Hypothyroidism In Preterm Infants Research Articles

A novel useful marker in the early discrimination of transient hyperthyrotropinemia/hypothyroxinemia and congenital hypothyroidism in preterm infants: thyroid-stimulating hormone/free thyroxine ratio.

Transient hyperthyrotropinemia/transient hypothyroxinaemia and congenital hypothyroidism (CH) have completely different treatment and clinical outcomes. However, a powerful, highly sensitive and cost-effective marker for the differentiation of these clinical entities in the early postnatal period is not available. Therefore, we aimed to test the potential, early predictive, diagnostic power of the thyroid-stimulating hormone (TSH)/free thyroxine (fT4) ratio for differentiation of the two clinical entities in the early period of life. TSH and fT4 levels were recorded on the postnatal day 7 of premature infants<32weeks of gestational age. TSH/fT4 ratio was calculated. The significance degree of TSH/fT4 ratio was analyzed for the differentiation of transient hyperthyrotropinemia or transient hypothyroxinaemia and CH. The study included 1,204 preterm infants<32weeks of gestational age. Of the 1,204 infants, 978 (81.2 %) had normal thyroid function. Eighty-eight infants (7.3 %) were diagnosed with CH and 138 (11.5 %) with transient hyperthyrotropinemia or transient hypothyroxinemia. Initial TSH/fT4 ratio>4.8 was found to be an early diagnostic warning sign with high power in favor of transient hyperthyrotropinemia or transient hypothyroxinemia (AUC value: 0.947) and TSH/fT4 ratio>12.5 (AUC value: 0.999) was found to be an early diagnostic warning sign with high power in favor of CH (p=0.0001). We found for the first time that the TSH/fT4 ratio can be used for the early differentiation of transient hyperthyrotropinemia/transient hypothyroxinaemia and CH in preterm infants without additional cost and with high power.

Neonatal screening for congenital hypothyroidism (CH) in preterm infants. Is a targeted strategy required?

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. 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 TSH measurement was performed at 72h, while 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. During the study period, 5930 preterm newborns were screened. Based on birth weight (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 cut-offs 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%). 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.

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 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.

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.

Increased Congenital Hypothyroidism Detection in Preterm Infants with Serial Newborn Screening

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

Is It Necessary to Measure T4 In Screening of Congenital Hypothyroidism in Preterm Infants?

Is It Necessary to Measure T4 In Screening of Congenital Hypothyroidism in Preterm Infants?

Optimal Timing of Repeat Newborn Screening for Congenital Hypothyroidism in Preterm Infants to Detect Delayed Thyroid-Stimulating Hormone Elevation

To evaluate the timing of a delayed rise in thyroid-stimulating hormone (TSH) levels in preterm infants with congenital hypothyroidism, and to determine whether cases of congenital hypothyroidism would be missed by using current consensus guidelines of repeat screening at approximately 2 weeks of age or 2 weeks after the first screening. The study was performed over a 13-year period (January 2004-December 2016). Whole-blood TSH samples were collected between 72 and 120 hours after birth. Repeat samples were collected weekly in preterm infants until the infant was term-corrected (37 weeks' gestation). Patients were followed up to determine whether congenital hypothyroidism was permanent or transient. Twenty-seven (50.9%) preterm infants born at <33 weeks of gestation who were diagnosed with congenital hypothyroidism had delayed TSH elevation and would not have been detected on first newborn screen. Twelve of these infants (40.7%) with delayed TSH elevation had decompensated hypothyroidism at diagnosis (free thyroxine [FT4] <10 pmol/L), and 4 had severe congenital hypothyroidism (FT4 <5.5 pmol/L) at diagnosis. If screening had been repeated only at 2 weeks of life, 13 infants (48%) with delayed TSH elevation would not have been identified. Of the 27 infants with delayed TSH elevation, 6 (22%) have permanent congenital hypothyroidism, and another 12 will be reevaluated at age 3 years. Repeat screening for congenital hypothyroidism in preterm infants is necessary to avoid missing cases of congenital hypothyroidism with delayed TSH elevation. Repeat screening once at 2 weeks of life will miss infants with delayed TSH elevation and decompensated permanent congenital hypothyroidism.

