Management of Thyrotoxicosis in Pregnancy

Primary Rationale: Elevated TRAb Levels

The American Academy of Family Physicians recommends that patients with elevated thyrotropin receptor antibodies (TRAb) levels, such as 200 IU/L, require continued treatment with methimazole throughout pregnancy to prevent fetal and neonatal thyrotoxicosis, regardless of current euthyroid status 1, 2
Maternal TRAb antibodies can cross the placenta and stimulate the fetal thyroid, leading to fetal thyrotoxicosis, which necessitates close monitoring and continued maternal treatment with methimazole 1, 2
The American Academy of Family Physicians suggests that the newborn's physician should be informed about maternal Graves' disease due to the risk of neonatal immune-mediated hyperthyroidism or hypothyroidism from transplacental antibody passage 3

Fetal thyrotoxicosis must be considered in women with a history of Graves' disease and elevated TRAb; the American Academy of Family Physicians recommends appropriate consultation should be sought if diagnosed 1, 2
The American Academy of Family Physicians notes that suppression of fetal thyroid function with methimazole therapy is usually transient and rarely requires treatment, making the benefits of maternal treatment outweigh this risk 3

The American Academy of Family Physicians recommends that proptosis alone is not a determining factor for treatment decisions in pregnancy, but rather TRAb levels and thyroid function 1, 2

The patient's symptoms of fatigue and palpitations, along with heart rate of 92-110 beats per minute on telemetry, suggest persistent hyperthyroidism requiring medication 4, 5

The goal of treatment is to maintain free T4 in the high-normal range using the lowest possible methimazole dosage to control symptoms while minimizing fetal exposure 4, 6
Monitor free T4 or FTI every 2-4 weeks to adjust dosage appropriately 6, 7
Beta-blockers (e.g., propranolol) can be used temporarily to control symptoms like palpitations until methimazole reduces thyroid hormone levels 6, 7

Regular monitoring of free T4 levels every 2-4 weeks initially, then every trimester 6, 7
Monitor fetal heart rate and growth; the newborn's physician should be informed about maternal Graves' disease due to risk of neonatal thyroid dysfunction 6, 5
Watch for side effects of methimazole including agranulocytosis (sore throat, fever), hepatitis, vasculitis, and thrombocytopenia 6

Suppression of fetal thyroid function with methimazole therapy is usually transient and rarely requires treatment 6