Journal of Perinatology (2015), 1–4 © 2015 Nature America, Inc. All rights reserved 0743-8346/15 www.nature.com/jp
ORIGINAL ARTICLE
Response to thyrotropin-releasing hormone stimulation tests in preterm infants with transient hypothyroxinemia of prematurity A Yamamoto, M Kawai, K Iwanaga, T Matsukura, F Niwa, T Hasegawa and T Heike OBJECTIVE: Whether hormone supplementation is necessary for infants with transient hypothyroxinemia of prematurity (THOP) remains controversial, and further analysis of the hypothalamus–pituitary–thyroid axis of infants with THOP is necessary. STUDY DESIGN: Thyrotropin-releasing hormone (TRH) stimulation tests were performed at 2 weeks of age in 50 infants with a gestational age of 30 weeks or less, and the data were analyzed retrospectively. RESULT: Subjects were divided into three groups; group A consisted of euthyroid infants, group B consisted of infants with THOP and group C consisted of hypothyroid infants. The basal and peak thyroid-stimulating hormone level of group C in response to TRH stimulation tests was significantly higher than the others, but no differences were observed between groups A and B. CONCLUSION: The response of infants with THOP to the TRH stimulation test was not different from that of euthyroid infants, which suggested that their hypothalamic–pituitary–thyroid axis was appropriately regulated in infants with THOP. Journal of Perinatology advance online publication, 25 June 2015; doi:10.1038/jp.2015.67
INTRODUCTION Transient hypothyroxinemia of prematurity (THOP) is a common problem for very low-birth-weight (VLBW) infants.1,2 Although trials to treat infants with THOP had been performed, no definite improvement has been reported due to thyroid hormone supplementation; therefore, the effectiveness of thyroid hormone supplementation in infants with THOP remains controversial.3–6 To prove the effectiveness of supplemental therapy, randomized controlled trials still need to be conducted.7 However, van Wassenaer-Leeimhuis et al.8 reported that no positive effects were found in relation to thyroid hormone treatment in a recent report. Some physicians consider that levothyroxine sodium (LT4) supplementation is necessary due to an immature hypothalamic– pituitary–thyroid (HPT) axis in infants, which results in the inability to produce sufficient thyroid-stimulating hormone (TSH) levels even if they have hypothyroxinemia and require LT4 supplementation therapy. However, we previously reported that most extremely premature infants exhibited a prompt response to the TRH stimulation test at ~ 2 weeks of age.9 On the other hand, circulatory dysfunctions associated with its administration to VLBW infants have recently been reported.10–13 The findings suggest that the administration of levothyroxine to VLBW infants may have unfavorable effects. On the basis of these findings, we considered it important to evaluate the HPT axis of infants with THOP. The TRH stimulation test was performed at ~ 2 weeks of age in the present study to evaluate the HPT axis and thyroid function. METHODS Subjects VLBW infants who were born at a gestational age (GA) of o 30 weeks, were admitted from an early age to the neonatal intensive-care unit (NICU) of Kyoto University Hospital, and were followed to full GA between January
2008 and December 2012 were included in this study. Infants with maternal thyroid diseases, chromosomal abnormalities and other suspicious cases of hypopituitarism (including ambiguous genitalia, hypoglycemia due to pituitary deficits and mid-line anomalies) were excluded from this study. Ethics approval was obtained from the Kyoto University Graduate School and Faculty of Medicine Ethics Committee, and informed parental consent was obtained before each procedure.
Serum free thyroxine (FT4) and TSH measurements and the TRH stimulation test We measured serum FT4 and TSH levels in ~ 2-week-old VLBW infants. We generally did not administer LT4 to infants with low FT4 and normal TSH levels (THOP), but administered 5 μg kg − 1 LT4 to infants with elevated TSH levels (TSH415 mU l − 1). As infants with low FT4 levels and delayed elevations in TSH levels may have been missed in the initial screening, serum FT4 and TSH measurements were repeated at 1- and 2-week intervals in infants whose TSH levels were lower than 15 mU l − 1 until they approached full GA. FT4 and TSH were measured by ECLIA (Roche Diagnostics, Tokyo, Japan). As well as monitoring FT4 and TSH, we conducted the TRH stimulation test at ~ 2 weeks of age. The TRH stimulation test is performed by a simple method; 7 μg kg − 1 TRH (Tanabe Mitsubishi Pharmaceutical Company, Osaka, Japan) is injected via a peripheral venous line and serum is collected before and 30 min after the injection.9,14
Statistical analysis The Mann–Whitney U-test and linear regression were used to compare continuous variables, and the χ2-test was used to analyze categorical data. Po0.05 was considered significant. All statistical analyses were performed with STATA release 13 for Windows (Stata Corp LP, College Station, TX, USA).
