Recurrent Pregnancy Loss Despite Therapeutic Anticoagulation in a Patient With May-Thurner Syndrome: A Case Report.

Pregnancy is a hypercoagulable state associated with an increased risk of venous thromboembolism. May-Thurner syndrome (MTS), an anatomic compression of the left common iliac vein by the right common iliac artery, predisposes affected individuals to left-sided deep vein thrombosis (DVT) and is often underrecognized in pregnant patients. While maternal thrombotic complications related to MTS have been described, its potential impact on fetal outcomes remains poorly characterized. We report the case of a 29-year-old gravida 7, para 2 woman with confirmed MTS and recurrent pregnancy-associated left lower extremity DVTs who experienced multiple adverse obstetric outcomes, including fetal growth restriction and recurrent fetal demise. Despite negative hypercoagulable testing and adherence to therapeutic anticoagulation, the patient developed postpartum and early-pregnancy DVTs and demonstrated a progressive pattern of fetal loss at increasingly earlier gestational ages. Her most recent pregnancy ended in early second-trimester fetal demise while receiving therapeutic low-molecular-weight heparin. This case suggests a clinically relevant association between maternal venous outflow obstruction, recurrent thrombosis, and placental dysfunction. The combination of chronic iliac venous compression and recurrent thromboembolic events may impair uteroplacental venous drainage, contributing to placental insufficiency, fetal growth restriction, and fetal demise. Notably, these outcomes occurred in the absence of systemic thrombophilia, suggesting a predominantly anatomic and physiologic mechanism.