Incidence and Risk Factor of Permanent Hypothyroidism in Preterm Infants

Background: To investigate the incidence and risk factors of permanent hypothyroidism in premature infants diagnosed with congenital hypothyroidism. Methods: A retrospective review of medical records of preterm infants was performed between March 2010 and December 2013. We included infants who were treated with thyroxine after being diagnosed with congenital hypothyroidism and persistent hyperthyrotropinemia. Exclusion criteria included an infants who were lost to follow up or earlier discontinuation of thyroxine medication and had proven permanent hypothyroidism. We performed trial offtherapy at 36 months of age. Results: A total of 49 infants were eligible for trial off-therapy at age 3 years. Permanent and transient hypothyroidism was diagnosed in 12 and 37 infants, respectively. Persistent hypothyroidism was more frequent in the infants with high TSH and low FT4 levels at initial screening and high incidence in abnormalities in thyroid imaging work-ups and positive anti-thyroid antibodies. Moreover, the average thyroxine dosage during follow-up was significantly higher in infants with persistent hypothyroidism (p<0.05). Conclusion: Thyroid dysfunction is common in preterm infants, and nearly 80% of infants showed transient hypothyroidism. Therefore, if there is no other risk factor for permanent hypothyroidism, it is possible to consider an earlier trail off- therapy for preterm infants.

Perinatal Factors Associated with the Preterm Thyroid Screening Test

st meconium passage time, respiratory distress syndrome and apnea on thyroid hormone levels were assessed by Mann-Whitney U-test and multiple linear regression analysis. Results: With advancing gestational age, T3 and fT4 displayed a tendency to increase. FT4 showed a positive correlation pattern with antenatal steroid therapy, corrected gestational age at examination and a negative correlation pattern with 1st meconium passage time and apnea (P<0.05). TSH displayed a positive correlation pattern with 1st meconium passage time, 5-minute Apgar score and a negative correlation pattern with sampling age (P<0.05). Conclusion: In the preterm period, both fT4 and TSH seems to correlate significantly with various perinatal factors and clinical presentation. We recommend that early fT4 screening should be included in the screening for hypothyroidism in preterm infants.

Analysis of screening results for congenital hypothyroidism in preterm infants

Objective To discuss the effect of neonatal congenital hypothyroidism(CH)screening in preterm infants. Methods The result of 208 713 cases neonatal congenital hypothyroidism screening in Guangzhou neonatal screening center were analyzed,including 11589 cases preterm infant and 197 124 cases of full term.The difference of screening positive rate and incidence between preterm infants and full term infants group were compared and the efficiency of preterm infants congenital hypothyroidism screening were estimated. Results A total of 208 713 newborns were screened and the screening positive rate was 1.39%.123 cases were confirmed positive for CH and the incidence rate was 1/1 697.124 cases were screening positive in preterm infants and the screening positive rate was 1.06%.14 cases were confirmed positive for CH and the incidence rate was 1/828 in preterm infants group.2 771 cases were screening positive in full term infants and the screening positive rate was 1.41%.109 cases were confirmed positive for CH and the incidence rate was 1/1 809 in full term group.The screening positive rate was lower and the incidence rate of preterm infants group(χ2=4.89,P<0.05)was higher than that of the full term infants group(χ2=8.26,P<0.05). Conclusion The incidence rate of congenital hypothyroidism is higher in preterm infants.Neonatal screening is an effective measure for early diagnosis of preterm infants congenital hypothyroidism. Key words: Preterm infants; Hypothyroidism,congenital; Neonatal screening

Evolution of Thyroid Function in Preterm Infants Detected by Screening for Congenital Hypothyroidism