RESULTS Patient profiles A total of 108 infants were born at a GA of o 30 weeks and admitted from an early age to the NICU of Kyoto University
Department of Pediatrics, Graduate School of Medicine, Kyoto University, Kyoto, Japan. Correspondence: Dr A Yamamoto, Department of Pediatrics, Graduate School of Medicine, Kyoto University, 54 Kawaramachi, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan. E-mail: [email protected] Received 21 October 2014; revised 12 March 2015; accepted 5 May 2015
TRH tests in preterm infants with hypothyroxinemia A Yamamoto et al
2 Hospital between January 2008 and December 2012. Three infants died early for their age, 22 infants were transferred to nearby hospitals after their condition had been stabilized and 4 infants were excluded because their mothers had thyroid diseases. Twenty-nine infants were also excluded because informed consent was not obtained from their parents. Therefore, a total of 50 infants were recruited for this study. None were reported to have hyperthyrotropinemia by mass screening of TSH measurements (cutoff value of 10 mU l − 1), which was performed at 5 days of age. Serum FT4 and TSH levels were evaluated at a postnatal age of ~ 2 weeks of age. Infants were divided into three groups; group A consisted of 29-euthyroid infants with normal FT4 (FT4 ⩾ 0.8 ng dl − 1) and normal TSH (TSH ⩽ 15 mU l − 1), group B consisted of 15 infants with THOP with low FT4 (FT4 o 0.8 ng dl − 1) and normal TSH and group C consisted of six-hypothyroid infants with elevated TSH (TSH415 mU l − 1). Table 1 shows the profile of infants in each group. Briefly, the GA and birth weight (BW) were significantly different between infants in group B and those in group A. However, no significant differences were observed in the other parameters. Basal FT4 levels at ~ 2 weeks of age The basal FT4 levels of groups A, B and C were 1.11 ± 0.20, 0.61 ± 0.16 and 0.87 ± 0.34 ng dl − 1, respectively. Basal FT4 levels were significantly lower in group B than in group A (P o 0.0001); however, no significant difference was observed in basal FT4 levels between groups A and C (P = 0.0658). TSH levels in response to the TRH stimulation test at ~ 2 weeks of age The basal TSH levels of groups A, B and C were 6.1 ± 3.5, 4.8 ± 3.2, and 27.6 ± 10.2 mU l − 1, respectively (Table 2). Basal TSH levels were significantly higher in group C than in the other groups (P o 0.001). In addition, the peak TSH levels of group C were significantly higher than those of group A and group B,
Table 1.
Subject profiles Group A (n = 29) Group B (n = 15) Group C (n = 6)
GA (weeks) BW (grams) Gender (male) Apgar at 1 min Apgar at 5 min Antenatal glucocorticoid CAM SGA
27.7 ± 1.6 976.4 ± 282.1 20 (69.0%) 5.1 ± 2.7 7.1 ± 2.3 22 (75.9%)
26.0 ± 1.5a 706.3 ± 159.3a 8 (53.3%) 4.0 ± 2.2 6.3 ± 2.2 10 (66.7%)
27.2 ± 2.0 772.7 ± 114.5 4 (66.7%) 3.8 ± 1.9 7.0 ± 1.7 3 (50.0%)
10 (34.5%) 4 (13.8%)
7 (46.7%) 4 (26.7%)
4 (66.7%) 3 (50.0%)
Abbreviations: BW, body weight; CAM, chorioamnionitis; GA, gestational age; SGA, small for gestational age. aSignificantly different from group A (Po0.05).
Table 2.
Parameters related to the TRH stimulation test Group A (n = 29) Group B (n = 15) Group C (n = 6) −1
Basal TSH (IU ml ) Peak TSH (IU ml − 1) TSH Δ (IU ml − 1) Basal FT4 (ng dl − 1)
6.1 ± 3.5 31.5 ± 12.7 25.4 ± 10.2 1.1 ± 0.2
4.8 ± 3.2 33.1 ± 14.3 28.3 ± 13.3 0.6 ± 0.2a
27.6 ± 10.2a 70.9 ± 28.2a 43.3 ± 18.3a 0.9 ± 0.3
Abbreviations: TRH, thyrotropin-releasing hormone; TSH, thyroidstimulating hormone. aSignificantly different from group A (Po 0.05).
