A pregnant woman in the third trimester performing pelvic floor exercises in the supine position reports dizziness, nausea, and shortness of breath. Which effect best describes the contribution of supine positioning?

• A. Increase in inferior vena cava pressure and increase in venous return and cardiac output
• B. Decrease in inferior vena cava pressure and increase in venous return and cardiac output
• C. Increase in inferior vena cava pressure, leading to a decrease in venous return and cardiac output
• D. Decrease in inferior vena cava pressure, leading to a decrease in venous return and cardiac output

Answer: (C)

In the late stages of pregnancy, lying flat on the back lets the enlarged uterus press against the inferior vena cava. This compresses the vessel, raising the pressure within the IVC and making it harder for blood to return to the heart. With less venous return, the heart’s pumping output drops, which can produce dizziness, nausea, and shortness of breath due to reduced blood flow and oxygen delivery. So the best description is that supine positioning increases IVC pressure, leading to decreased venous return and cardiac output. This is why alternatives that imply increased venous return or decreased IVC pressure don’t fit the presentation.