Medscape Ob/Gyn > Ask the Experts > Obstetrics and Maternal-Fetal Medicine
Thyrotoxicosis in Pregnancy
Peter S. Bernstein, MD, MPH, FACOG, Karen L. Koscica, DO
Disclosures
April 15, 2003
PrintQuestion
A 28-year-old woman 7 weeks pregnant was referred to me by a GP in March. She was diagnosed with thyrotoxicosis in December 2002 and was given radioactive iodine in January 2003 -- before she became pregnant. This is her first pregnancy and she is very concerned. Termination of pregnancy is not an option. What else can be done? She is also taking propranolol.
Adanlawo Moses, FCOG
Response From the Expert
Karen L. Koscica, DO
Department of Obstetrics & Gynecology and Women's Health, Albert Einstein College of Medicine/Montefiore Medical Center, Bronx, New York
Peter Bernstein, MD, MPH
Associate Professor of Clinical Obstetrics & Gynecology and Women's Health, Albert Einstein College of Medicine/Montefiore Medical Center, and Medical Director, Obstetrics and Gynecology, Comprehensive Family Care Center of Montefiore Medical Group, Bronx, New York
Hyperthyroidism complicates about 0.2% of pregnancies. It is the second most common endocrine disorder seen in pregnancy -- second to diabetes. The most common cause is Graves' disease, which accounts for about 85% of the cases. It is an important entity to consider during pregnancy because of the increased risk to mother and fetus.[1]
The clinical manifestations of thyrotoxicosis in pregnancy can be confusingbecause pregnancy has similar manifestations, such as palpitations and heat intolerance. Common symptoms of thyrotoxicosis are fatigue, tiredness, palpitations, heat intolerance, insomnia, proximal muscle weakness, and shortness of breath. The most suggestive symptoms are failure to gain weight despite adequate intake and tachycardia.[1] Graves' ophthalmopathy occurs in about one third of patients.[2] Diagnosis is confirmed by laboratory testing of a decreased TSH and an elevated free T4.[1]
The mainstays of thyrotoxicosis treatment are the antithyroid drugs. The thionamides are the drugs used in treatment during pregnancy. The 2 main medications are propylthiouracil (PTU) and methimazole. Their function is to block thyroid hormone biosynthesis. Doses of 80-100 mg daily of methimazole or 800-1200 mg daily of PTU in divided doses 3 times daily are sufficient for control of hyperthyroidism. Once serum thyroid hormone levels return to normal it is necessary to decrease the dosing to 5-20 mg daily of methimazole or 50-300 mg daily for PTU for control.
Adverse reactions can occur with these medications. About 10% of patients will experience a skin rash. The rarest complication is agranulocytosis, which occurs in about 1 in 200, but it resolves once the medication is discontinued. A baseline white blood cell count is recommended.[2] Both medications cross the placenta to the fetus, but PTU crosses less readily than methimazole. If administered in high doses over a long term, PTU can cause fetal hypothyroidism, which is not common with the usually prescribed doses of < 300 mg daily of PTU and 20 mg daily of methimazole. Aplasia cutis has been described in about 20 infants exposed in utero to methimazole. The risk of occurrence when using this medication is unknown, but no adverse reactions to the fetus have been described with the use of PTU. Thus, PTU is typically preferred to methimazole.[2]
Other drugs to consider during pregnancy are beta-adrenergic blockers. These drugs have an adjunctive role in thyrotoxicosis. They help with the sympathetic manifestations. Propranolol modulates thyroid hormone blood levels through a mild inhibitory effect. The usual contraindications to beta-blockers are obstructive lung disease, heart block, heart failure, and insulin-dependent diabetes. Use of beta-blockers during pregnancy, however, has been associated with small risks of fetal growth restriction, neonatal bradycardia, and hypoglycemia, and even early pregnancy loss.[1,2] Nevertheless, the benefits of these agents in controlling a patient's thyrotoxicosis symptoms may outweigh the risks, particularly if they are necessary only for a short period of time to control the patient's thyroid
conditionhttp://www.medscape.com/viewarticle/451718C is correct
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