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Key messages

  • Establishing the maternal thyroid history is essential to determine the need for thyroid function tests (TFT) in neonates.
  • All newborns have thyroid stimulating hormone (TSH) screening for congenital hypothyroidism at 48-72 hours as part of the newborn bloodspot screening test.
  • Apart from newborn bloodspot screening, thyroid function tests (free thyroxine, fT4 and TSH) should only be ordered after consultation with the local paediatric/neonatal team.
  • Newborn bloodspot screening is the only test required to detect congenital hypothyroidism in well, term, singleton newborns regardless of the aetiology of maternal hypothyroid status.1,2
  • All infants with suspected neonatal thyrotoxicosis require urgent referral to an endocrinologist for advice on investigations and therapy.
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Please note that all guidance is currently under review and some may be out of date. We recommend that you also refer to more contemporaneous evidence in the interim.

Background

Thyroid hormones are essential for brain development. There are two active thyroid hormones:

  • T4 which is solely a product of the thyroid gland
  • T3 which is produced through the de-iodination of T4.

Eighty per cent of T3 is produced from conversion of thyroxine by organs such as the liver and kidneys. T3 is the more metabolically active hormone and is four times as potent as T4. Iodine is essential for normal thyroid function.3

During pregnancy, the fetus is dependent on maternal thyroxine (T4) crossing the placenta. The fetus de-iodinates the T4 to produce triiothyronine (T3), which is important for neurological development. Maternal T3 does not cross the placenta and appears to have little, if any, role in development.3

The normal term newborn has a rapid TSH surge within 30 minutes of birth that stimulates thyroidal T4 secretion, with peak fT4 and fT3 (free triiodothyronine) levels at 24-36 hours of life. Therefore, TFTs conducted immediately after birth can be difficult to interpret, while screening before 48 hours of age produces a high rate of false positive elevation in TSH.4 Newborn bloodspot screening is performed after 48hrs of age so as to avoid measuring the early rise in TSH.1

 fT3 measurements are generally not necessary in newborn infants

Preterm TFT results should be interpreted with caution, with endocrinology consultation recommended.4

Neonatal congenital hypothyroidism

Congenital hypothyroidism in neonates is characterised by decreased, or in rare cases, no thyroid hormone production. Early diagnosis is critical to prevent neurodevelopmental disability and to optimise developmental outcomes.

All newborns have screening for congenital hypothyroidism at 48-72 hours age with the newborn bloodspot screening test, which measures elevations in TSH, and does not measure fT4 levels. Infants at risk of a late TSH rise may have second and subsequent bloodspot tests requested by The Victorian Clinical Genetics Services (VCGS). Newborn bloodspot screening is the only test required to detect congenital hypothyroidism in well, term, singleton infants regardless of the aetiology of maternal hypothyroid status (including Hashimoto’s thyroiditis and subclinical hypothyroidism of pregnancy).1,2

The newborn bloodspot screening test will not detect low levels of TSH. Therefore, infants with clinical signs suggestive of central hypothyroidism (Table 1) or suspicion of hypothalamic-pituitary axis dysfunction (i.e. hypopituitarism) should have TFTs taken via a capillary or venous sample no earlier than day five of life.5

Table 1: Clinical features of neonatal hypothyroidism

Age
Clinical signs/features

Birth

Post term, large for dates, transient temperature instability, large posterior fontanelle, goitre

Early signs

Hypotonia, poor feeding, failure to thrive, prolonged jaundice

Late signs

Failure to thrive, constipation, lethargy, dry skin, hair, umbilical hernia, distended abdomen, macroglossia, hoarse cry, coarse facies, hypotonia, microcephaly, developmental delay


Infants with a positive bloodspot test require urgent collection of blood for TFTs to confirm the dignosisdiagnosis. Once hypothyroidism is confirmed, contact should be made with the on-call endocrinologist at either:

  • The Royal Children’s Hospital: 03 9345 5522
  • Monash Children’s Hospital: 03 9594 6666.

Treatment with thyroxine at 8-15micrograms/kg/day is usually commenced immediately upon confirmation of the diagnosis.6

Neonatal hyperthyroidism

Neonatal thyrotoxicosis is a rare condition that can be life threatening if untreated. It is caused by trans-placental transfer passage of TSH receptor antibodies (TRAb), usually in the presence of maternal Graves' thyrotoxicosis (and rarely from Hashimoto's thyroiditis) in the third trimester causing stimulation of the fetal thyroid gland.7

Neonatal hyperthyroidism will not be detected through newborn bloodspot screening and infants should be investigated as per the flow chart.

