I just returned from the Endocrine Society meetings where the guidelines for treatment of thyrotoxicosis (hyperthyroidsm) and thyroid replacement in pregnancy were discussed. I will focus on goals for treatment in women who have Hashimotos (positive TPO- AB, or thyroid peroxidase antibodies), which are different than for women who do not have such antibodies.
For women with Hashimotos data suggests that maintaining TSH < 2.5 mIU/L and giving some thyroid hormone to those with TSH > 4.0 mIU/L and also to those still in the “normal range” of 2.5-4.0 mIU/L helps decrease miscarriage rate and premature delivery rate, but does not have an impact on future IQ of baby.
There is greater emphasis in trying to achieve pregnancy specific TSH reference ranges for women who are hypothyroid and/or have Hashimotos thyroiditis:
First trimester: 0.1-2.5 mIU/L
Second trimester: 0.2-3.0 mIU/L
Third trimester: 0.3-3.0 mIU/L
Data on the effectiveness of thyroid replacement is not so certain for women who seek fertility and also have Hashimotos. There is insufficient data to know if giving thyroid hormone to these women who are already in the “normal range” will enhance fertility.
For women who do not have Hashimotos there are no current recommendations for either fertility or pregnancy treatment, even if the TSH is above the normal range (4.5-10 mIU/L, subclinical hypothyroid), the ATA has no recommendations due to lack of data. However one can consider replacement in these women for TSH 5-10 range.
My current take on this, until more data is available is that I will try to keep individuals in the “normal range” and make sure nutrition is excellent. Keep adequate iodine replacement for pregnancy which is about 250 mcg/day. This is why a 150mcg Iodine supplementation is in the comprehensive prenatal vitamins.