A 34 years old female has recently been diagnosed with an autoimmune disease. She has also recently discovered that she is pregnant. Which of the following is the only immunoglobulin that will provide protection to the fetus in the womb?

Appeared in: UPUMS Nsg.Officer-2024

Explanation

Immunoglobulin G (IgG) is the only antibody isotype that can cross the placental barrier.
This transfer provides the fetus with passive immunity, offering protection against pathogens that the mother has been exposed to.
IgG has the smallest molecular weight among immunoglobulins, which, along with a specific active transport mechanism involving Fc receptors on placental cells, facilitates its passage.
Maternal IgG antibodies can be detected in the neonatal circulation for several months after birth, providing continued protection.

Option A: IgE is primarily involved in mediating allergic (type I hypersensitivity) reactions and defense against helminthic (parasitic) infections. It does not cross the placenta.
Option B: IgA is the main antibody found in mucosal secretions (saliva, tears, bronchial and intestinal fluids) and is also present in breast milk (colostrum), providing local immunity. It does not cross the placenta.
Option D: IgD is found in very small amounts in the blood and primarily functions as an antigen receptor on the surface of B lymphocytes, helping to initiate the immune response. It does not cross the placenta.

Clinical Relevance

Nursing practice connection: Knowing Placental transfer of immunoglobulins and passive immunity helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding that only IgG crosses the placenta is fundamental for neonatal and maternal care. It explains why newborns have temporary protection against certain infections.
This knowledge is critical in managing pregnancies with Rh incompatibility. Maternal anti-Rh antibodies are IgG and can cause hemolytic disease of the newborn.
What if the question asked about immunity transferred via breast milk? The answer would be IgA, which is abundant in colostrum and protects the infant's mucosal surfaces.

How to Approach the Question

First, identify the core of the question: which antibody provides protection to the fetus in the womb?
This requires recalling the specific functions of the different immunoglobulin classes.
A helpful mnemonic is 'IgG Goes across the placenta'. This immediately points to IgG as the correct answer.
Systematically eliminate the other options by recalling their primary roles: IgA is for mucosal/secretory immunity (including breast milk), IgE is for allergies, and IgD is a B-cell receptor.
Confirm that IgG is the only one with the specific function of placental transfer.

Concept Tested & Keywords

Concept Tested: Placental transfer of immunoglobulins and passive immunity.
Stem keywords: immunoglobulin, protection, fetus, womb, pregnant, autoimmune disease
Lead-in keywords: only immunoglobulin
Clinical cues: A pregnant patient with an autoimmune disease highlights the dual nature of IgG transfer: it provides protection but can also transmit harmful autoantibodies.

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E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart A (pp 26-201 of 604) p. 101-103

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart B (pp 240-463 of 478) p. 92-94

E6 Microbiology Essentials Sastry 4e Part 1 p. 150-152

Practise the full UPUMS Nsg.Officer-2024

Attempt every question from this paper in a timed mock, then review the full solution for each one.