Cardiac output is greatest when?

Cardiac output is greatest when?

• A. During the first trimester of pregnancy
• B. During the second trimester of pregnancy
• C. During the third trimester of pregnancy
• D. Immediately after delivery of the newborn

Answer: (D)

The main idea is that cardiac output hinges on how much blood returns to the heart (preload) plus heart rate and contractility. During pregnancy, blood volume expands and heart rate rises, so CO is elevated. But the highest CO occurs during labor and immediately after delivery because venous return to the heart surges: contractions of the uterus autotransfuse blood from the placental bed back into the maternal circulation, the placental circulation is removed, and relief of the gravid uterus’ compression of the inferior vena cava further increases venous return. This spike in preload, combined with the still-elevated heart rate, pushes cardiac output to its peak right after delivery. After this immediate postpartum period, CO gradually returns toward pre-pregnancy levels over weeks. So, the timing when CO is greatest is immediately after delivery of the newborn.

The main idea is that cardiac output hinges on how much blood returns to the heart (preload) plus heart rate and contractility. During pregnancy, blood volume expands and heart rate rises, so CO is elevated. But the highest CO occurs during labor and immediately after delivery because venous return to the heart surges: contractions of the uterus autotransfuse blood from the placental bed back into the maternal circulation, the placental circulation is removed, and relief of the gravid uterus’ compression of the inferior vena cava further increases venous return. This spike in preload, combined with the still-elevated heart rate, pushes cardiac output to its peak right after delivery. After this immediate postpartum period, CO gradually returns toward pre-pregnancy levels over weeks.

So, the timing when CO is greatest is immediately after delivery of the newborn.