Aortocaval compression is thought to be the cause of supine hypotensive syndrome. Supine hypotensive syndrome is characterized by pallor, bradycardia, sweating, nausea, hypotension and dizziness and occurs when a pregnant woman lies on her back and resolves when she is turned on her side.
The aorta and inferior vena cava are central vessels, the largest artery and vein. They supply blood to the heart, and the rest of the body. Thus, when there is compression due to the weight of the fetus, signs of shock (sweating, pallor, fast and weak pulse) may be experienced. The best way to prevent or immediately treat this is to place a rolled up towel or wedge under the right hip, so that the central weight is tilted at least fifteen degrees. Giving water and oxygen and placing cold towels on the forehead will help relieve symptoms of faintness. The legs should immediately be raised above the head (Trendelenberg position) to increase venous return of blood to the heart, such as in a chair.