What are the current recommendations regarding > treating Hashimoto's during pregnancy? How frequently should the woman be monitored with thyroid tests? Should she be followed a high risk OBGYN?
Dr. Amy Handler, Katonah, NY
This question demands an answer subdivided in several parts. Concerning thyroid function, most patients (but not all) with Hashimoto's disease already take l-T4 before pregnancy (this was not specified in the question asked). - If it is the case, thyroid function tests should be carried out rapidly after conception (say, within 8-10 weeks and no later than 12 wks) and the l-T4 dosage adapted. Depending on the functional capabilities of the thyroid gland to adapt to the increased hormonal demands during gestation (see article by Mike Kaplan in Thyroid), the daily dosage should be increased (usually by 30-60 % eventually, above preconception dosage), but it is important to note that the l-T4 increment may vary widely individually. The main objective in these early stages is to avoid a raise in serum TSH and obviously a fall in free T4 (risk for the fetal development, etc). After this early adaptation, we check thyroid function in such patients every 2 months until 5-6 months gestation. Thereafter the dosage usually remains unchanged until parturition. - If this Hashimoto patient does not yet require l-T4 before pregnancy because she is euthyroid, I suggest to follow the algorithm that I have proposed in 1998 (see Trends in Endocrinology & Metabolism, vol. 9; NÂ° 10; December 1998). In this scheme, we base our attitude on the titers of thyroid antibodies and serum TSH levels (when these are still within normal range) to decide whether to treat or monitor. If l-T4 treatment is given, the buckle rejoins the first option discussed above. If l-T4 treatment is not warranted (TSH below 2.5 mU/L; low Ab titers; normal free T4 around mid-gestation), we later monitor thyroid function tests (TSH and free T4) around 27-28 and 34-35 weeks gestation. - An additional difficulty could be those (extremely rare) patients who would only have a low-normal free T4 without serum TSH elevation during early gestation. We don't encounter such patients (but others do ??) and it has been proposed by some authors to give the mother (and perhaps the fetus ?) the potential benefit of l-T4 treatment in such instances. - In all cases patients with Hashimoto's disease should see an endocrinologist during and after the pregnancy (because of the risk of postpartum thyroiditis). During pregnancy, we follow these patients in close collaboration with the ObGyn, but high risk ObGyn is not mandatory (in my opinion). - It should also be remembered that Hahimoto's patients have an increased risk of early miscarriage (see article by Poppe et al. in Thyroid, November 2002 and a review in press by Glinoer in Human Reproduction Update). This risk could justify the opinion of a "high risk ObGyn", even though there is not much that can presently be done to reduce the miscarriage risk (except to have a normal thyroid function, probably ?); in rare cases trials have been initiated using steroids or iv IG (in women with recurrent abortions).
Prof Daniel Glinoer