Thyroid Disease

Question 1

How does pregnancy affect thyroid function?

Answer 1

hCG (structurally similar to TSH) stimulates thyroid → physiological ↑free T4, ↓TSH in first trimester
↑TBG (thyroxine-binding globulin) → ↑total T4 (use free T4 for assessment)
Increased iodine requirements (excreted more by kidneys + fetal demands)
Thyroid gland may enlarge slightly (physiological)

Question 2

How is hypothyroidism managed in pregnancy?

Answer 2

Levothyroxine: Increase dose by 25-50mcg as soon as pregnancy confirmed
Some recommend increasing pre-pregnancy dose by 25-50%
Check TSH every 4-6 weeks in first half of pregnancy, then at least once per trimester
Target TSH in trimester-specific reference range (generally <2.5 mU/L first trimester, <3.0 second/third)
After delivery → return to pre-pregnancy dose; check TSH at 6-8 weeks

Question 3

What are the risks of untreated hypothyroidism?

Answer 3

Miscarriage
Pre-eclampsia
Placental abruption
FGR
Preterm delivery
Impaired neurodevelopment in child
Postpartum haemorrhage

Question 4

How do you manage subclinical hypothyroidism in pregnancy?

Answer 4

TSH elevated, free T4 normal
If TPO antibodies positive → treat with levothyroxine (higher risk of progression and adverse outcomes)
If TPO negative → may still treat (varies by guideline; discuss with endocrine)
Monitoring recommended

Question 5

How is hyperthyroidism managed in pregnancy?

Answer 5

Propylthiouracil (PTU): Preferred in first trimester (carbimazole associated with aplasia cutis, choanal/oesophageal atresia)
Carbimazole/methimazole: Can use in 2nd and 3rd trimesters (switch from PTU at ~16 weeks — PTU carries hepatotoxicity risk)
Use lowest effective dose — aim free T4 at upper end of normal range
Block-and-replace regimen is CONTRAINDICATED (thyroxine doesn’t cross placenta adequately; excess antithyroid drug causes fetal hypothyroidism)
Radioactive iodine ABSOLUTELY CONTRAINDICATED (destroys fetal thyroid)
Monitor for fetal/neonatal thyrotoxicosis — TSH receptor antibodies (TRAb) cross placenta. Check TRAb at booking and ~28-32 weeks. If elevated → fetal monitoring (tachycardia, growth, goitre)
Thyroid crisis/storm: IV fluids, propranolol, PTU, hydrocortisone, cooling — obstetric and endocrine emergency
Most cases of Graves’ improve in pregnancy (immune suppression) but may flare postpartum

Question 6

How is postpartum thyroiditis managed?

Answer 6

Occurs in 5-10% of women
Typically: thyrotoxic phase (2-6 months) → hypothyroid phase (3-12 months) → recovery
Thyrotoxic phase: symptomatic treatment with propranolol (NOT antithyroid drugs — this is destructive thyroiditis, not overproduction)
Hypothyroid phase: levothyroxine if symptomatic
20-30% develop permanent hypothyroidism → annual TSH monitoring
More common with TPO antibody positivity and T1DM