HESI Maternity Case Study Practice Test

Blood volume expands during pregnancy to support placental and fetal needs and to prepare for blood loss at delivery. This rise comes mainly from a large expansion of plasma volume, driven by hormonal changes that promote sodium and water retention, so plasma grows more than the red cell mass. By about 32 weeks, the total increase is typically around 1,500 mL above pre-pregnant levels—roughly a 40–50% rise from baseline. This substantial increase supports uteroplacental perfusion and leads to the mild dilutional anemia seen in pregnancy. Therefore, about 1,500 mL is the best estimate for this stage. Smaller increases like 500 mL or 1,000 mL are not enough to meet the demands, while 2,000 mL would be larger than usual for this time.