A 26-year-old woman, gravida 1 para 0, at 16 weeks gestation comes to the clinic for follow-up prenatal care. She was diagnosed with Graves disease during her first trimester and was treated with propylthiouracil, which was changed to methimazole 3 weeks ago. The patient has gained 7 kg (15.4 lb) over the last 4 months. She also has experienced increasing fatigue and states, "My breasts feel very full." The patient has had no palpitations or shortness of breath, but her sleep has been interrupted by frequent urination. Her mother has hypothyroidism, which is treated with levothyroxine. The patient has never used tobacco, alcohol, or illicit drugs. Temperature is 37.2 C (99 F), blood pressure is 112/72 mm Hg, pulse is 90/min and regular, and respirations are 18/min. No murmurs are heard on cardiac auscultation. Thyroid examination shows mild, diffuse enlargement with no tenderness or bruit. Deep tendon reflexes are brisk but symmetrical. The remainder of the physical examination is normal. Thyroid function test results are as follows: Which of the following is the most appropriate management for this patient?

Question

A 26-year-old woman, gravida 1 para 0, at 16 weeks gestation comes to the clinic for follow-up prenatal care.  She was diagnosed with Graves disease during her first trimester and was treated with propylthiouracil, which was changed to methimazole 3 weeks ago.  The patient has gained 7 kg (15.4 lb) over the last 4 months.  She also has experienced increasing fatigue and states, "My breasts feel very full."  The patient has had no palpitations or shortness of breath, but her sleep has been interrupted by frequent urination.  Her mother has hypothyroidism, which is treated with levothyroxine.  The patient has never used tobacco, alcohol, or illicit drugs.  Temperature is 37.2 C (99 F), blood pressure is 112/72 mm Hg, pulse is 90/min and regular, and respirations are 18/min.  No murmurs are heard on cardiac auscultation.  Thyroid examination shows mild, diffuse enlargement with no tenderness or bruit.  Deep tendon reflexes are brisk but symmetrical.  The remainder of the physical examination is normal.  Thyroid function test results are as follows:  Which of the following is the most appropriate management for this patient?

Quizplus · Accepted Answer

Explanation: Management of hyperthyroidism during pregnancy can be challenging as physiologic changes in the thyroid axis can resemble mild thyrotoxicosis, with: Increased total T4 High-normal or mildly elevated free T4 Suppressed TSH The interpretation of thyroid hormone and TSH levels should be based on pregnancy-specific reference ranges (normal total T3 and T4 can be approximated by 1.5 x nonpregnant reference ranges). Mild thyrotoxicosis during pregnancy does not require treatment. However, moderate-to-severe thyrotoxicosis due to Graves disease or nodular thyroid disease should be treated with thionamide antithyroid drugs (eg, methimazole, propylthiouracil). Propylthiouracil is preferred in the first trimester due to the potential teratogenicity of methimazole (aplasia cutis), whereas methimazole is preferred in the second and third trimesters (and in nonpregnant patients) due to the risk of hepatotoxicity with propylthiouracil (Choice B). Overtreatment of hyperthyroidism during pregnancy can lead to fetal hypothyroidism and goiter, so treatment should be titrated to maintain a mild hyperthyroid state. This patient's test results are appropriate for hyperthyroidism in pregnancy, and her current therapy should be continued without any dose adjustments (Choices D and E). (Choice A) Beta blockers are used to control the hyperadrenergic symptoms of hyperthyroidism (eg, tachycardia, palpitations). Short-term (<6 weeks) use of metoprolol or propranolol (but not atenolol) is considered safe in pregnancy. However, this patient's symptoms (weight change, fatigue, breast fullness, frequent urination) can be attributed to normal pregnancy and she is not overtly tachycardic; therefore, beta blockers are not necessary. Educational objective: Hyperthyroidism in pregnancy is treated with antithyroid drugs. Overtreatment of maternal hyperthyroidism can cause fetal hypothyroidism and goiter, so treatment should be titrated to maintain a mild hyperthyroid state. Propylthiouracil is preferred in the first trimester (due to the teratogenic effects of methimazole), but methimazole is preferred in the second and third trimesters (due to the hepatotoxicity of propylthiouracil). References: 2017 guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum. (http://www.ncbi.nlm.nih.gov/pubmed/28056690)

A 26-Year-Old Woman, Gravida 1 Para 0, at 16 Weeks