To determine the evolution of congenital hypothyroidism in preterms and the clinical features of permanent forms. We retrospectively evaluated 24 preterm children detected by newborn screening for congenital hypothyroidism: first screening with blood-thyroid stimulating hormone cutoff ≥10 mU/L and second screening with blood-thyroid stimulating hormone cutoff ≥5 mU/L. After the age of 2years, patients with eutopic thyroid had diagnostic reevaluations, including thyroid function testing and thyroid ultrasonography after L-thyroxine therapy withdrawal. The first screening identified 21.7% of patients with thyroid stimulating hormone elevation, and the second screening identified 73.9% of patients. One patient (4.4%) was identified with a third screening test; 21 patients had an eutopic thyroid and 3 patients a thyroid dysgenesis. At reevaluation, 5 patients (23.8%) showed permanent hypothyroidism (serum-thyroid stimulating hormone [s-TSH] >10 mU/L) resulting in the need to reintroduce therapy, 5 patients (23.8%) showed persistent hyperthyrotropinemia (s-TSH 5-10 mU/L), and 11 infants (52.4%) transient hypothyroidism (s-TSH <5 mU/L). The main clinical features of patients affected by permanent hypothyroidism were 1 case of assisted reproduction, 2 twins, 2 small for gestational age, 1 maternal thyroiditis, and 2 patients with malformations/syndromes. Premature birth is a significant risk for congenital hypothyroidism with eutopic thyroid. In preterm infants, the evolution of congenital hypothyroidism remains difficult to predict. Our data emphasizes the high incidence of transient hypothyroidism in preterm infants, and the importance of diagnostic reevaluation to determine the definitive diagnosis.

A Case of Congenital Hypothyroidism in a Preterm Infant Presenting with Meconium Obstruction

Many infants with congenital hypothyroidism have few or no clinical manifestations at birth. In preterm infants, discovering related signs and symptoms of congenital hypothyroidism is even more difficult, despite the higher incidence of transient thyroid function abnormalities. Therefore, these patients need to be closely monitored during the early neonatal period. We report a case of a very low birth weight infant presenting with meconium obstruction concurrent with congenital hypothyroidism in the early neonatal period. Unless diagnosed and treated appropriately, meconium obstruction of prematurity may lead to feeding intolerance, intestinal perforation, necrotizing enterocolitis, and sepsis. It is important for medical caregivers to under­ stand that meconium obstruction can be an early sign of congenital hypothyroidism in preterm infants with abdominal distension.

Permanent and transient congenital hypothyroidism in full-term and preterm born infants

Congenital hypothyroidism (CH) is one of the most common endocrine disorders in the infant population. It is also one of the most important causes of foreseeable brain damage and severe mental impairment. Current views on CH pathogenesis, screening schema and treatment standards have been presented. Also outlined have been the newest reports on the impact on CH epidemiology and classification generated by the introduction of low TSH cut-off (6 mU/l).The use of low TSH cut-off allowed the detection of an unsuspected number of children with neonatal hypothyroidism, evolving in mild permanent thyroid dysfunction later in life. Constantly growing, especially in developed countries, number of preterm infants is a separate group of children, mainly with transient fluctuations in thyroid function. Thyroid gland function develops and matures during fetal life, with production of serum thyroxine (T4) beginning around 12 weeks gestation and increasing to term. Infants born prior to term have lower cord serum T4 concentrations which correlate with gestational age or/and birth weight. This is partially a result of lower thyroxine-binding globulin (TBG) concentrations. The cord serum free thyroxine (FT4) concentrations also correlate with gestational age, but they are not proportionately as low as cord T4 concentration. Preterm infants have a postnatal thyrotropin (TSH) surge and rise in serum T4 and triiodothyronine (T3), which is qualitatively similar to, but quantitatively smaller than term infants. In contrast to term infants, preterm infants often experience a fall in serum T4 and T3 in the first week of life to below birth levels. This drop appears to be the result of many factors, including nutritional problems and decreased hepatic TBG production, immaturity of hypothalamic-pituitary control of the thyroid gland, immaturity of the thyroid gland itself, and increased tissue utilization of T4. Several studies have correlated different measures of morbidity and mortality in the preterm infant with lower serum T4 concentrations. This has led to speculation that T4 treatment might be beneficial in improving these complications of prematurity, in particular the neurological outcome. Latest studies do not confirm that hypothyroidism in preterm infants is for them harmless. Many factors, however, influence mental development of those children. Thus, treatment strategies, including thyroid hormone substitution, should consider both the etiology of the hypothyroidism and the impact of aforementioned factors. There is no “hard evidence” to support introducing thyroid hormone supplementation in preterm infants as a rule.

