If hypotension results, the mother feels dizzy and sick, so women usually learn to avoid postures that result in this effect as pregnancy advances. This syndrome is known by several names – aortocaval compression and supine hypotension are common names.

Aortic compression may predominate. Maternal blood pressure is normal or raised if measured above the level of compression, but dramatically reduced below that level.

The blood supply to the uterus (see Page 8), and therefore the fetoplacental unit, originates below the level of aortic compression. Fetal compromise may occur without maternal hypotension.

Note that the azygos venous system is dilated when the IVC is compressed, leading to engorgement of veins within the spinal canal.