Recurrent pregnancy loss (RPL) is defined as ≥ 2 failed clinical pregnancies (ACOG), affecting 1-2% of couples. Etiologies: (1) Genetic: parental balanced translocations (3-5%) producing unbalanced gametes; (2) Anatomical: uterine septum (most common surgically correctable cause), submucosal fibroids, Asherman syndrome, cervical insufficiency; (3) Antiphospholipid syndrome: lupus anticoagulant, anticardiolipin, anti-beta-2-GP1 antibodies causing placental thrombosis — the most important TREATABLE cause, requiring aspirin + heparin; (4) Endocrine: uncontrolled diabetes, thyroid disease, PCOS; (5) Thrombophilia: Factor V Leiden, prothrombin mutation associated with late losses; (6) Unexplained (50%) — reassuringly, these couples have 60-75% success with supportive care alone.