Thyroid Screening for Babies of Mothers with Thyroid Disease

Take-home

Who needs extra screening?

Every baby in Victoria has a newborn bloodspot screen (the heel-prick test) at 48–72 hours. This checks for congenital hypothyroidism and about 30 other conditions. It is an important screen, but it is not designed to pick up antibody-driven thyroid problems that develop in the first days or weeks of life.

Your baby needs additional thyroid checks if you:

• Have active or previously treated Graves’ disease (even if your thyroid was removed or ablated)
• Have Hashimoto’s thyroiditis with high TSH-receptor-blocking antibodies
• Took antithyroid medications (carbimazole, methimazole, propylthiouracil) during pregnancy
• Had high TRAb levels on testing in pregnancy

Why it matters

Mother’s thyroid antibodies travel across the placenta and can act on the baby’s thyroid for weeks to months, even if mum has been well controlled. There are two patterns:

Graves’ antibodies (TSH-receptor stimulating)

• Can cause neonatal hyperthyroidism (overactive thyroid)
• Typically appears within the first 2 weeks of life, occasionally later
• Affects around 1–5% of babies of mothers with Graves’ disease

Hashimoto’s antibodies (TSH-receptor blocking)

• Can cause transient hypothyroidism (underactive thyroid)
• Much less common
• Usually settles as antibodies clear

Your baby’s testing schedule

Typical plan (individualised to your baby)

• At birth (cord blood): TSH, Free T4, and TRAb if mother has Graves’ disease
• Day 3–5: repeat TSH and Free T4
• Day 10–14: TSH and Free T4, this is the critical window when hyperthyroidism often appears
• 4–6 weeks: final check as maternal antibodies decline

The routine newborn bloodspot test at 48–72 hours stays in place in addition to these.

Testing frequency increases if any result is abnormal or symptoms appear.

Signs to watch for at home

Neonatal hyperthyroidism (overactive thyroid)

Usually appears in the first 2 weeks.

• Irritability, agitated feeds, trouble settling
• Poor weight gain despite feeding well
• Fast heart rate (over 160 beats per minute at rest)
• Sweating or flushing
• Prominent or “starey” eyes
• An enlarged neck (goitre)
• Loose stools

Neonatal hypothyroidism (underactive thyroid)

• Prolonged jaundice beyond 2 weeks
• Very sleepy or hard to wake
• Poor feeding
• Constipation
• Cool, mottled skin
• Large tongue or poor muscle tone
• Hoarse cry
• Umbilical hernia

Treatment

For hyperthyroidism

• Antithyroid medications (methimazole or propylthiouracil)
• Beta-blockers if the heart rate is high
• Close monitoring: daily vitals in hospital and weekly blood tests
• Duration: usually 2–3 months while maternal antibodies clear

For hypothyroidism

• Thyroxine (levothyroxine): a tiny once-a-day tablet crushed into a little breast or formula milk
• Dose based on weight and blood levels
• Monitoring: thyroid function tested every 2–4 weeks initially, then less often
• Duration: often only until antibodies clear (3–6 months); permanent treatment is rare in this antibody-driven form

Long-term outlook

Antibody-driven thyroid problems clear as the maternal antibodies leave the baby’s system, usually by 3–6 months. With proper monitoring and treatment:

• Growth and development stay on track
• Babies do not have a higher risk of thyroid disease later in life
• Treatment can usually be stopped completely once antibodies clear
• Follow-up is with a paediatric endocrinologist initially, then gradually spaced out

When to seek help

What about the standard newborn screen?

The Victorian newborn bloodspot screening at 48–72 hours is a separate test. It reliably detects congenital hypothyroidism (where a baby is born with a small, missing, or poorly developed thyroid) and other rare conditions, but it is not designed to detect antibody-driven thyroid disease that shows up later. That is why your baby needs both sets of tests.

Summary

Key points to remember

• Babies of mothers with Graves’ or Hashimoto’s need extra thyroid tests
• Problems are usually temporary and respond quickly to treatment
• Watch for signs in the first 2–4 weeks and ring your paediatrician if you see any
• With follow-up, babies grow and develop normally
• Keep all scheduled appointments even if your baby seems fine

More information for parents

• RCH Kids Health Info
• Victorian Clinical Genetics Services — Newborn Screening