RESUMEN
AIM: To clarify dynamic changes of IgG subtypes of thyroid peroxidase antibody (TPOAb) during the first postpartum year in Chinese patients diagnosed with postpartum thyroiditis (PPT). METHODS: We retrospectively collected serum samples before and 3, 6, 9 and 12 months postpartum from 58 PPT patients. Levels of TPOAb and its IgG subtypes were examined by ELISA. RESULTS: Titers of total TPOAb and its IgG subtypes were lowest before delivery in PPT patients. Following delivery, titers of total TPOAb increased. Concentrations of IgG1 and IgG4 subtypes increased for 3 months postpartum, then became stable. Concentrations of the IgG2 subtype increased gradually until 9 months postpartum. Concentrations of the IgG3 subtype reached a peak at 6 months postpartum and remained at a high level thereafter. In PPT patients with an episode of hypothyroidism, levels of total TPOAb and of the IgG subtypes as well as the IgG1/IgG4 ratios were significantly higher than those in patients with an episode of hyperthyroidism and normal controls. Correlations between titers of TPOAb and thyroid-stimulating hormone levels (positive) and free T(4) levels (negative) were seen 6 months postpartum. CONCLUSION: TPOAb is related to thyroid injury and the IgG1 subtype of TPOAb may play a major role in the damage of the thyroid in PPT.