Which maternal position significantly decreases uterine blood flow?

The supine position, where a pregnant individual lies flat on their back, significantly decreases uterine blood flow due to the compression of the inferior vena cava. In this position, the weight of the gravid uterus can compress this major vein, which is responsible for returning blood to the heart. This compression can lead to reduced venous return, resulting in lower cardiac output and, subsequently, diminished uteroplacental perfusion. As a consequence, this can restrict blood flow to the uterus, adversely affecting fetal oxygenation and overall health.

In contrast, the left lateral position is often recommended during pregnancy as it optimally increases blood flow to the uterus by relieving vena cava compression. Similar benefits are experienced in the right lateral position, although the left side is typically preferred. The sitting position may also allow for better blood flow than the supine position, as it reduces pressure on the vena cava compared to lying flat on the back. Thus, among all the options, the supine position poses the greatest risk of decreasing uterine blood flow.