Published by TDP on February 18, 2024 Deep vein thrombosis (DVT) is a condition where blood clots form in the deep veins of the legs. During pregnancy, the risk of developing DVT increases because of changes in blood circulation and clotting factors. This is because the growing uterus can put pressure on the veins in the pelvis, slowing down blood flow from the legs and increasing the risk of clot formation.