NEONATAL CONDITIONS
Neonatal Thyroid Abnormalities
A practical guide for SCN clinical staff · Congenital hypothyroidism and neonatal thyroid dysfunction - a preventable cause of intellectual disability
PROTECT
THE BRAIN
Fetal thyroid axis
Thyroid hormone is essential for brain development. The fetus relies on maternal T4 across the placenta early on, while the fetal gland and hypothalamic-pituitary-thyroid axis mature through the second and third trimesters.
Making the hormone
The thyroid traps iodide and uses thyroid peroxidase to build T4 (and some T3); pituitary TSH drives the gland, under negative feedback from circulating thyroid hormone.
Congenital hypothyroidism
Most cases are thyroid dysgenesis - an absent, hypoplastic or ectopic gland. A minority are dyshormonogenesis (an enzyme defect such as TPO), which is often inherited and can cause a goitre.
Primary vs central
Primary CH gives a low T4 with a high TSH - the basis of screening. Central (hypothalamic-pituitary) CH gives a low T4 with a low or normal TSH, so TSH-based screening misses it.
Why screening works
A raised heel-prick TSH flags primary CH before any symptoms, because maternal T4 masks the deficiency in the first days of life.
Untreated course
As maternal hormone clears, features appear - prolonged jaundice, poor feeding, constipation, hypotonia, a large fontanelle - and untreated CH causes irreversible intellectual disability.
Transient & maternal causes
Maternal Graves TRAb crosses the placenta and can cause transient neonatal thyrotoxicosis; blocking antibodies or antithyroid drugs cause transient hypothyroidism. Preterm or sick infants may have transiently abnormal TFTs.
CLINICAL FINDINGS (OFTEN SUBTLE)
- Often normal at birth because of maternal T4
- Prolonged jaundice, poor feeding, lethargy, hypotonia
- Constipation, large posterior fontanelle, macroglossia, umbilical hernia
- Hypothermia, dry skin, hoarse cry
- Thyrotoxicosis: tachycardia, irritability, poor weight gain, goitre
INVESTIGATIONS
- Newborn screening TSH (the key safety net)
- Confirmatory venous TFTs: free T4 and TSH
- Thyroid ultrasound or radionuclide scan (dysgenesis vs in-situ) - do not delay treatment for it
- Maternal thyroid history and TRAb if thyrotoxicosis is suspected
- Knee X-ray (absent distal femoral epiphysis) suggests severe, long-standing CH
COMPLICATIONS & RED FLAGS
- Delayed treatment of CH causes irreversible intellectual disability
- A normal screen does not exclude central (pituitary) hypothyroidism - check if suspicious
- Neonatal thyrotoxicosis can cause heart failure, arrhythmia and craniosynostosis - urgent
- In preterm or sick infants, interpret TFTs with caution and repeat
- Do not ignore prolonged jaundice - check TFTs
MANAGEMENT
Catch it on newborn screening, start levothyroxine promptly without waiting for imaging, and involve paediatric endocrinology.
Congenital hypothyroidism
- Start levothyroxine promptly (within the first 2 weeks) - do not wait for imaging
- Typical start 10-15 µg/kg/day, tablet crushed in a little milk or water
- Recheck TFTs to confirm and titrate; normalise free T4 quickly, then TSH
- Refer to paediatric endocrinology for follow-up
Neonatal thyrotoxicosis
- Antithyroid drugs (carbimazole/PTU) +/- a beta-blocker for symptoms
- Monitor for heart failure; supportive care
- Usually transient as maternal antibodies clear over weeks to months
- Involve endocrinology and cardiology
Follow-up
- Check hearing and review for other anomalies
- If dysgenesis is not proven, re-evaluate at ~3 years with a trial off therapy
- Educate parents on adherence and consistent dosing
- Arrange developmental surveillance
- Ensure newborn screening is done on time (day 2-3) and not missed - it is the safety net for congenital hypothyroidism.
- Flag prolonged jaundice, poor feeding, constipation or hypotonia for thyroid testing.
- For levothyroxine: give it consistently, crushed in a small amount of milk or water (not a full feed), and teach parents about adherence.
- In suspected thyrotoxicosis, monitor heart rate, feeding and weight and escalate signs of heart failure.
Why does newborn screening use TSH, and what does it miss?
Why must levothyroxine start before confirmatory imaging in congenital hypothyroidism?
How does maternal thyroid disease affect the baby, in both directions?
What are the long-term consequences of delayed treatment?
Take-home message: Congenital hypothyroidism is one of the few preventable causes of intellectual disability, caught by newborn screening (TSH) before symptoms appear. Start levothyroxine promptly - within the first two weeks and before imaging - and refer to endocrinology. Remember that central hypothyroidism can be missed by screening, and maternal Graves disease can cause transient neonatal thyrotoxicosis.
For educational purposes only. Always align management to current ANZCOR/NRP guidelines and your local SCN/NICU or NETS protocols.