Transient hypothyroidism after delivery in autoimmune thyroiditis.

The spontaneous occurrence of, and recovery from primary hypothyroidism were observed after delivery in 6 women with autoimmune thyroiditis. Diffuse goiter was noticed 1-3 months after delivery. The blood thyroid hormone level was found to be lowest at 3-6 months post-partum, with a thyroxine iodine value of 1.0 +/- 0.6 mug/dl (mean +/- SD) (normal 3.0-7.2), triiodithyronine value of 77 +/- 11 ng/dl (normal 90-190) and T3 resin sponge uptake of 21 +/- 2.8% (normal 24-37). During this period the serum level of thyrotropin was increased to 307 +/- 235 muU/ml (normal less than 8) and 131I thyroid uptake in 24 hours was more than 60%. Then 6-9 months after delivery, the enlarged thyroid gland decreased in size, and the values in thyroid function tests returned to the normal range without any treatment. Anti-thyroglobulin antibodies were positive in 3 cases. Anti-thyroid microsomal antibodies were positive in all cases with titers of 1:10(4)-4:10(9), and titers were highest during the period of hypothyroidism and decreased thereafter. We suggest that these transient changes might be induced by pregnancy and delivery during the course of autoimmune thyroiditis.