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Treatment with fixed thyroxine doses in pregnant women with subclinical hypothyroidism

Seoane Cruz, Inés; Penín Álvarez, Manuel; Luna Cano, Reyes; García-Mayor, Ricardo Víctor

Published in Endocrinol Nutr. 2012;59:284-7. - vol.59 núm 05

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Abstract

Background

Hypothyroidism is usually treated with thyroxine doses on patient weight. In some cases, however, fixed doses have proved to useful to normalize TSH levels, which is especially important during pregnancy.

Patients and methods

Sixty-eight women diagnosed with subclinical hypothyroidism, autoimmune or not, during pregnancy were given a fixed dose of thyroxine 50mcg/day. TSH measurements were performed to assess the need to change the dose, which was increased or decreased by 25mcg/day when necessary.

Results

With a dose of 50mcg/day of thyroxine, 42% of patients reached a TSH level less than 3μU/mL, 79.4% reached a TSH level less than 4.5μU/mL, and 20.6% had TSH levels higher than 4.5μU/mL.

Discussion

Our data suggest that a fixed dose of thyroxine 50mcg/day is inadequate in a significant proportion of pregnancy-diagnosed hypothyroidism regardless of whether the reference of TSH level used is 4.5 or 3μU/mL. Starting dose of 75mcg/day is probably more adequate, but studies are needed to evaluate the possibility of overtreatment with such dose.

Key words: Hypothyroidism. Pregnancy. Treatment.

Introduction

Introduction Primary hypothyroidism is characterized by elevated plasma TSH levels. Hypothyroidism is called subclinical when the FT4 level is normal, and overt when the FT4 level is decreased. During pregnancy, TSH levels higher than 4.5μU/mL have been related to impaired fetal neurological and psychomotor development and an increased risk of premature labor, pre-eclampsia, and abruptio placentae,¹^,² and thyroxine treatment is usually given to normalize TSH levels.³^,⁴ It has even been proposed that the optimum TSH level in pregnant women is less than 2.5μU/mL during the first trimester and less than 3μU/mL during the second and third trimesters.³^,⁵^,⁶ The most commonly used approach for starting thyroxine replacement therapy consists of calculating hormone dosage based on the weight of each patient (a mean of 1.6μg/(kgday) are needed).⁷ An alternative that has been shown to be of value for elderly or cardiovascular patients⁸ consists of starting treatment at a fixed dose of 25–50μg/day of thyroxine, with subsequent adjustment based on TSH levels. Starting treatment with a loading dose is an increasingly popular approach, particularly for the management of overt hypothyroidism in pregnant patients.⁹ This study was intended to verify whether treatment with fixed thyroxine doses of 50μg/day is effective during pregnancy. Patients and methods All patients diagnosed with subclinical hypothyroidism during pregnancy in the Vigo healthcare area from May 2010 to March 2011 were systematically screened for study entry. Patients with overt hypothyroidism and hypothyroidism diagnosed before pregnancy were excluded. The resulting sample consisted of 68 patients. All these patients received iodine replacement therapy...