Journal of Perinatology (2015), 1 – 4
respectively (P o0.01). In contrast, no significant differences were observed in delta and peak TSH levels between groups A and B (P = 0.72 and 0.58, respectively). These results indicated that not only basal TSH levels but also the response to the TRH stimulation test were not different between groups A and B. Relationship between the TRH test and GA at birth As the GA of group B was shorter than that of group A, we evaluated the correlation between thyroid parameters and GA. As shown in Figure 1, FT4 levels were positively correlated with GA (r = 0.44, P = 0.003), which is consistent with the high frequency of THOP in infants with a shorter GA. In contrast, basal TSH levels as well as the response of TSH to the TRH stimulation test were not correlated with GA (P = 0.29 and 0.97, respectively). These results indicated that the response of infants in group B to the TRH stimulation test was not different from that in group A. Transition of FT4 levels in infants of THOP (group B) FT4 levels of infants with group B were increased to the normal range (0.8 ng dl − 1 or higher) spontaneously. The date we confirmed the normalization of FT4 levels was at 33.8 ± 14.9 days of age, ranging from 22 to 79 days of age. Clinical course of the subjects The clinical features of the subjects who participated in the present study are listed in Table 3. Gastrointestinal (GI) complications, such as necrotizing enterocolitis (NEC), meconium-related ileus and perforations in the GI tract, were more common in group B. On the basis of these GI complications, the prevalence of feeding difficulties was higher in infants in group B. DISCUSSION For preterm infants with THOP, several reports have demonstrated that low FT4 levels are strongly associated with poor neurodevelopmental outcomes1,15–23 and many trials to treat infants with THOP had been performed, but no definite improvement has been reported. On the basis of these results, we considered that further understanding of the HPT axis of infants with THOP is necessary. In 2012, Niwa et al.9 reported that most of the preterm infants showed significant response to TRH stimulation tests at ~ 2 weeks of age. In the current study, we analyzed the difference of response to TRH tests among three groups; group A consisted of euthyroid infants, group B consisted of infants with THOP and group C consisted of hypothyroid infants with elevated TSH. As a result, infants with group C had significantly higher basal and peak TSH levels, but there were no differences between group A and group B. For the etiology of THOP, several factors were postulated: detachment from the placenta, excess or deficiency of iodide, use of drugs that suppress TSH secretion, such as glucocorticoid and dopamine, deficiency of hypothalamic TRH in the preterm infants and non-thyroidal illness. Regardless of the cause of low FT4 levels, TSH levels should increase if the HPT axis is properly regulated. Therefore, detachment from the placenta or excess or deficiency of iodide cannot explain the reason for the normal levels of serum TSH. Considering that dopamine or glucocorticoid might suppress HPT axis, we investigated the effects of these drugs. To test its possibility, we reviewed the patients’ record but found no differences in the rate of administering dopamine or glucocorticoids among the three groups (data not shown). We therefore concluded that the effects of such drugs cannot be a major factor. The concept of hypothalamic TRH deficiency was postulated in the 1970s24,25 It was based on animal models26 and the data obtained from human fetus,27 but there is no evidence in © 2015 Nature America, Inc.
TRH tests in preterm infants with hypothyroxinemia A Yamamoto et al
3 r=0.44 p=0.003
GA-FT4
GA-TSH pre
r= - 0.006 p=0.97
GA-TSHdelta
15
1.5
1
0.5
0
TSHdelta (mU/l)
50 TSH pre (mU/l)
FT4 (ng/dl)
r=0.16 p=0.29
10
5
0 22
24
26
28
30
40 30 20 10 0
22
24
GA
26
28
30
22
24
26
28
30
GA
GA
Figure 1. Relationship between gestational age (GA) and thyroid functions. FT4 levels were positively correlated with GA (r = 0.44, P = 0.003). Basal TSH levels (r = 0.16, P = 0.29) and delta TSH (peak minus the basal TSH level) (r = − 0.006, P = 0.97) were not correlated with GA.
Table 3.
Clinical features
Milk volume at 2 weeks of age (ml) Postnatal days at full feeding (days) RDS (%) Meconium-related ileus, NEC or perforations of GI tract CLD (%) Death (%)
Group A (n = 29)
Group B (n = 15)
Group C (n = 6)
98.4 ± 46.7 16.5 ± 10.6 17/29 (58.6%) 2/29 (6.7%) 17/29 (58.6%) 1/29 (3.4%)
78.8 ± 47.3 23.1 ± 12.1 11/15 (73.3%) 5/15 (33.3%) 13/15 (86.7%) 2/15 (13.3%)
100.0 ± 15.1 22.0 ± 22.2 3/6 (50.0%) 2/6 (33.3%) 5/6 (83.3%) 0/6 (0%)
Abbreviations: CLD, chronic lung disease; GI, gastrointestinal; NEC, necrotizing enterocolitis; RDS, respiratory distress syndrome.