Infants at high risk of neonatal thyrotoxicosis include8:

  • those with a family history of TSH receptor mutation
  • those born to mothers with maternal Graves' disease and:
    • elevated TRAb in the third trimester (the higher the maternal TRAb concentration is during the third trimester, the greater is the likelihood of neonatal Graves' hyperthyroidism
    • thyrotoxicosis develops or requires treatment during pregnancy, particularly in the third trimester
    • treatment with carbimazole or propylthiouracil during the third trimester
    • antenatal evidence of fetal thyrotoxicosis (advanced bone age, craniosynostosis, hydrops associated with tachycardia/arrhythmia, fetal growth restriction, preterm, excessive movement, goitre).

Clinical features of neonatal hyperthyroidism usually present by 10 days of age. They may be apparent shortly after birth or may be delayed because of the effect of either the maternal anti-thyroid medications or the co-existent blocking antibodies. As the half-life of TRAb is only a few weeks, the natural history of neonatal hyperthyroidism is complete resolution by three to 12 weeks' of age.

Table 2: Signs of neonatal thyrotoxicosis

Clinical Signs
Physiological effects of thyroid hormones

Irritability, jitteriness, restlessness

TH stimulation of CNS (including disruption of sleep wake cycle), muscular tissue

Exopthalmos

Oedema and fat deposition

Tachycardia, arrhythmias, cardiac failure

Excessive myocardial stimulation from fT4, increased metabolic rate

Increased appetite, vomiting, diarrhoea, excessive weight loss, failure to regain birthweight

Gastrointestinal hyperactivity from fT4 stimulation

Craniosynostosis / frontal bossing / microcephaly

Advanced skeletal maturation

Temperature instability, sweating

Increased metabolic rate

Hepatosplenomegaly, thrombocytopaenia, lymphadenopathy

Goitre

Thyroid gland hyperplasia


Infants at risk for developing neonatal hyperthyroidism require observation for at least four days in hospital.

Infants at risk of developing neonatal thyrotoxicosis must be referred to the neonatal/paediatric team after birth for assessment and to arrange appropriate TFTs and follow-up.

Infants with suspected neonatal thyrotoxicosis require urgent TFTs regardless of postnatal age and referral to an endocrinologist for advice on further investigations and therapy.

More information

Clinical

  1. McGovern M, Reyani Z, O’Connor P, White M, Miletin J. Thyroid function testing in neonates born to women with hypothyroidism. European journal of pediatrics. 2016 Dec 1;175(12):2015-8.
  2. Ogundele MO, Waterson M. When should we be conducting thyroid function tests in newborns and young infants? Archives of disease in childhood. 2010 Feb 1;95(2):151-2.
  3. Burrow GN, Fisher DA, Larsen PR. Maternal and fetal thyroid function. New England Journal of Medicine. 1994 Oct 20;331(16):1072-8.
  4. Ogilvy-Stuart AL. Neonatal thyroid disorders. Archives of Disease in Childhood-Fetal and Neonatal Edition. 2002 Nov 1;87(3):F165-71.
  5. Underland L, Kenigsberg L, Derrick KM, Crespi R, Kaushal T, Lam L. Thyroid function testing in neonates with maternal history of disease. Clinical pediatrics. 2018 Apr;57(4):436-41.
  6. Australasian Paediatric Endocrine Group. Guidelines for management of congenital hypothyroidism.
  7. Alexander EK, Pearce EN, Brent GA, Brown RS, Chen H, Dosiou C, Grobman WA, Laurberg P, Lazarus JH, Mandel SJ, Peeters RP. 2017 Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum. Thyroid. 2017 Mar 1;27(3):315-89.
  8. Samuels, SL, Namoc SM, Bauer AJ. Neonatal Thyrotoxicosis. Clinics in Perinatology. 2018 Mar 1;45(1):31-40.

Related

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Centre of Clinical Excellence - Women and Children
Safer Care Victoria

Version history

First published: August 2015

Last reviewed: October 2018

Review by: December 2020

UNCONTROLLED WHEN DOWNLOADED

Page last updated: 17 Feb 2021

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