Dr Rachel Tattersall, Dr Yadlapalli Kumar
Untreated thyroid disease in a baby can have life long consequences – but the good news is that with the right treatment, these babies can have normal outcomes.
Thyroid problems in the newborn baby include congenital hypothyroidism and neonatal thyrotoxicosis.
The signs and symptoms of thyroid problems can be very subtle after birth – so it’s important that we have a good screening system. This makes sure that no babies with thyroid disease are missed, and identifies them as early as possible so that they can quickly start treatment.
In the past (before screening programmes were a thing) thyroid problems could be missed for weeks or months – this late diagnosis meant that babies missed out on early treatment, and some went on to have learning difficulties.
With early diagnosis and treatment, normal neurodevelopmental outcomes can be expected.
Screening is carried out via two pathways – the day 5 blood spot or ‘Guthrie test’, and clinical assessment guided by maternal risk factors.
Primary congenital hypothyroidism
This affects about one in every 2000-3000 babies born in the UK.
Primary Congenital hypothyroidism (CHT) can be due to:
- Thyroid dysgenesis – no thyroid gland, underdeveloped or ectopic thyroid gland;
- Dyshormonogenesis – thyroid gland is there but not working properly;
- Rarer causes in the UK include iodine deficiency, TSH resistance and maternal thyroid antibodies
Symptoms of hypothyroidism can include increased sleepiness, reduced or slow feeding, constipation, prolonged jaundice, cold extremities, poor tone and poor growth. Thyroid function tests (TFTs) are sometimes included as part of a prolonged jaundice screen, especially if the baby has not regained their birth weight.
Thyrotoxicosis is a potential risk in any baby born to a mother who has had thyroid disease – either hypo or hyperthyroidism – so we should make sure to take a detailed history of mum’s thyroid issues and how they have been treated and managed.
A baby born to a mother who has positive TSH-receptor antibodies, or who had clinical thyrotoxicosis in the third trimester, is at high risk for neonatal thyrotoxicosis.
A baby born to a mother who has had previous treatment for hyperthyroidism has a lower risk for thyrotoxicosis – see the flow chart below.
A baby can show signs and symptoms of thyrotoxicosis at birth, but symptoms might only begin after a few days of life – affected babies will usually be symptomatic by 10 days of age.
Clinical signs include goitre, tachycardia, periorbital oedema, weight loss, diarrhoea, sweating, hepatosplenomegaly, bruising and petechiae. Thyrotoxicosis can be fatal – careful treatment and management is needed, in close discussion with a paediatric endocrinologist. Carbimazole to treat thyrotoxicosis is often only needed for a very short period (i.e. less than one week) as the thyrotoxicosis is because of maternal antibodies, which transfer across the placenta, stimulating the fetal thyroid, and once these disappear, the symptoms of thyrotoxicosis should resolve.
Maternal risk factors
This is how we use the mum’s medical history of thyroid disease to help decide what level of thyroid screening is needed:
If a mother has only ever been on thyroxine then the risk of neonatal thyroid problems are low and routine bloodspot testing is all that’s needed.
However, if the mum has ever had thyroid surgery, radionucleotide treatment and/or previous or current treatment with Carbimazole or Propylthiouracil then the baby is at a higher risk of having a thyroid problem and needs to be reviewed by a paediatric doctor after birth.
Carbimazole and propylthiouracil can cross the placenta, so they have a risk of causing fetal hypothyroidism and goitre. The higher the maternal TSH-receptor antibody titre, the higher the risk of neonatal thyrotoxicosis.
This flow chart can help with risk stratification:
Screening for thyroid disorders
Congenital hypothyroidism is usually picked up by the day 5 bloodspot – if a raised TSH is detected up on the Guthrie test, the screening lab will refer this baby for an urgent clinical review.
Thyrotoxicosis, on the other hand, is investigated and examined for based on risk assessments (as per flow chart).
Newborn bloodspot results:
Newborn babies who have a bloodspot TSH concentration of >20mU/l WB () are referred as “CHT suspected”. Those with a result <8mU/l WB are classed as “CHT not suspected” and no further referral or testing is done.
Those that are in the ‘borderline’ category – with a bloodspot TSH between 8-20mU/l WB – need to have a repeat sample 7-10 days later. If the result is still borderline or it rises above 20mU/l they will also be referred by the screening laboratory as “CHT suspected”.
For babies born under 32 weeks gestation, the bloodspot test is checked twice, and referral is only made if the second result is abnormal. For example, they are referred as “CHT not suspected” if TSH <8mU/l WB on the second sample, and are referred as “CHT suspected” if the TSH is >20mU/l WB. For the borderline results, they are referred if the third sample is 8-20mU/l WB.
What happens after a referral
Any “CHT suspected” result needs an urgent referral to the paediatric team – the baby should ideally be seen that same day, by a paediatrician with endocrinology expertise.
The paediatrician will take a history and do a thorough clinical exam. Babies with CHT can have other associated congenital problems such as hearing loss and cardiac defects. They will be examined carefully for hypotonia, prolonged jaundice, umbilical hernia, dry skin and any dysmorphic features.
Clinical signs and symptoms of neonatal HYPOthyroidism
The baby then needs blood tests – checking TSH and free T4 is essential but other tests such as free T3, thyroid peroxidase antibodies, thyroglobulin (indicator of thyroid tissue presence), bone profile, U+Es and FBC may be done.
It is important to note that venous TSH results are double WB.
In an ideal world, thyroid imaging should happen on the same day and if possible should include a radioisotope scan, with or without a thyroid ultrasound. If for whatever reason the imaging can’t happen straight away, treatment should not be delayed. The radioisotope scan can be done within 5 days of starting treatment, and a thyroid ultrasound can be done at any time.
The imaging is important to help determine the type of CHT (by confirming whether the thyroid is present, absent, ectopic or underdeveloped).
The mum also needs blood tests – TSH and T4 at a minimum, and often thyroid peroxidase antibodies.
The parents should be given written information (as well as the verbal explanation you give!) about the diagnosis – your local trust may have their own information leaflet or there are information leaflets available from Public Health England, Child Growth Foundation or the British Thyroid Foundation have produced.
Who else needs to know? The baby’s GP and health visitor – and the newborn screening lab that picked up the initial result from the Guthrie test. Not only is this important to confirm that the baby has been promptly managed, but the information also feeds into national and regional audits.
ALL babies with a TSH concentration >20mU/l WB or >40 mu/l on serum TFTs should start levothyroxine by 14 days of age, whereas if the TSH was borderline the levothyroxine should be started by 21 days of age. The guidance states that the accepted treatment level is 100% – no patients can be missed.
The starting dose of oral levothyroxine should be 10 to 15 mcg/kg/day, with a maximum dose of 50 mcg/day.
Any patient with a TSH of >20mU/l WB (equivalent to venous TSH >40mU/l) should be started on treatment immediately – don’t wait for the venous results. For patients with a venous TSH of <40mU/l the flow chart here may be helpful in deciding on treatment:
The UK screening programme only tests for primary CHT, it does not test for secondary CHT such as with hypopituitarism. This is because only the TSH level is tested initially, not the free T4 level. In the Netherlands they do things a bit differently: free T4 is checked initially, and then TSH and thyroxine-binding globulin level. This approach screens for both primary and secondary CHT.
Patient information resources:
Child Growth Foundation Congenital Hypothyroidism leaflet
British Thyroid Foundation Congenital Hypothyroidism leaflet
Public Health England resources
Authors: Dr Rachel Tattersall (paediatric ST2), Dr Yadlapalli Kumar (Consultant paediatrician), Royal Cornwall Hospital