human preterm infants. For the assessment of HPT axis, one cannot measure human hypothalamic TRH directly for the preterm infants after birth. Owing to these, TRH stimulation tests are considered to be an important tool. If hypothalamic TRH deficiency is the main cause of THOP, the basal TSH levels should be low and the secretion of TSH in response to TRH might be exaggerated. But we found no differences in the basal levels of TSH between infants with THOP (group B) and euthyroid infants (group A). In addition, there were no differences in the response of TSH (delta TSH) between these two groups (Table 2). These findings indicated that the hypothalamic TRH deficiency is unlikely to be the main cause for the mechanisms of THOP. In this study, we confirmed that the low FT4 levels of infants with THOP were transient, and that they entered the normal range spontaneously. In addition, complications associated with the GI tract, such as necrotizing enterocolitis, meconium-related ileus and perforations in the GI tract, were more common in infants with THOP. Timing for the normalization of FT4 levels was matched to the resolution of these complications. On the basis of these observations, such complications were considered to have disturbed enteral nutrition so that infants with THOP appear to have more risk factors for poor nutrition, which might cause nonthyroidal illnesses. Increasing the metabolic rates of infants with non-thyroidal illnesses by administering LT4 as well as those of infants with subclinical hyperthyroidism by administering levothyroxine may potentially be harmful.28,29 In addition, the administration of levothyroxine to premature infants was considered to be as safe as that to mature infants; however, circulatory dysfunctions associated with the administration of levothyroxine to VLBW infants have recently been reported.10–13 On the basis of these findings, we considered that administration of levothyroxine to VLBW infants with THOP should be paid more attention. A major limitation of this study is the small number of subjects examined, because of which we cannot confirm whether infants with THOP need to be supplemented with LT4. Therefore, a powerful RCT needs to be conducted in the future.7,8 However, © 2015 Nature America, Inc.
our results on the HPT axis in VLBW infants born at a GA of o30 weeks provide an important insight into THOP. CONFLICT OF INTEREST The authors declare no conflict of interest.
REFERENCES 1 Reuss ML, Leviton A, Paneth N, Susser M. Thyroxine values from newborn screening of 919 infants born before 29 weeks’ gestation. Am J Public Health 1997; 87(10): 1693–1697. 2 Sureka Bollepalli SRR. Disorders of the thyroid gland. In: Christine A, Gleason SUD (eds) Avery’s Disease of the Newborn. 9th edn, Elsevier: Philadelphia, PA, USA 2012, pp 1307–1319. 3 Rapaport R, Rose SR, Freemark M. Hypothyroxinemia in the preterm infant: the benefits and risks of thyroxine treatment. J Pediatr 2001; 139(2): 182–188. 4 van Wassenaer AG, Kok JH, de Vijlder JJ, Briet JM, Smit BJ, Tamminga P et al. Effects of thyroxine supplementation on neurologic development in infants born at less than 30 weeks’ gestation. N Engl J Med 1997; 336(1): 21–26. 5 Osborn DA, Hunt RW. Postnatal thyroid hormones for preterm infants with transient hypothyroxinaemia. Cochrane Database Syst Rev 2007; (1): CD005945. 6 Briet JM, van Wassenaer AG, Dekker FW, de Vijlder JJ, van Baar A, Kok JH. Neonatal thyroxine supplementation in very preterm children: developmental outcome evaluated at early school age. Pediatrics 2001; 107(4): 712–718. 7 La Gamma EF, van Wassenaer AG, Ares S, Golombek SG, Kok JH, Quero J et al. Phase 1 trial of 4 thyroid hormone regimens for transient hypothyroxinemia in neonates of o 28 weeks’ gestation. Pediatrics 2009; 124(2): e258–e268. 8 van Wassenaer-Leemhuis A, Ares S, Golombek S, Kok J, Paneth N, Kase J et al. Thyroid hormone supplementation in preterm infants born before 28 weeks gestational age and neurodevelopmental outcome at age 36 months. Thyroid 2014; 24(7): 1162–1169. 9 Niwa F, Kawai M, Kanazawa H, Iwanaga K, Matsukura T, Hasegawa T et al. Hyperthyrotropinemia at 2 weeks of age indicates thyroid dysfunction and predicts the occurrence of delayed elevation of thyrotropin in very low birth weight infants. Clin Endocrinol (Oxf) 2012; 77(2): 255–261. 10 Okada J, Iwata S, Hirose A, Kanda H, Yoshino M, Maeno Y et al. Levothyroxine replacement therapy and refractory hypotension out of transitional period in preterm infants. Clin Endocrinol (Oxf) 2011; 74(3): 354–364.
