Redness in the calves of pregnant women is not necessarily the cause of thrombosis. However, it should be noted that the special group of pregnant women is indeed at high risk for lower extremity vein thrombosis. When thrombosis forms in the veins of the lower extremities, the skin of the lower extremities becomes red in color, the skin temperature increases, swelling, and pain, but it is not possible to decide, because of one of these phenomena, whether there is thrombosis or not. When lower extremity vein thrombosis is suspected, it is recommended to visit a specialized vascular surgery clinic and perform ultrasonography to clarify the diagnosis. Under ultrasonography, it is possible to clearly see whether there is a thrombus in the vein and whether there are side branches in the area where the thrombus is formed, etc. If a pregnant woman does have venous thrombosis, anticoagulation with low molecular weight heparin is currently recommended only during pregnancy, due to the specific nature of some drug applications. The application of some other drugs is not recommended during pregnancy.