Physiologic changes of pregnancy
| Arterial compliance increases throughout pregnancy |
| Cardiac output begins to increase by 5 weeks and plateaus at 20 weeks |
| Heart rate increases throughout pregnancy |
| Systolic blood pressure increases at 20 weeks |
| Systemic vascular resistance decreases early on, continues to decrease, and plateaus toward the end of pregnancy |
| Stroke volume peaks at 24 weeks |
| Relative anemia: Red blood cell mass increases but relatively less than plasma volume, which expands by 10% to 15% by 6–12 weeks |
| During labor: Cardiac output increases 15% to 50% with contractions, and circulating volume increases |