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4 11 Kawai M, Kusuda S, Cho K, Horikawa R, Takizawa F, Ono M et al. Nationwide surveillance of circulatory collapse associated with levothyroxine administration in very-low-birthweight infants in Japan. Pediatr Int 2012; 54(2): 177–181. 12 Takizawa F, Kashimada K, Enomoto K, Miyai K, Ono M, Asada G et al. Two preterm infants with late onset circulatory collapse induced by levothyroxine sodium. Pediatr Int 2010; 52(3): e154–e157. 13 Yagasaki H, Kobayashi K, Nemoto A, Naito A, Sugita K, Ohyama K. Late-onset circulatory dysfunction after thyroid hormone treatment in an extremely low birth weight infant. J Pediatr Endocrinol Metab 2010; 23(1–2): 153–158. 14 Rapaport R, Sills I, Patel U, Oppenheimer E, Skuza K, Horlick M et al. Thyrotropinreleasing hormone stimulation tests in infants. J Clin Endocrinol Metab 1993; 77(4): 889–894. 15 de Zegher F, Pernasetti F, Vanhole C, Devlieger H, Van den Berghe G, Martial JA. The prenatal role of thyroid hormone evidenced by fetomaternal Pit-1 deficiency. J Clin Endocrinol Metab 1995; 80(11): 3127–3130. 16 Vulsma T, Gons MH, de Vijlder JJ. Maternal-fetal transfer of thyroxine in congenital hypothyroidism due to a total organification defect or thyroid agenesis. N Engl J Med 1989; 321(1): 13–16. 17 Haddow JE, Palomaki GE, Allan WC, Williams JR, Knight GJ, Gagnon J et al. Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child. N Engl J Med 1999; 341(8): 549–555. 18 van Wassenaer AG, Kok JH, Dekker FW, de Vijlder JJ. Thyroid function in very preterm infants: influences of gestational age and disease. Pediatr Res 1997; 42(5): 604–609. 19 Den Ouden AL, Kok JH, Verkerk PH, Brand R, Verloove-Vanhorick SP. The relation between neonatal thyroxine levels and neurodevelopmental outcome at age 5 and 9 years in a national cohort of very preterm and/or very low birth weight infants. Pediatr Res 1996; 39(1): 142–145.
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20 Ares S, Quero J, Diez J, Morreale de Escobar G. Neurodevelopment of preterm infants born at 28 to 36 weeks of gestational age: the role of hypothyroxinemia and long-term outcome at 4 years. J Pediatr Endocrinol Metab 2011; 24(11-12): 897–902. 21 Leviton A, Paneth N, Reuss ML, Susser M, Allred EN, Dammann O et al. Hypothyroxinemia of prematurity and the risk of cerebral white matter damage. J Pediatr 1999; 134(6): 706–711. 22 Lucas A, Morley R, Fewtrell MS. Low triiodothyronine concentration in preterm infants and subsequent intelligence quotient (IQ) at 8 year follow up. BMJ 1996; 312(7039): 1132–1133; discussion 1133-1134. 23 Meijer WJ, Verloove-Vanhorick SP, Brand R, van den Brande JL. Transient hypothyroxinaemia associated with developmental delay in very preterm infants. Arch Dis Child 1992; 67(7): 944–947. 24 Hadeed AJ, Asay LD, Klein AH, Fisher DA. Significance of transient postnatal hypothyroxinemia in premature infants with and without respiratory distress syndrome. Pediatrics 1981; 68(4): 494–498. 25 Cuestas RA, Engel RR. Thyroid function in preterm infants with respiratory distress syndrome. J Pediatr 1979; 94(4): 643–646. 26 Polk DH, Reviczky A, Lam RW, Fisher DA. Thyrotropin-releasing hormone in ovine fetus: ontogeny and effect of thyroid hormone. Am J Physiol 1991; 260(1 Pt 1): E53–E58. 27 Koivusalo F. Evidence of thyrotropin-releasing hormone activity in autopsy pancreata from newborns. J Clin Endocrinol Metab 1981; 53(4): 734–736. 28 Kaptein EM, Beale E, Chan LS. Thyroid hormone therapy for obesity and nonthyroidal illnesses: a systematic review. J Clin Endocrinol Metab 2009; 94(10): 3663–3675. 29 Biondi B, Cooper DS. The clinical significance of subclinical thyroid dysfunction. Endocr Rev 2008; 29(1): 76–131.
© 2015 Nature America, Inc.
