CASE 3: CARDIOVASCULAR SYMPTOMS
A 24-year-old primigravida woman presents with complaints of palpitations and increased anxiety. She is currently 28 weeks pregnant. Her TSH level is undetectable (< 0.01 mIU/L), and her free T4 is 2.1 mg/dL (reference range, 0.5-1.6 mg/dL). An ECG performed at your office shows sinus tachycardia with a rate of 127 beats/min.
Recommendation
Maternal hyperthyroidism increases risk for maternal congestive heart failure, uncontrolled hypertension, atrial fibrillation, and thyroid storm. Additionally, fetal hyperthyroidism can occur, especially if the mother has Graves disease. Since thyroid-stimulating immunoglobulins (TSI) can permeate the placental barrier, poor fetal growth, cardiac failure, and fetal thyrotoxicosis are severe adverse effects of in-utero TSI exposure.
To prevent further complications, antithyroid medications should be started in this case. Methimazole (MMI) carries a risk for a rare birth defect, aplasia cutis, in the first trimester and is best avoided during this time. Propylthiouracil (PTU) should be given in the first trimester and then switched to MMI in the second trimester to decrease the risk for hepatotoxicity associated with PTU. Breastfeeding mothers should be assured that low-dose MMI is generally considered safe for breastfed infants but should be taken after feeding in divided doses if possible.1
For symptom relief, b-blockers can be used, although they do come with some risks. As pregnancy Category C drugs, b-blockers are associated with neonatal growth retardation, hypoglycemia, hypoxia, lower Apgar scores, and neonatal respiratory distress.6 Consider giving the lowest dose possible for the duration of the patient’s symptoms.
Radioactive iodine (I-131) should not be given to patients who plan to become pregnant or who are pregnant.2,3 The Endocrine Society recommends that if a woman inadvertently becomes pregnant, she should be counseled on the risks of radiation to the fetus, which include thyroid destruction if treatment occurs/continues after the 12th week of pregnancy.2 Furthermore, pregnancy should be avoided for the first six months after thyroid ablation to allow sufficient time to obtain the target maternal serum TSH level of 0.3 to 2.5 mIU/L.
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