Fetal complication of thyrotoxicosis 

• Fetal tachycardia, 
• Intrauterine growth retardation, 
• Prematurity, stillbirth 
• Congenital malformations

Fetal complication of over treatment with ATD

• Hypothyroidism→ poor brain development 
• Goiter 

1. Drug treatment

Newly diagnosed hyperthyroidism during pregnancy (gestational thyrotoxicosis)

• B-adrenoceptor antagonists (B-blockers) in the short term 
• Antithyroid drugs:
  • Propylthiouracil (PTU) is the preferred antithyroid drug 
  • Carbimazole: during the first trimester →choanal atresia and aplasia cutis.

Hyperthyroid women who become pregnant 

• Continue current drug (carbimazole or PTU) in pregnancy, with close monitoring.

**To avoid fetal hypothyroidism, it is important to use the smallest dose of antithyroid drug (typically < 150 mg PTU or 15 mg carbimazole per day) that will maintain maternal free T4, T3 and TSH concentrations within their respective reference ranges.

1. Thyroid Surgery

• Poor drug adherence
• Drug hypersensitivity
• Failure of medical treatment / large dose 
• Safely performed during the Second trimester.
• Preparation: Beta blocker, short course of KI

1. Radioiodine therapy

• Absolutely contraindicated in pregnancy → invariably induce fetal hypothyroidism 

** Frequent review of mother and fetus (monitoring heart rate and growth) is important during pregnancy and in the puerperium.

** Serum TRAb levels can be measured in the Third trimester to predict the likelihood of neonatal thyrotoxicosis.

ATD during lactation

• PTU is the drug of choice in the breastfeeding mother, as it is excreted in the milk to a much lesser extent than carbimazole. 
• Should be administered following a feeding and in divided doses
• Thyroid function should be monitored periodically in the breastfed child.

SAQ. A 24 year old woman with 8 weeks of pregnancy presented with palpitation, weight loss, and sweating. Lab reports showed TSH <0.01 mIU/L, FT4-42 nmol/L.

1. Mention 2 differentials for this condition?

• Gestational transient thyrotoxicosis
• Graves’ disease

1. What immediate investigation would you suggest?

• TSH receptor antibody (TRab)

1. What is your management plan for this lady?

During pregnancy

• First trimester: B blocker, propylthiouracil <150 ug/day, (carbimazole 15 mg/day if ongoing)
• 2nd trimester: Continue the current medications, thyroid surgery if needed 
• 3rd trimester: Monitoring TRab, if not elevated discontinue before 4 weeks of EDD.

During Delivery

• In hospital in presence of an endocrinologist and obstetrician.
• Mode of delivery as per obstetrician suggests.

Breast feeding: 

• Propylthiouracil, 
• Monitoring of LFT.