Physiologic Changes During Normal Pregnancy and Delivery
Introduction
Soon after conception, the maternal cardiovascular system undergoes major adaptations that progress throughout gestation. In conjunction with the increased circulatory burden of pregnancy, these changes may unmask previously unrecognized heart disease and result in significant morbidity and mortality. Most of these changes are almost fully reversed in the weeks and months after delivery.
Section snippets
Blood Volume
Blood volume increases significantly during pregnancy. The increase starts at around 6 weeks' gestation and reaches a maximal volume of 4700 to 5200 mL by 32 weeks' gestation.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 A rapid increase is typically noted until midpregnancy, with a slower increase thereafter (Fig. 1).6 Overall, a continuous blood volume increase of about 45% (1200–1600 mL), or a mean recorded blood volume ranging from 73 to 96 mL/kg greater than
Cardiocirculatory changes during labor and delivery
Women with cardiac disease require close monitoring during labor and delivery. Uterine contractions alone can transfer 300 to 500 mL of blood from the uterus to the general circulation and lead to significant circulatory stress.161, 162, 163, 164
Hemodynamic effects of cesarean section
Transient maternal hypotension can occur in up to 30% of women undergoing regional anesthesia for cesarean section,74 but most women undergoing cesarean section under epidural anesthesia remain stable hemodynamically. BP typically declines moderately after anesthesia induction, but then remains constant. In addition, HR, CO, and stroke volume remain constant. Following delivery, CO increases about 25% more than baseline, with a stable HR. In contrast, cesarean section under spinal anesthesia is
Hemodynamic changes postpartum
A 60% to 80% increase in CO occurs immediately after delivery, followed by a rapid decrease within 10 minutes to values approaching normal 1 hour postpartum. In addition, SVR decreases.163, 164, 178, 181, 182 This high output state is likely caused by the transfer of blood from the uterus into the systemic circulation (autotransfusion) in conjunction with improved venous return caused by decreased vena caval compression and the rapid mobilization of extracellular fluid. Placental separation in
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Disclosures: None.