During CPR on a pregnant patient, after manually displacing the uterus to the left, return of spontaneous circulation occurs. What explains this most likely?

• A. Increased blood flow to her heart caused her ventricles to stop fibrillating
• B. Pressure was relieved from her aorta and vena cava, which improved chest compression effectiveness
• C. Displacement of her uterus caused blood flow backward, which increased blood flow to her heart
• D. Displacement of her uterus allowed her lungs to expand more fully, which restored her pulse

Answer: (B)

When a pregnant patient is in the later stages of pregnancy, lying on the back can cause the enlarged uterus to press on the aorta and inferior vena cava. This compresses the great vessels, reducing venous return to the heart and making chest compressions less effective. By displacing the uterus to the left, that pressure is relieved, improving venous return (preload) and the effectiveness of CPR. With better preload and forward flow, circulation can improve enough to restore spontaneous circulation. While improved ventilation from more lung expansion can help oxygen delivery, the key reason for the ROSC in this scenario is the relief of aorto-caval compression that enhances venous return and chest compression efficacy.