UPPSC 2023: All of the following antibodies can cross the placenta,& x20;

UPPSC 2023

Obstetrics & Gynaecology

Easy

Appeared in: UPPSC 2023

Explanation

IgG is the only class of immunoglobulin that is actively transported across the placenta from mother to fetus.
This transfer is facilitated by the neonatal Fc receptor (FcRn) on placental cells.
Due to its relatively small molecular weight and this active transport system, IgG provides passive immunity to the newborn.
This maternal IgG protects the infant from various infections during the first few months of life until its own immune system matures.

Option B: IgA is the primary antibody in mucosal secretions (e.g., breast milk, saliva) and provides local immunity. It is not transported across the placenta.
Option C: IgE is primarily involved in allergic (Type I hypersensitivity) reactions and defense against parasites. It does not cross the placenta.
Option D: IgM is a large pentameric molecule, making it too big to pass through the placental barrier. It is the first antibody produced in an immune response.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Placental transfer of immunoglobulins and passive immunity as background academic context rather than a clinical decision trigger.
The transfer of maternal IgG provides essential passive immunity to newborns, protecting them from infections like measles, rubella, and tetanus in their first few months.
This principle is why vaccinating pregnant women (e.g., with Tdap) is recommended; the protective antibodies are passed to the fetus.
What if the mother has an autoimmune disease like lupus or myasthenia gravis? Pathogenic IgG autoantibodies can also cross the placenta and cause transient disease (e.g., neonatal lupus, transient neonatal myasthenia gravis) in the newborn.

How to Approach the Question

First, recognize that the question, although poorly phrased, is asking to identify the specific antibody class capable of crossing the placenta.
Recall the five major classes of immunoglobulins: IgG, IgA, IgM, IgD, and IgE (mnemonic: GAMED).
Consider the primary function and structure of each class. Remember that size is a critical factor for placental transfer.
IgM is a large pentamer, making it an unlikely candidate. IgA is primarily for mucosal immunity. IgE is for allergies.
Recall that IgG is the most abundant antibody in serum and is known for providing long-term immunity. Its monomer structure and a specific transport system allow it to cross the placenta.
Based on this knowledge, select IgG as the only antibody that crosses the placenta to provide passive immunity to the fetus.

Concept Tested & Keywords

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