Thyroid inflammation during pregnancy, particularly Hashimoto's thyroiditis (HT) and postpartum thyroiditis (PPT), has a strong genetic and epigenetic basis. Susceptibility to these conditions is associated with specific HLA haplotypes (HLA-DR3, DR4, DR5) and immune-regulatory genes, including CTLA-4, PTPN22, FOXP3, as well as thyroid-specific genes such as TSHR, TG, and TPO. CTLA-4 polymorphism (CT60) is linked to increased thyroid autoantibody production, while PTPN22 R620W variant disrupts immune tolerance, exacerbating autoreactive lymphocyte activation.Epigenetic modifications play a crucial role in HT and PPT pathogenesis. Dysregulation of microRNAs (miRNAs), including miR-146a, miR-142, miR-301, and miR-155, affects immune pathways by modulating T-cell responses and inflammatory cytokine production. Aberrant DNA methylation in genes regulating immune function, such as FOXP3 and CTLA-4, contributes to altered immune tolerance and disease progression.Oxidative stress further modulates disease severity by inducing DNA damage and enhancing inflammatory responses, particularly in pregnancy. Reactive oxygen species (ROS) promote thyroid autoimmunity by affecting placental function and fetal neurodevelopment. Understanding the interplay between genetic susceptibility, epigenetic regulation, and oxidative stress is essential for developing personalized management strategies. This review highlights the molecular mechanisms underlying HT and PPT and the potential of epigenetic biomarkers for early diagnosis and targeted therapies.