Transient Hypothyroidism in Premature Infants After Short-term Topical Iodine Exposure: An Avoidable Risk?

Studies in preterm infants have shown that prolonged treatment with topical iodine (multiple doses, often over multiple days) can transiently suppress thyroid function. However, it is uncertain if topical iodine exposure for very short periods of time can cause significant changes in thyroid function. We report two cases of transient hypothyroidism in preterm infants after short-term exposure to topical iodine during surgical preparation, and review their clinical and laboratory findings before and after iodine exposure. We conclude that premature infants are at risk of developing transient hypothyroidism in response to a single, short-term exposure to topical iodine, even in iodine-sufficient geographical areas. We advise monitoring of thyroid function in these infants after iodine exposure, as treatment with levothyroxine may be needed for a limited duration to prevent the sequelae of untreated hypothyroidism. Consideration of using alternative cleansing agents is also advised.

Analysis and treatment on transient hypothyroidism in preterm infants

Objective To explore the thyroid function and curative effect with thyroid hormone supplementation in premature infants.Methods Serm thyroid-stimulating hormone(TSH),total thyroxine (TT4),free thyroxine(FT4),total triodothyrorine(TT3) and free triodothyrorine(FT3) were detected in 165 premature infants.Premature infants with low TT4 and low FT4 were divided into Levothyroxine group and control group according to clinical symptom; premature infants with low TT3 were randomized into Levothyroxine group and control group.Levothyroxine group received Levothyroxine,TSH,TT4,FT4,TT3 and FT3 were detected once a week.Results ①The thyroid function in the premature infants was transiently low.The shorter the gestational age,the lower the thyroid function.The incidence rate of 28 ～ 30 weeks of gestational age,30 ～ 32 weeks of gestational age,32 ～ 34 weeks of gestational age and 34 ～ 36 weeks of gestational age were 77.27％,75％,39.47％ and 32.47％ respectively.② symptom disappeared after Levothyroxine supplementation in premature infants with low TT4 and low FT4.Time of reaching normal range of the thyroid hormone in Levothyroxine group was significantly shorter than that of control group.The normal rate of serum concentrations of FT4,T4 on the 14th day after birth in Levothyroxine group was 100％,That in control group was 44.4％.(P =0.00).③ Time of reaching normal range of the thyroid hormone was not significantly different between Levothyroxine group with low TT3 and control group with low TT3.The normal rate of serum concentrations of TSH,T3 on the 28th day after birth in Levothyroxine group was 15％,while that in control group was 10％ (P=1.00).Conclusion The thyroid function in the premature infants is transiently low.The shorter the gestational age,the lower the thyroid function.Thyroid hormone replacement therapy in premature infants with a symptom of transient hypothyroxinemia is useful. Key words: Premature infants; Thyroid function; Transient hypothyroidism

