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Congenital hypothyroidism
Congenital hypothyroidism is almost silent at birth, so it is found by newborn screening; levothyroxine 10–15 mcg/kg per day started within the first two weeks prevents intellectual impairment.
Why it matters in the exam
The question usually describes an abnormal screening result and asks for the next step: send venous TSH and FT4 and start treatment at once, without waiting for imaging. Another question describes a two-month-old with prolonged jaundice, a large posterior fontanelle, macroglossia, an umbilical hernia, constipation, hypotonia and a hoarse cry — signs that appear only when the diagnosis was missed.
The commonest cause is thyroid dysgenesis — mainly an ectopic gland — followed by defects in hormone synthesis. Transient causes are maternal blocking antibodies, iodine exposure or deficiency, and antithyroid drugs taken by the mother. In preterm and sick infants the TSH rise can be delayed, so screening is repeated at 2–4 weeks of age.
Treatment targets: normal FT4 within two weeks and normal TSH within 4 weeks, with close follow-up in the first year. The tablet is crushed and given in a little liquid, not together with soy, iron or calcium. Central hypothyroidism (low FT4 without raised TSH) may be missed by TSH-only screening and is linked to other pituitary deficiencies. When no permanent cause is found, a trial off treatment is possible from age 3.
Key points
- Most newborns with congenital hypothyroidism look normal at birth.
- Abnormal screen → venous TSH and FT4 and treat at once.
- Levothyroxine 10–15 mcg/kg per day; normal FT4 within two weeks.
- The commonest cause: dysgenesis, mainly an ectopic gland.
- Preterm infants — repeat screen at 2–4 weeks.
Summary table
| Situation | Findings | Work-up | Treatment |
|---|---|---|---|
| Abnormal screen | High TSH on the heel-prick test | Venous TSH and FT4 | Levothyroxine at once, without waiting for imaging |
| Established disease that was missed | Prolonged jaundice, large posterior fontanelle, macroglossia, umbilical hernia, constipation, hoarse cry | High TSH, low FT4 | Levothyroxine 10–15 mcg/kg per day |
| Dysgenesis (including ectopy) | The most common cause | Ultrasound or scintigraphy — never delaying treatment | Lifelong treatment |
| Transient | Maternal blocking antibodies, iodine, maternal drugs | TRAb antibodies, maternal history | Treat and trial off treatment from age 3 |
| Central | Low FT4, normal or low TSH; micropenis, hypoglycaemia | Pituitary work-up (cortisol, GH) | Exclude cortisol deficiency first, then levothyroxine |
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Sources
- ESPE/ENDO-ERN Congenital Hypothyroidism: A 2020–2021 Consensus Guidelines Update, 2021 — Screening, diagnosis and levothyroxine treatment
- AAP Clinical Report: Congenital Hypothyroidism: Screening and Management, 2023 — Newborn screening follow-up and treatment targets
- Nelson Textbook of Pediatrics, 22nd edition (2024) — Hypothyroidism
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.