Our case study describes a 28-year-old female (G2P1) with a large for gestational age fetus and polyhydramnios in the setting of Type 1 Diabetes Mellitus. She presented initially at 29 weeks’ gestation with right lower leg swelling, significant chest pain and breathlessness. Ultrasound of her lower limbs identified a thrombus in the right popliteal vein, as well as slow venous flow within the right common femoral and superficial femoral veins. She was discharged home on therapeutic enoxaparin, with factor Xa levels being in appropriate range. Five days post discharge, she represented with contractions and was diagnosed with threatened pre-term labour in the setting of a previous caesarean section. At the time, a repeat ultrasound scan showed progression of the deep vein thrombosis into the common femoral vein, despite therapeutic anticoagulation. V/Q scan did not show any ventilation perfusion mismatch, but echocardiogram showed evidence of right ventricular strain. She was managed with intravenous heparin and a supra-renal IVC filter was inserted with view to reduce peri-operative mortality in the setting of caesarean section. A progress scan post delivery revealed complete dissipation of the clot and the IVC filter was removed six weeks post partum. The management of progressive deep vein thrombosis despite therapeutic anticoagulation in the setting of threatened pre-term labour in a high risk pregnancy is challenging and requires a multidisciplinary approach.