This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular System, Subject name: Gynaecology & Obstetrics
Cardiac output return to normal how many days after delivery: 
Select and explain. 
A. 1 hour, B. 4 hours, C. 2 weeks, D. 4 weeks
D: 4 weeks
Answer: D: 4 weeks 
Explanation: Ans. D. 4 weeks* The cardiac output (CO) starts to increase from 5th week of pregnancy, reaches its peak 40-50% at about 30-40 weeks.* CO is lowest in the sitting or supine position and highest in the right or left lateral or knee chest position.* It increases further during labor (+50%) and immediately following delivery (+70%) over the pre-labor values.* Within 1-2 hours following birth, the cardiac output is estimated to be about 500ml/min and Hr 120-140/min* CO returns to pre labor values one hour after delivery.* It returns to the pre-pregnancy level in 4 weeks' time.