Assessment of serum thyroid hormone autoantibodies in the first trimester of gestation as predictors of postpartum thyroiditis.

BACKGROUND: Measurement of serum thyroperoxidase autoantibodies (TPOAb) during gestation as a classical marker for the risk of postpartum thyroiditis (PPT) predicts PPT in 1/3 to 1/2 of women. Very few studies have measured serum thyroid hormone Ab (THAb) during gestation, and none as a possible marker for PPT. METHODS: In 412 women who were followed up from 7 to 11 weeks of gestation through 12 months after delivery, we measured THAb (T3.IgM, T3.IgG, T4.IgM, T4.IgG), thyroglobulin autoantibodies (TgAb) and TPOAb at study entry (7-11 week of gestation). RESULTS: Sixty-three women (15.3%) developed PPT, which progressed to permanent hypothyroidism (PH) in 34/63 (54%). THAb+ve were 21/412 women (5.1%), the frequency being greater in those who then developed PPT (12/63 [19.0%] vs. 9/349 [2.6%], P = 4.6 × 10-8), and in the PH subgroup (26.5% [9/34] vs. 10.3% [10/29], P = 0.12). THAb positivity occurred in 9/76 women (11.8%) who were TgAb and/or TPOAb+ve compared to 12/336 women who were TgAb and TPOAb negative (3.6%, P = 0.0031). Of these 9 THAb+ve, TgAb and/or TPOAb+ve women, all (100%) developed PPT compared to 3/11 (27.3%, P = 0.0011) THAb+ve, TgAb and/or TPOAb negative women. Of these 9 and 3 PPT women, 8 and 1 progressed to PH (88.9% and 33.3%, respectively, P = 0.12). CONCLUSIONS: Gestational positivity of THAb enhance enormously the predictivity for PPT of gestational positivity of TPOAb/TgAb. However, their low frequency (5.1%) and their sensitivity (17.5% [21/63]) go against their application in lieu of TPOAb/TgAb.

Unexpected Elevated Free Thyroid Hormones in Pregnancy.

BACKGROUND: The use of thyrotropin and free thyroid hormone assays to evaluate thyroid function is widespread, but in some situations the results are inconsistent with the patient's thyroid status. SUMMARY: A 35-year-old woman with a known diagnosis of chronic autoimmune thyroiditis was referred to the authors' clinic at week 26 of her second pregnancy. The patient was clinically euthyroid. Consistent with this, her serum thyrotropin (TSH) was normal (0.79 mIU/L), but she had elevated free thyroid hormones-free triiodothyronine (fT3) and free thyroxine (fT4)-as determined by a one-step chemiluminescent assay. The patient was taking levothyroxine replacement therapy (125 µg/day), and the dose was confirmed. Previous blood tests showed concordance between TSH and free thyroid hormone values. The patient was followed up throughout gestation and at 12 months postpartum. During gestation, her free thyroid hormones remained high using one-step methods, while the total thyroid hormone concentration values were within the reference range, in agreement with the TSH values. Postpartum fT4 and fT3 values returned progressively to normality, in agreement with the TSH values. The presence of circulating thyroid hormone autoantibodies (THAb) was hypothesized, which are known to interfere, although to a variable extent, with thyroid hormone one-step assays. Using stored frozen sera, this hypothesis was confirmed indirectly by measuring normal levels of fT3 and fT4 with a two-step method, and directly by demonstrating THAb against the two hormones. CONCLUSION: Despite their relative rarity, circulating THAb may be suspected when laboratory data are not consistent and contrast with the clinical picture. To the authors' knowledge, no previous case of transient appearance of THAb in pregnancy has been described.