ORIGINAL ARTICLE
Response to thyrotropin-releasing hormone stimulation tests in preterm infants with transient hypothyroxinemia of prematurity A Yamamoto, M Kawai, K Iwanaga, T Matsukura, F Niwa, T Hasegawa and T Heike OBJECTIVE: Whether hormone supplementation is necessary for infants with transient hypothyroxinemia of prematurity (THOP) remains controversial, and further analysis of the hypothalamus–pituitary–thyroid axis of infants with THOP is necessary. STUDY DESIGN: Thyrotropin-releasing hormone (TRH) stimulation tests were performed at 2 weeks of age in 50 infants with a gestational age of 30 weeks or less, and the data were analyzed retrospectively. RESULT: Subjects were divided into three groups; group A consisted of euthyroid infants, group B consisted of infants with THOP and group C consisted of hypothyroid infants. The basal and peak thyroid-stimulating hormone level of group C in response to TRH stimulation tests was significantly higher than the others, but no differences were observed between groups A and B. CONCLUSION: The response of infants with THOP to the TRH stimulation test was not different from that of euthyroid infants, which suggested that their hypothalamic–pituitary–thyroid axis was appropriately regulated in infants with THOP. Journal of Perinatology advance online publication, 25 June 2015; doi:10.1038/jp.2015.67
INTRODUCTION Transient hypothyroxinemia of prematurity (THOP) is a common problem for very low-birth-weight (VLBW) infants.1,2 Although trials to treat infants with THOP had been performed, no definite improvement has been reported due to thyroid hormone supplementation; therefore, the effectiveness of thyroid hormone supplementation in infants with THOP remains controversial.3–6 To prove the effectiveness of supplemental therapy, randomized controlled trials still need to be conducted.7 However, van Wassenaer-Leeimhuis et al.8 reported that no positive effects were found in relation to thyroid hormone treatment in a recent report. Some physicians consider that levothyroxine sodium (LT4) supplementation is necessary due to an immature hypothalamic– pituitary–thyroid (HPT) axis in infants, which results in the inability to produce sufficient thyroid-stimulating hormone (TSH) levels even if they have hypothyroxinemia and require LT4 supplementation therapy. However, we previously reported that most extremely premature infants exhibited a prompt response to the TRH stimulation test at ~ 2 weeks of age.9 On the other hand, circulatory dysfunctions associated with its administration to VLBW infants have recently been reported.10–13 The findings suggest that the administration of levothyroxine to VLBW infants may have unfavorable effects. On the basis of these findings, we considered it important to evaluate the HPT axis of infants with THOP. The TRH stimulation test was performed at ~ 2 weeks of age in the present study to evaluate the HPT axis and thyroid function. METHODS Subjects VLBW infants who were born at a gestational age (GA) of o 30 weeks, were admitted from an early age to the neonatal intensive-care unit (NICU) of Kyoto University Hospital, and were followed to full GA between January
2008 and December 2012 were included in this study. Infants with maternal thyroid diseases, chromosomal abnormalities and other suspicious cases of hypopituitarism (including ambiguous genitalia, hypoglycemia due to pituitary deficits and mid-line anomalies) were excluded from this study. Ethics approval was obtained from the Kyoto University Graduate School and Faculty of Medicine Ethics Committee, and informed parental consent was obtained before each procedure.
Serum free thyroxine (FT4) and TSH measurements and the TRH stimulation test We measured serum FT4 and TSH levels in ~ 2-week-old VLBW infants. We generally did not administer LT4 to infants with low FT4 and normal TSH levels (THOP), but administered 5 μg kg − 1 LT4 to infants with elevated TSH levels (TSH415 mU l − 1). As infants with low FT4 levels and delayed elevations in TSH levels may have been missed in the initial screening, serum FT4 and TSH measurements were repeated at 1- and 2-week intervals in infants whose TSH levels were lower than 15 mU l − 1 until they approached full GA. FT4 and TSH were measured by ECLIA (Roche Diagnostics, Tokyo, Japan). As well as monitoring FT4 and TSH, we conducted the TRH stimulation test at ~ 2 weeks of age. The TRH stimulation test is performed by a simple method; 7 μg kg − 1 TRH (Tanabe Mitsubishi Pharmaceutical Company, Osaka, Japan) is injected via a peripheral venous line and serum is collected before and 30 min after the injection.9,14
Statistical analysis The Mann–Whitney U-test and linear regression were used to compare continuous variables, and the χ2-test was used to analyze categorical data. Po0.05 was considered significant. All statistical analyses were performed with STATA release 13 for Windows (Stata Corp LP, College Station, TX, USA).
RESULTS Patient profiles A total of 108 infants were born at a GA of o 30 weeks and admitted from an early age to the NICU of Kyoto University
Department of Pediatrics, Graduate School of Medicine, Kyoto University, Kyoto, Japan. Correspondence: Dr A Yamamoto, Department of Pediatrics, Graduate School of Medicine, Kyoto University, 54 Kawaramachi, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan. E-mail: [email protected] Received 21 October 2014; revised 12 March 2015; accepted 5 May 2015
TRH tests in preterm infants with hypothyroxinemia A Yamamoto et al
2 Hospital between January 2008 and December 2012. Three infants died early for their age, 22 infants were transferred to nearby hospitals after their condition had been stabilized and 4 infants were excluded because their mothers had thyroid diseases. Twenty-nine infants were also excluded because informed consent was not obtained from their parents. Therefore, a total of 50 infants were recruited for this study. None were reported to have hyperthyrotropinemia by mass screening of TSH measurements (cutoff value of 10 mU l − 1), which was performed at 5 days of age. Serum FT4 and TSH levels were evaluated at a postnatal age of ~ 2 weeks of age. Infants were divided into three groups; group A consisted of 29-euthyroid infants with normal FT4 (FT4 ⩾ 0.8 ng dl − 1) and normal TSH (TSH ⩽ 15 mU l − 1), group B consisted of 15 infants with THOP with low FT4 (FT4 o 0.8 ng dl − 1) and normal TSH and group C consisted of six-hypothyroid infants with elevated TSH (TSH415 mU l − 1). Table 1 shows the profile of infants in each group. Briefly, the GA and birth weight (BW) were significantly different between infants in group B and those in group A. However, no significant differences were observed in the other parameters. Basal FT4 levels at ~ 2 weeks of age The basal FT4 levels of groups A, B and C were 1.11 ± 0.20, 0.61 ± 0.16 and 0.87 ± 0.34 ng dl − 1, respectively. Basal FT4 levels were significantly lower in group B than in group A (P o 0.0001); however, no significant difference was observed in basal FT4 levels between groups A and C (P = 0.0658). TSH levels in response to the TRH stimulation test at ~ 2 weeks of age The basal TSH levels of groups A, B and C were 6.1 ± 3.5, 4.8 ± 3.2, and 27.6 ± 10.2 mU l − 1, respectively (Table 2). Basal TSH levels were significantly higher in group C than in the other groups (P o 0.001). In addition, the peak TSH levels of group C were significantly higher than those of group A and group B,
Table 1.
