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. 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). 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). 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.