Hyperthyroidism in Pregnancy

Question 1

Pathogenesis

Answer 1

• Grave’s Disease 95%
  o Autoimmune (TSH-receptor antibodies)
• Multinodular goitre
• Thyroiditis (subacute, viral)
• Medications – iodine, amiodarone, lithium

Question 2

Effect of Pregnancy on Hyperthyroidism

Answer 2

• tends to improve
• Can be worse in first trimester and postpartum

Question 3

Effect of Hyperthyroidism on pregnancy

Answer 3

MATERNAL
- anovulation/ Infertility
- miscarriage
- IUGR
- Preterm labour
- SVT/AF
- Anaesthetric risk if retrosternal goitre in labour
FETAL
- Fetal/ Neonatal Thyrotoxicosis (Antibodies cross the placenta)

Question 4

Relevant History

Answer 4

o Heat intolerance
o Tachycardia/palpitations
o Emotional lability
o Vomiting
o Weight loss
o Tremor
o Medications

Question 5

Relevant Examination

Answer 5

o BMI
o Eyes – lid lag, exophthalmos
o Goitre
o Palmar erythema

Question 6

Relevant investigations

Answer 6

o TFTs – suppressed TSH, elevated T3/T4
o TSH receptor antibodies
o Anti-TPO/anti-thyroglobulin to exclude thyroiditis

Question 7

Management

Answer 7

• Antithyroid drugs
  o Carbimazole
• Side effects: neutropaenia, agranulocytosis
• Fetal risk: aplasia cutis (absent skin)
  o PTU (propylthiouracil)
• Side effects: neutropaenia, agranulocytosis, severe liver impairment
• Less placental transfer than Carbimazole

Pre- Pregnancy:
- Switch from Carbimazole to PTU
- Aim for euthyroid pre preg
(Assess disease status, optimise disease status, rationalise medication)

Antenatal
- Multidisciplinary care team including Endocrinology
- Routine screening, investigations, supplementation
- Monitor TFT each trimester aiming for upper limit of normal range (Not block and replace as meds cross placenta while Thyroxine does not- will lead to neonatal hypothyroidism)
- If newly diagnosed in pregnancy monitory 4 weekly until stable at upper normal limit
- Avoid selective beta blockers if possible due to risk of IUGR
- THyroidectomy rarely required in pregnancy
- Radioactive Iodine contraindicated in pregnancy
- US surveillance for Fetal thyrotoxicosis if:
IUGR
Fetal tachycardia
goitre
OR graves disease with high antibody titres

Nil other changes to antenatal care
Nil changes to intrapartum care including timing and mode of delivery in absence of other Obstetric complications

Postpartum:
FETAL:
- Take TFTs from cord blood
- Observe for neonatal thyrotoxicosis (presents day 1-7 of life)
* 15% mortality if untreated
* Weight loss, tachycardia, irritability, poor feeding
* Treat with antithyroid drugs