

METHODS

The medical records of pediatric patients who were diagnosed with primary CH at Songklanagarind Hospital during 1995-2013 were retrospectively reviewed. The study was divided into two time periods: study period 1 (SP1) (1995-2004) and study period 2 (SP2) (2005-2013), the time before and after TSH program implementation.

RESULTS

The most common form of CH during SP1 was overt permanent CH (66%), mostly caused by athyreosis or ectopic thyroid. In SP2, the most common form of CH was mild permanent CH (39%) (mostly due to dyshormonogenesis), followed by overt CH (32%) and transient CH (29%). The overall annual estimated incidence of CH per 10,000 live births in Songkhla Province was 1.69 (1:5021) in SP1, increasing to 4.77 (1:2238) in SP2; in all 14 provinces in southern Thailand, the estimated incidence was 1.24 (1:8094) in SP1 and 2.33 (1:4274) in SP2.

CONCLUSIONS

Neonatal TSH screening has a significant impact on the increased detection of the mild form of permanent and transient CH cases, which may be important for the prevention of brain damage from less severe CH although this remains to be documented.

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.

Gestational age, not transient hyperthyrotropinemia impacts brain white matter diffusion tensor imaging in premature infants

Transient hypothyroidism is common in premature infants and increases the risk of adverse neurodevelopmental outcomes. Thyroid hormone (TH) is involved in oligodendrocyte development and myelination, however, whether transient hypothyroidism is associated with oligodendrocyte dysplasia and abnormal myelination is unclear. The aim of the present study was to investigate correlations among TH levels, neurodevelopmental outcomes and white matter (WM) microstructure in premature infants. The authors designed a cohort study recruiting 81 premature infants (age, 23-35 weeks). A total of 17 were born with a gestational age (GA) <30 weeks (early preterm group) and 64 of them were born with a GA ≥30 weeks (late preterm group). For outcome measurement, thyroid stimulating hormone (TSH) levels at 0, 18, and 24 h of admission were measured. Neurodevelopmental outcomes were assessed using Bayley III test. Diffusion tensor imaging was used to explore the characterization of WM microstructure. The data demonstrated that GA, however not TSH level was associated with neurodevelopmental outcomes in the following 2 years. Fractional anisotrophy (FA) increased with TSH0 levels over anterior limb of internal capsule, while axial diffusivity decreased with TSH0 levels over splenium of corpus callosum (CC). The late preterm group had more intact WM integrity over the internal and external capsule (EC) in FA compared with the early preterm group. Infants with motor dysfunction had significantly increased mean diffusivity (MD) values at regions of interest in the genu and splenium of CC. The results of the present study demonstrated that GA, however not transient hypothyroidism influenced neurodevelopmental outcomes in the premature infants. FA increased with age in a regionally-specific manner over regions of the internal capsule and EC. MD may act as a potential predictor for motor function in premature babies.

Former Very Preterm Infants Show Alterations in Thyroid Function at a Preschool Age

Preterm birth is frequently associated with altered thyroid hormone levels in the newborn period. Recent data suggest a role of prematurity independent of birth size also in childhood thyroid dysfunction. Whether the high-risk population of former very preterm infants (VPI) is particularly susceptible to thyroid hormone alterations is currently unknown. The aim of the present study was to assess whether former VPI display changes in thyroid hormone status in comparison to term-born controls at a preschool age. Free triiodothyronine (fT3), free thyroxine (fT4), and thyroid stimulating hormone (TSH) concentrations were determined in former VPI and same-aged children born at term at five to seven years of age. 31 former term infants and 82 former VPI were included in the study. In comparison to children born at term, former VPI had lower fT4 (16.1 ± 1.8 versus 17.0 ± 2.1 pmol/l), higher fT3 (6.8 ± 0.7 versus 6.5 pmol/l), and higher TSH levels (3.0 ± 1.4 versus 2.3 ± 1.0 μU/l), independent of major neonatal morbidities. As subclinical changes in thyroid hormone status are potentially associated with adverse health profiles, close follow-up of these children is warranted.