The volume of blood in a mature placenta is about?

Appeared in: UPRVUNL - 2021

Explanation

The total blood volume in a mature placenta at term is approximately 500 mL.
This volume is composed of both maternal and fetal blood, which do not mix.
The maternal component, about 150 mL, circulates in the intervillous space.
The fetal component, about 350 mL, is contained within the capillaries of the chorionic villi.

Option B: This value is too high. A volume of 1000 mL is more commonly associated with the average blood loss during a cesarean section, not the volume contained within the placenta itself.
Option C: This value is incomplete. 150 mL represents only the volume of maternal blood in the intervillous space, not the total blood volume of the placenta.
Option D: This value is an underestimation of the total combined maternal and fetal blood volume within the placenta.

Clinical Relevance

Nursing practice connection: Knowing Physiology of Placental Blood Volume helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Knowledge of placental blood volume is critical for managing the third stage of labor and anticipating the risk of postpartum hemorrhage (PPH).
In a placental abruption, the amount of blood lost can be significant, as it involves hemorrhage from this uteroplacental circulation, which can rapidly compromise both maternal and fetal status.
What if? If a patient has placentomegaly (an abnormally large placenta), as seen in conditions like uncontrolled maternal diabetes or fetal hydrops, the total placental blood volume is increased. This elevates the risk for severe PPH when the placenta separates.

How to Approach the Question

This is a factual recall question based on obstetric physiology.
Identify the core concept being tested: the total blood volume in a mature placenta.
Recall the standard physiological value from textbook knowledge.
Differentiate the total volume from its individual components (maternal and fetal).
Evaluate the options. Eliminate those that represent only a partial volume (e.g., 150 mL for the maternal portion) or are significant over/underestimations.
Select the option that matches the accepted value for the total placental blood volume.

Concept Tested & Keywords

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E6 Obstetrics Williams p. 22-41

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