What is a sign that a pregnant woman may be experiencing a significant volume loss during the third trimester?

The statement regarding the absence of significant signs before a 40% loss of circulating volume refers to the body's physiological responses during pregnancy. In the third trimester, women undergo considerable hemodynamic changes where blood volume increases by about 40-50%. This adaptation helps support both the mother and the developing fetus.

If a pregnant woman experiences significant volume loss, symptoms may not become apparent until a large proportion of circulating volume is depleted. The body can initially compensate for this loss, which is why overt signs of hypovolemia are often not present until the volume loss is considerable, typically around the 40% mark. Therefore, this lack of noticeable signs before such a significant volume loss illustrates the body's remarkable ability to maintain homeostasis during pregnancy until a critical threshold is reached.

Recognizing this concept is essential for health practitioners to monitor and manage complications effectively, ensuring both maternal and fetal well-being.