Thyroid disease in pregnancy — structured SAQ (15 marks)

(a) Physiology and immediate management (4 marks)

One mark per point, maximum four. ^[1][2]

• Physiology: pregnancy raises thyroid hormone demand through three mechanisms — oestrogen-driven rise in thyroxine-binding globulin (TBG), placental type 3 deiodinase stripping T4 to inactive forms, and fetal uptake. Established hypothyroidism requires a dose rise to maintain euthyroidism.^[1][2]
• Mechanism quantified: Alexander NEJM 2004 showed levothyroxine requirement rose a mean of 47 percent in the first half of pregnancy, with onset at a median of 8 weeks and a plateau by week 16.^[2]
• Immediate management: increase the levothyroxine dose by approximately 30 percent on confirmation of pregnancy — practically, two extra tablets per week. A woman on 100 micrograms daily now takes nine tablets per week (approximately 130 micrograms daily).^[1][2]
• Investigation: recheck TSH at 6 weeks to confirm euthyroidism and titrate further.^[1]

(b) TSH targets and monitoring plan (3 marks)

One mark per point, maximum three. ^[1]

• First trimester target: TSH below 2.5 mIU per L.^[1]
• Second and third trimester target: TSH below 3.0 mIU per L.^[1]
• Monitoring: TSH every 4 to 6 weeks throughout pregnancy, with dose titration to maintain the target. Step the dose back to pre-pregnancy at delivery and recheck TSH at 6 weeks postpartum.^[1]

(c) Pharmacological management of Graves across pregnancy (5 marks)

One mark per drug-specific point, with trimester logic. Marks are lost for "give antithyroid drugs" without specifics. ^[1][3]

• First trimester: propylthiouracil (PTU). Carbimazole and methimazole carry a teratogenic signal — aplasia cutis, choanal atresia, oesophageal atresia, omphalocele — with an adjusted odds ratio of 21.8 for this cluster in the Andersen Danish cohort.^[3]
• PTU dose: typical 50 to 150 mg three times daily, titrated every 4 to 6 weeks to the lowest dose that keeps the mother mildly thyrotoxic (avoiding fetal hypothyroidism).^[1][5]
• Second and third trimester: switch to carbimazole. PTU carries a small but real risk of fulminant hepatotoxicity; carbimazole is preferred beyond the first trimester. Typical carbimazole 5 to 15 mg daily.^[1]
• Beta-blockade: propranolol 20 to 40 mg up to four times daily, short course, for symptomatic control while the thionamide takes effect.^[1][5]
• Fetal monitoring: measure TSH-receptor antibody at 18 to 22 weeks; serial fetal ultrasound for goitre, tachycardia (above 160 bpm), growth restriction and hydrops; alert neonatal team for transient neonatal hyperthyroidism.^[1][5]

(d) Postpartum thyroid considerations (3 marks)

One mark per point, maximum three. ^[1]

• Antithyroid drugs and breastfeeding: both carbimazole (up to 30 mg daily) and PTU (up to 450 mg daily) are compatible with breastfeeding; take the dose immediately after a feed.^[1]
• Graves flare: Graves frequently flares in the postpartum period; counsel on monitoring and on the possibility of relapse requiring restart of antithyroid drugs. Recheck TFTs at 6 weeks and 3 months postpartum.^[1][5]
• Avoid overtreatment: Korevaar Lancet DE 2016 showed an inverted-U between maternal free T4 and offspring IQ — both low and high FT4 reduce child IQ by 1.4 to 3.8 points. The aim is the lowest effective antithyroid drug dose, not biochemical normalisation.^[6]