Thyroid hormone — especially T3 — acts directly on epiphyseal cartilage in long bones and amplifies GH and IGF-1 signaling. Each 6 months of untreated hypothyroidism can mean 1-3 cm of permanent height loss. Pediatric screening is therefore critical.
Screening: congenital hypothyroidism
Turkey runs newborn heel-prick screening since 1995:
- Sample at 48-72 hr
- TSH and T4
- TSH >20 mIU/L: strong positive → urgent referral
- TSH 10-20: equivocal → retest
- TSH <10: normal
Prevalence in Turkey: 1/1,500 — high, due to regional iodine deficiency. Ministry of Health + UNICEF programs initiate treatment within 7-14 days of positive screen.
Congenital hypothyroidism — causes
Primary (gland)
- Thyroid agenesis/dysgenesis (most common, 85%)
- Dyshormonogenesis (synthesis defect) — TPO deficiency, Pendred syndrome
- Maternal anti-thyroid antibody transfer — transient
Central (pituitary)
- TSH deficiency — panhypopituitarism
- Septo-optic dysplasia
- Birth trauma, intraventricular hemorrhage
Iodine deficiency in endemic areas
- Some Anatolian regions still marginally deficient
- Salt iodization has reduced this dramatically
Congenital hypothyroidism symptoms
Untreated:
- Prolonged jaundice (>3 weeks)
- Constipation
- Hypotonia
- Pale + cool skin
- Macroglossia
- Wide anterior fontanelle
- Feeding difficulty
- Mental retardation (irreversible if treatment delayed past 6 months)
This is why newborn screening is critical — start treatment before symptoms.
Treatment
- Levothyroxine (synthetic T4), 10-15 μg/kg/day
- Target: normal TSH, rapid T4 rise
- Retest at 4-6 weeks, titrate dose
- Lifelong treatment (congenital agenesis)
- Reassess at age 3 to distinguish agenesis vs transient
Early treatment (within first month) → normal IQ; late treatment → IQ -5 to -10.
Acquired hypothyroidism — children
Hashimoto's thyroiditis (most common)
- Autoimmune, anti-TPO + anti-Tg antibodies
- Onset usually 6-12 yrs
- Mild goiter
- Family history of thyroid + type 1 diabetes common
- Treatment: levothyroxine
Symptoms — school-age
- Slowing height growth (<4 cm/year)
- Percentile drop (channel crossing)
- Delayed puberty
- Weight gain (fat increase)
- Fatigue, cold intolerance, constipation
- Dry skin + hair
- Concentration difficulty, school performance drop
- Bradycardia
Important: these children may look like academic-problem cases, but thyroid might be the cause. Short stature + weight gain + dropping grades → TSH test.
Hyperthyroidism — rarer
Graves' disease
- Autoimmune, TSH-receptor antibody (TRAb)
- More common in adolescent girls
- Symptoms: weight loss, palpitations, tremor, heat intolerance, irritability, performance drop, exophthalmos
Impact on growth
- Short-term: rapid height gain, advanced bone age
- Long-term untreated: early epiphyseal closure → adult height loss
Treatment
- Antithyroid drug (methimazole) — first line
- Radioactive iodine — for adolescents 10+ yrs
- Thyroidectomy — refractory cases
Diagnostic algorithm
A pediatrician sees a child dropping below p3:
- History: family history, fatigue, constipation, cold intolerance
- Physical: height, weight, Tanner stage, thyroid palpation, reflexes
- Lab: TSH, free T4, anti-TPO
- Imaging (if needed): thyroid US (Hashimoto's heterogenous pattern)
- Bone age: BA behind CA → constitutional or thyroid?
Growth follow-up during treatment
After 6-12 months of treatment, expect catch-up growth:
- First-year height gain 8-12 cm (catch-up)
- Percentile uptrend
- Bone age catches up
- Menses normalize (girls)
Don't stop before catch-up completes — height loss can be permanent.
Sport and thyroid disorders
- Full activity after treatment stabilizes
- Monitor electrolytes + cardiac rhythm at therapy start
- Target TSH 0.5-2.0 for professional athletes
FAQ
When should thyroid screening be repeated?
Congenital screening done; routine repeat not needed unless symptomatic. But:
- Type 1 diabetes annually (autoimmune comorbidity ~20%)
- Down syndrome, Turner, celiac diagnosis annually
- Strong family history at adolescent onset
Is levothyroxine lifelong?
For congenital agenesis: yes. For Hashimoto's: usually yes (permanent gland damage). For transient hypothyroidism (re-evaluated at age 3), sometimes can be stopped.
Is iodized salt safe for children?
Yes — and necessary. Iodine-fortified salt reduced thyroid disorders by 40% in Turkey. Just avoid excess (1 tsp/day adult dose).
Is fertility possible with thyroid disorders?
Yes — with stable treatment. Hypothyroid women have 30% lower fertility but this normalizes post-treatment.
Bottom line
Thyroid health is the silent architect of child growth. Turkey's newborn screening program is gold standard; acquired cases need pediatric vigilance. For systematic growth + weight + percentile tracking, sign up free, bring PDF reports to your pediatrician.