From the Guidelines
The most appropriate management for this pregnant lady at 28 weeks gestation with symptomatic hyperthyroidism on 15mg carbimazole is to increase her carbimazole dose to 20-30mg daily while closely monitoring thyroid function. Given her low TSH and elevated T3 and T4 levels despite current therapy, the dose increase is necessary to achieve euthyroidism and prevent potential complications such as severe preeclampsia, preterm delivery, and heart failure 1. Thyroid function tests should be repeated every 2-4 weeks, aiming for free T4 levels in the upper normal range or slightly elevated, while avoiding hypothyroidism which could affect fetal development.
- Propylthiouracil (PTU) would typically be preferred in the first trimester due to lower risk of congenital anomalies, but switching at 28 weeks is unnecessary as the risk period has passed 1.
- The patient should be monitored for potential side effects of carbimazole including rash, agranulocytosis, and liver dysfunction.
- Fetal growth and well-being should be assessed regularly with ultrasound scans.
- Beta-blockers like propranolol can be considered for short-term symptomatic relief of palpitations and tremor. The goal is to use the lowest effective dose of antithyroid medication to control maternal symptoms while minimizing the risk of fetal hypothyroidism, as these medications cross the placenta and can affect fetal thyroid function 1.
From the Research
Management of Hyperthyroidism in Pregnancy
The management of hyperthyroidism in a pregnant lady at 28 weeks gestation, currently on 15mg carbimazole, presenting with symptoms of hyperthyroidism, low TSH, and elevated T3 and T4 levels, requires careful consideration of the potential risks and benefits of different treatment options.
Treatment Options
- Increase carbimazole dose: Increasing the dose of carbimazole to 20mg may be considered to achieve euthyroidism, as seen in a case report where a patient's dose was increased to 20mg thrice daily 2.
- Switch to Propylthiouracil (PTU): Switching to PTU may be considered, especially in the third trimester, as it is preferred in this trimester due to the potential risks of carbimazole 3.
- Referral for thyroidectomy: Referral for thyroidectomy may be considered in cases where medical management is not effective or feasible, as seen in a case report where a patient underwent thyroidectomy due to carbimazole resistance 2.
Considerations for Treatment
- Fetal thyroid status: The treatment should aim to maintain fetal thyroid status within normal limits, as fetal hypothyroidism can occur with both PTU and methimazole (MMI) 4.
- Maternal and fetal risks: The treatment should balance the risks of uncontrolled hyperthyroidism with the potential risks of antithyroid drugs, such as hepatotoxicity with PTU and choanal and esophageal atresia with MMI 3.
- Monitoring and adjustment: Regular monitoring of maternal and fetal thyroid function and adjustment of treatment as needed is crucial to prevent adverse effects on the mother, fetus, and neonate 5, 3.