Transient recurrence of hyperthyroidism after delivery in Graves' disease

Four patients with Graves' disease whose hyperthyroidism was in remission following antithyroid therapy were studied without any treatment during and after pregnancy. In the 8-9th month of pregnancy, they were in a euthyroid state with serum levels of thyroxine (T4) of 18.9, 11.9, 11.2 and 14.5 mug/100 ml, triiodothyronine (T3) of 273, 190, 162 and 244 ng/100 ml and T3 resin sponge uptake (RT3U) of 22, 14, 19 and 16% respectively (normal pregnant range: T4, 7.0-15.0, T3 140-250, RT3U 15-25). At 1-3 months after delivery, hyperthyroidism recurred, as manifested by T4 levels of 17.2, 14.5, 16.7 and 21.7 mug/100 ml, T3 levels of 320, 225, 390 and 464 ng/100 ml and RT3U levels of 34, 34, 43, and 41% respectively (normal non-pregnant range: T4 5.0-12.0, T3 90-190, RT3U 24-37). The recurrence of hyperthyroidism was also demonstrated by serial measurements of serum free T4 and free T3. The thyroid function of all four patients returned spontaneously to the normal range at 4-6 months after delivery. One patient developed hypothyroidism for a short period before regaining the euthyroid state. The titers of serum anti-thyroid microsomal antibodies and levels of serum immunoglobulins decreased during pregnancy and increased transitorily at the time of hyperthyroidism after delivery. Similarly, increases in the levels of thyroid hormones, anti-thyroid antibodies and immunoglobulins were observed transitorily following spontaneous abortion after 4 months' pregnancy in one case. We suggest that the transient recurrence of hyperthyroidism in Graves' disease may be induced by immunological changes after delivery.