Background: There have been several published reports that hypothyroid women do not need to increase the dose of levothyroxine when they become pregnant.
Methods: For this study, 20 pregnant women who were hypothyroid as a result of surgical thyroidectomy, radio-iodine therapy, or combination therapy were followed for the duration of their pregnancies. These patients were seen regularly, and evaluated clinically and by measurement of free thyroxine (FT4) and thyrotropin (thyroid-stimulating hormone [TSH]).
Results: The amount of levothyroxine that was adequate in the nonpregnant state was found to be inadequate during pregnancy. The dosage of levothyroxine given to these patients was increased by an average of 36 micrograms and returned to earlier levels after delivery. There was considerable individual variation in the requirement for additional levothyroxine during pregnancy.
Conclusions: For hypothyroid pregnant patients, thyroid function tests, especially TSH, are recommended during each trimester to determine the need for additional levothyroxine.