Subject profiles Group A (n = 29) Group B (n = 15) Group C (n = 6)
GA (weeks) BW (grams) Gender (male) Apgar at 1 min Apgar at 5 min Antenatal glucocorticoid CAM SGA
27.7 ± 1.6 976.4 ± 282.1 20 (69.0%) 5.1 ± 2.7 7.1 ± 2.3 22 (75.9%)
26.0 ± 1.5a 706.3 ± 159.3a 8 (53.3%) 4.0 ± 2.2 6.3 ± 2.2 10 (66.7%)
27.2 ± 2.0 772.7 ± 114.5 4 (66.7%) 3.8 ± 1.9 7.0 ± 1.7 3 (50.0%)
10 (34.5%) 4 (13.8%)
7 (46.7%) 4 (26.7%)
4 (66.7%) 3 (50.0%)
Abbreviations: BW, body weight; CAM, chorioamnionitis; GA, gestational age; SGA, small for gestational age. aSignificantly different from group A (Po0.05).
Table 2.
Parameters related to the TRH stimulation test Group A (n = 29) Group B (n = 15) Group C (n = 6) −1
Basal TSH (IU ml ) Peak TSH (IU ml − 1) TSH Δ (IU ml − 1) Basal FT4 (ng dl − 1)
6.1 ± 3.5 31.5 ± 12.7 25.4 ± 10.2 1.1 ± 0.2
4.8 ± 3.2 33.1 ± 14.3 28.3 ± 13.3 0.6 ± 0.2a
27.6 ± 10.2a 70.9 ± 28.2a 43.3 ± 18.3a 0.9 ± 0.3
Abbreviations: TRH, thyrotropin-releasing hormone; TSH, thyroidstimulating hormone. aSignificantly different from group A (Po 0.05).
Journal of Perinatology (2015), 1 – 4
respectively (P o0.01). In contrast, no significant differences were observed in delta and peak TSH levels between groups A and B (P = 0.72 and 0.58, respectively). These results indicated that not only basal TSH levels but also the response to the TRH stimulation test were not different between groups A and B. Relationship between the TRH test and GA at birth As the GA of group B was shorter than that of group A, we evaluated the correlation between thyroid parameters and GA. As shown in Figure 1, FT4 levels were positively correlated with GA (r = 0.44, P = 0.003), which is consistent with the high frequency of THOP in infants with a shorter GA. In contrast, basal TSH levels as well as the response of TSH to the TRH stimulation test were not correlated with GA (P = 0.29 and 0.97, respectively). These results indicated that the response of infants in group B to the TRH stimulation test was not different from that in group A. Transition of FT4 levels in infants of THOP (group B) FT4 levels of infants with group B were increased to the normal range (0.8 ng dl − 1 or higher) spontaneously. The date we confirmed the normalization of FT4 levels was at 33.8 ± 14.9 days of age, ranging from 22 to 79 days of age. Clinical course of the subjects The clinical features of the subjects who participated in the present study are listed in Table 3. Gastrointestinal (GI) complications, such as necrotizing enterocolitis (NEC), meconium-related ileus and perforations in the GI tract, were more common in group B. On the basis of these GI complications, the prevalence of feeding difficulties was higher in infants in group B. DISCUSSION For preterm infants with THOP, several reports have demonstrated that low FT4 levels are strongly associated with poor neurodevelopmental outcomes1,15–23 and many trials to treat infants with THOP had been performed, but no definite improvement has been reported. On the basis of these results, we considered that further understanding of the HPT axis of infants with THOP is necessary. In 2012, Niwa et al.9 reported that most of the preterm infants showed significant response to TRH stimulation tests at ~ 2 weeks of age. In the current study, we analyzed the difference of response to TRH tests among three groups; group A consisted of euthyroid infants, group B consisted of infants with THOP and group C consisted of hypothyroid infants with elevated TSH. As a result, infants with group C had significantly higher basal and peak TSH levels, but there were no differences between group A and group B. For the etiology of THOP, several factors were postulated: detachment from the placenta, excess or deficiency of iodide, use of drugs that suppress TSH secretion, such as glucocorticoid and dopamine, deficiency of hypothalamic TRH in the preterm infants and non-thyroidal illness. Regardless of the cause of low FT4 levels, TSH levels should increase if the HPT axis is properly regulated. Therefore, detachment from the placenta or excess or deficiency of iodide cannot explain the reason for the normal levels of serum TSH. Considering that dopamine or glucocorticoid might suppress HPT axis, we investigated the effects of these drugs. To test its possibility, we reviewed the patients’ record but found no differences in the rate of administering dopamine or glucocorticoids among the three groups (data not shown). We therefore concluded that the effects of such drugs cannot be a major factor. The concept of hypothalamic TRH deficiency was postulated in the 1970s24,25 It was based on animal models26 and the data obtained from human fetus,27 but there is no evidence in © 2015 Nature America, Inc.