Permanent and transient congenital hypothyroidism in preterm infants

Transient fluctuations in thyroid function are well recognized in preterm infants. We wanted to assess TSH variation in babies with transient and permanent congenital hypothyroidism (CHT). Whole bloodspot TSH data in preterm infants (<35 weeks; 2005-2010) were assessed, and infants with bloodspot TSH values >6 mU/L identified. Permanent CHT was defined as a requirement for thyroxine beyond 3 years of age. A first TSH sample was obtained from 5518 infants (median gestational age, 32 w; range, 22-35), with a second sample obtained from 5134 infants (median gestational age, 32 w; range, 22-35). Five infants had raised TSH concentrations on both occasions. Three of the five infants had a serum TSH >80 mU/L on second screen but two came off thyroxine beyond 3 years of age. All preterm babies with permanent or transient hypothyroidism were detected by the first TSH cut-off of 6 mU/L. Only one infant with a birth weight <1500 g remains on thyroxine treatment beyond 2 years of age. The incidence of permanent CHT in preterm infants is similar to term infants. Profound abnormalities of thyroid function can occur in preterm babies with transient hypothyroidism but both categories of hypothyroidism can be detected by a 'once-only' TSH screening strategy with a relatively low cut-off.

Hypothyroidism in preterm infants following normal screening

Congenital hypothyroidism is screened for in the UK using blood spot thyroid-stimulating hormone (TSH) screening at 5-8 d of age. Although standards are set by the UK Newborn Screening Programme Centre, there are variations in TSH cut-offs used. The introduction of repeat screening of preterm babies at 36 weeks' gestational age in 2005 was controversial in its utility and timing. Two cases of preterm babies are presented, who had normal blood spot TSH values on the first test and who became screen positive when re-tested at term. The first with Trisomy 21 was born at 29 + 6 weeks with an initial blood spot TSH of 3.3 mU/L rising to 263 mU/L at term-corrected gestational age (plasma TSH 476.5 mU/L). The second was born at 24 + 6 weeks' gestational age and on day 7, the heel prick blood spot TSH was <2 mU/L, rising to 6.4 mU/L at 36 weeks corrected gestational age. After a barium enema, the plasma TSH increased to 66.6 mU/L with a free thyroxine of 7.6 pmol/L at day 101. Both cases were treated with thyroxine until death due to complications of prematurity. These cases illustrate the difficulties in screening for congenital hypothyroidism in preterm infants, due to the immaturity of the hypothalamo-pituitary-thyroid axis, and the effect of intercurrent illness and drugs on thyroid function. Despite a reassuring published review of 2200 preterm infants, these cases suggest that it may be unwise not to re-screen ex-preterm infants for congenital hypothyroidism at term.

Subclinical Hypothyroidism in Korean Preterm Infants Associated with High Levels of Iodine in Breast Milk

The dietary iodine intake of lactating women has been reported to be high in Korea. The aim of this study was to assess iodine balance and to determine its relationship with thyroid function in preterm infants. Thyroid functions of preterm infants born at 34 wk gestation or less were evaluated in the first (n = 31) and third (n = 19) weeks. Mothers' breast milk (BM) and random urine samples of infants were taken on the same days for thyroid function tests. Iodine concentrations in BM were very high (198-8484 microg/liter), and one third of the infants had an iodine intake of more than 100 microg/kg per day at the third week after birth (excessive iodine intake group). At that time, the levels of TSH were positively correlated with urinary iodine (r = 0.622; P = 0.004). The frequencies of subclinical hypothyroidism were high in the excessive iodine intake group at the third and sixth weeks. The estimated daily iodine intake at the third week (51.2 +/- 45.5 vs. 149.0 +/- 103.8 microg/kg per day; P = 0.033), urinary iodine at the third week (913.2 +/- 1179.7 vs. 1651.3 +/- 1135.2 microg/liter; P = 0.051), and estimated daily iodine intake at the sixth week (32.8 +/- 35.5 vs. 92.1 +/- 51.2 microg/kg per day; P = 0.032) were significantly higher in infants with subclinical hypothyroidism than in controls. Excessive iodine intake from BM contributed to subclinical hypothyroidism in these preterm Korean infants.

Repeat testing for congenital hypothyroidism in preterm infants is unnecessary with an appropriate thyroid stimulating hormone threshold

Background:Revised UK neonatal screening guidelines recommend that a second blood sample for assay of thyroid stimulating hormone (TSH) be taken when preterm infants reach a postmenstrual age of 36 weeks.Objective:To...