During third trimester vaginal bleeding, how much blood volume may a mother lose before signs of hypovolemia appear?

In cases of third trimester vaginal bleeding, a mother may lose about 10% to 20% of blood volume before showing signs of hypovolemia. This is an important point because it highlights the body's compensatory mechanisms during pregnancy, which can mask the initial effects of blood loss.

During pregnancy, a woman's blood volume increases, which helps accommodate the demands of the growing fetus and prepares the body for potential blood loss during delivery. Due to this increased blood volume, the threshold for noticing signs of hypovolemia is elevated. It is only after a loss in this range that a mother might start to experience symptoms like increased heart rate or a drop in blood pressure that are indicative of hypovolemia.

The other options reflect higher percentages of blood volume loss. Losing more than 20% of blood volume typically results in more pronounced clinical signs and symptoms of hypovolemia, which would be concerning and warrant immediate medical attention. Therefore, the correct response accurately represents the confidence interval for blood loss before significant symptoms arise in this specific situation.