Effect of Thyroid Peroxidase Antibody Titers Trajectories during Pregnancy and Postpartum on Postpartum Thyroid Dysfunction

Abstract Objective To identify risk factors contributing to the development of postpartum hypothyroidism in women newly diagnosed with subclinical hypothyroidism (SCH) during the first trimester of pregnancy (T1). Additionally, this study aimed to explore the impact of thyroid peroxidase antibody (TPOAb) titers trajectories throughout pregnancy and postpartum. Methods Thyroid hormone levels and thyroid autoantibody titers were collected from T1 to the 12th month postpartum. Logistic regression analysis was employed to identify independent risk factors for hypothyroidism at the 12th month postpartum and to develop a prediction model. Model performance was assessed through discrimination, calibration and clinical applicability, with internal validation using the bootstrap resampling method. Growth Mixture Modeling was applied to delineate the trajectory of TPOAb titers during pregnancy and postpartum, logistic regression analysis was conducted to investigate the influence of these trajectories on the occurrence of postpartum hypothyroidism. Results At the 12th month postpartum, hypothyroidism was either newly diagnosed or persisted in 76 of 209 cases (36.36%). Several significant risk factors for postpartum hypothyroidism were identified, including multiparity, positive TPOAb in T1, positive TPOAb and thyroglobulin antibody in T1, serum thyroid-stimulating hormone levels at SCH diagnosis in T1, and the final dose of levothyroxine in the third trimester. A prediction model was constructed and presented with a nomogram. Furthermore, a higher trajectory of serum TPOAb titer during pregnancy and postpartum emerged as a predictive factor for hypothyroidism at the 12th month postpartum. Conclusion Women with elevated TPOAb titers during pregnancy and postpartum necessitate ongoing and vigilant monitoring of thyroid function, even after childbirth.