TRH tests in preterm infants with hypothyroxinemia A Yamamoto et al
3 r=0.44 p=0.003
GA-FT4
GA-TSH pre
r= - 0.006 p=0.97
GA-TSHdelta
15
1.5
1
0.5
0
TSHdelta (mU/l)
50 TSH pre (mU/l)
FT4 (ng/dl)
r=0.16 p=0.29
10
5
0 22
24
26
28
30
40 30 20 10 0
22
24
GA
26
28
30
22
24
26
28
30
GA
GA
Figure 1. Relationship between gestational age (GA) and thyroid functions. FT4 levels were positively correlated with GA (r = 0.44, P = 0.003). Basal TSH levels (r = 0.16, P = 0.29) and delta TSH (peak minus the basal TSH level) (r = − 0.006, P = 0.97) were not correlated with GA.
Table 3.
Clinical features
Milk volume at 2 weeks of age (ml) Postnatal days at full feeding (days) RDS (%) Meconium-related ileus, NEC or perforations of GI tract CLD (%) Death (%)
Group A (n = 29)
Group B (n = 15)
Group C (n = 6)
98.4 ± 46.7 16.5 ± 10.6 17/29 (58.6%) 2/29 (6.7%) 17/29 (58.6%) 1/29 (3.4%)
78.8 ± 47.3 23.1 ± 12.1 11/15 (73.3%) 5/15 (33.3%) 13/15 (86.7%) 2/15 (13.3%)
100.0 ± 15.1 22.0 ± 22.2 3/6 (50.0%) 2/6 (33.3%) 5/6 (83.3%) 0/6 (0%)
Abbreviations: CLD, chronic lung disease; GI, gastrointestinal; NEC, necrotizing enterocolitis; RDS, respiratory distress syndrome.
human preterm infants. For the assessment of HPT axis, one cannot measure human hypothalamic TRH directly for the preterm infants after birth. Owing to these, TRH stimulation tests are considered to be an important tool. If hypothalamic TRH deficiency is the main cause of THOP, the basal TSH levels should be low and the secretion of TSH in response to TRH might be exaggerated. But we found no differences in the basal levels of TSH between infants with THOP (group B) and euthyroid infants (group A). In addition, there were no differences in the response of TSH (delta TSH) between these two groups (Table 2). These findings indicated that the hypothalamic TRH deficiency is unlikely to be the main cause for the mechanisms of THOP. In this study, we confirmed that the low FT4 levels of infants with THOP were transient, and that they entered the normal range spontaneously. In addition, complications associated with the GI tract, such as necrotizing enterocolitis, meconium-related ileus and perforations in the GI tract, were more common in infants with THOP. Timing for the normalization of FT4 levels was matched to the resolution of these complications. On the basis of these observations, such complications were considered to have disturbed enteral nutrition so that infants with THOP appear to have more risk factors for poor nutrition, which might cause nonthyroidal illnesses. Increasing the metabolic rates of infants with non-thyroidal illnesses by administering LT4 as well as those of infants with subclinical hyperthyroidism by administering levothyroxine may potentially be harmful.28,29 In addition, the administration of levothyroxine to premature infants was considered to be as safe as that to mature infants; however, circulatory dysfunctions associated with the administration of levothyroxine to VLBW infants have recently been reported.10–13 On the basis of these findings, we considered that administration of levothyroxine to VLBW infants with THOP should be paid more attention. A major limitation of this study is the small number of subjects examined, because of which we cannot confirm whether infants with THOP need to be supplemented with LT4. Therefore, a powerful RCT needs to be conducted in the future.7,8 However, © 2015 Nature America, Inc.
our results on the HPT axis in VLBW infants born at a GA of o30 weeks provide an important insight into THOP. CONFLICT OF INTEREST The authors declare no conflict of interest.
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