DVT or blood clots in your vascular system can be life threatening if they occlude a vessel to your heart, brain, or lungs. Pregnancy, obesity, smoking, immobilization, cancer, and recent surgery are all risk factors for developing a blood clot. The incidence of a venous blood clot in pregnancy is 0.5-3 per 1000 pregnancies, and it occurs equally in all trimesters. The hormone shifts of pregnancy change the production of substances that promote and dissolve blood clots leading to thickened blood, or hypercoagulation. Because of the expanded blood volume during pregnancy, blood moves through the veins less rapidly leading to a state called venous stasis. You can imagine how blood that moves slowly is more likely to clot.