Maximum cardiac output is seen in which week of pregnancy?
Ans. c. 28 weeks (Ref: Dutta 6/e p52, 53)Maximum cardiac output among the given options is seen in 28th week of pregnancy. Though, maximum increase in cardiac output is seen in 32nd week of pregnancy (not given in the option).'Cardiac output increases from the fifth week of pregnancy and reaches its maximum levels at approximately 32 weeks, after which there is only a slight increase until labor, delivery, and the postpartum period.'- Miller Anesthesia 7th/chapter 69Physiological Changes in the Cardiovascular System During PregnancyPeripheral vasodilation leading to a decrease in systemic vascular resistance is thought to be the first cardiovascular change associated with pregnancy (induced by progesterone).Cardiac output increases in response to this, by 20% at 8 weeks gestation and by up to 40-50% at 20-28 weeks gestation.This is achieved predominantly via an increase in stroke volume (due to an increase in ventricular end-diastolic volume, wall muscle mass, and contractility) but also by an increase in heart rate.Labour leads to further increases in cardiac output by 15% in the first stage and 50% in the second stage due to the combination of auto-transfusion of 300-500 ml of blood back into the circulation with each uterine contraction, and sympathetic stimulation caused by pain and anxiety.Cardiac output increases again immediately after delivery due to auto-transfusion of blood via uterine contraction and relief of aortocaval compression. This may increase cardiac output by as much as 60-80%, followed by a rapid decline to pre-labour values within 1 hour.
24 weeks
20 weeks
28 weeks
22 weeks
Cardiovascular System