Planning pregnancy with subclinical hypothyroidism

How to manage a woman with subclinical hypothyroidism who is planning a pregnancy? Is this management different in a woman in the first trimester of pregnancy?

Leonard Wartofsky, MD: In a woman planning pregnancy, I would want to ensure that the thyroid function vis-a-vis thyroid-stimulating hormone (TSH) levels were optimal for conception. Based on data indicating a normal young woman would have an average TSH between 1.3 and 1.6 mIU/L, I would want to have that young woman in that TSH range. If the TSH were higher, I would add thyroxine replacement to bring it down, but not too low, not to suppress, because infertility is associated with hyperthyroidism. So one would target that narrow TSH range, which we can do with thyroxine that comes in multiple dosage strengths. We can titrate it fairly precisely.

During pregnancy one would adjust any thyroxine therapy to stay within the ranges that are noted for pregnancy—again, perhaps no higher than a TSH level of 2.6, 2.7 mIU/L throughout all 3 trimesters.