Treatment with fixed thyroxine doses in pregnant women with subclinical hypothyroidism.

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 50 mcg/day. TSH measurements were performed to assess the need to change the dose, which was increased or decreased by 25 mcg/day when necessary.

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

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