5th April 2024

Hyperthyroidism in pregnancy

To confirm biochemical hyperthyroidism during pregnancy, the following levels should be checked:

• Serum TSH
• Free thyroxine (FT4)
• Free triiodothyronine (FT3)

Serum TSH-receptor antibodies should be checked immediately once pregnancy is confirmed if there is current or previous history of Grave’s disease.

Risks associated with untreated hyperthyroidism in pregnancy include:

• Miscarriage
• Premature birth
• Low birthweight
• Preeclampsia
• Thyroid storm
• Congestive heart failure

Management can be difficult requiring specialist input. Propylthiouracil is preferred in early pregnancy as it is less likely to cross the placenta than carbimazole, which is associated with congenital abnormalities. Carbimazole is preferred later on in pregnancy due to the risk of severe hepatotoxicity associated with propylthiouracil. Radioactive iodine and traditional block and replace regimens are contraindicated in pregnancy. It is important to check TSH receptor antibody status at 24-28 weeks to assess the risk of foetal/neonatal hyperthyroidism.