Which of the following component is transferred from mother to fetus through placenta?

RRB Nsg. Superintendent -29 April-2025 (shift-2nd)

Obstetrics & Gynaecology

Easy

Appeared in: RRB Nsg. Superintendent -29 April-2025 (shift-2nd)

Explanation

Immunoglobulin G (IgG) is the only antibody class that is actively transported across the placenta from the mother to the fetus.
This process provides the newborn with natural passive immunity, offering protection against infections during the first few months of life.
The transfer is facilitated by specific neonatal Fc receptors (FcRn) on the placental cells, which bind to IgG and transport it across.
This transfer begins around 16 weeks of gestation but increases significantly during the third trimester.

Option A: Platelets are cellular components of blood and are too large to cross the placental barrier.
Option C: White blood cells (leukocytes) are key components of the immune system but are cellular and too large to pass through the placenta.
Option D: Red blood cells (erythrocytes) are responsible for oxygen transport but are cellular and too large to cross the placental barrier. The mixing of maternal and fetal RBCs is abnormal.

Visual 1: Diagram - A diagram illustrating the placental barrier, showing the selective transport of small molecules like IgG via FcRn receptors, while large cells like RBCs, WBCs, and platelets are blocked.
Visual 2: Table - A comparative table of immunoglobulin classes (IgG, IgA, IgM, IgE, IgD), highlighting their size, function, and ability (or inability) to cross the placenta.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Placental transfer and passive immunity as background academic context rather than a clinical decision trigger.
Understanding that only IgG crosses the placenta is crucial for neonatal care. It explains why newborns have temporary protection against diseases their mothers are immune to.
This concept is the basis for understanding Rh incompatibility. An Rh-negative mother can produce anti-Rh IgG antibodies that harm an Rh-positive fetus, leading to Hemolytic Disease of the Newborn.
A nurse should be aware that preterm infants, especially those born before the third-trimester peak of IgG transfer, have lower levels of maternal antibodies and are more vulnerable to infections.

How to Approach the Question

First, identify the core concept of the question, which is the function of the placenta as a selective barrier between mother and fetus.
Recall the different types of substances in the blood: cellular components (RBCs, WBCs, platelets) and plasma components (proteins like immunoglobulins).
Remember the general rule that large structures, especially whole cells, do not cross the placental barrier.
This rule eliminates platelets, white blood cells, and red blood cells as possible answers.
Consider the immunoglobulins. Recall that there are different classes (IgG, IgM, IgA, etc.) with different sizes and functions. Remember the specific exception that IgG is actively transported across the placenta to provide passive immunity.
Select Immunoglobulin G (IgG) as the correct component that is transferred.

Concept Tested & Keywords

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