Only immunoglobulin which can cross the placenta is?

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2018

Explanation

Immunoglobulin G (IgG) is the only antibody class that is actively transported across the human placenta.
This transfer is facilitated by the neonatal Fc receptor (FcRn) on placental cells, primarily during the third trimester of pregnancy.
Maternal IgG provides the fetus and newborn with passive immunity, offering protection against infections for the first several months of life.
This mechanism is also responsible for conditions like Rh isoimmunization, where maternal IgG antibodies can attack fetal red blood cells.

Option A: IgA does not cross the placenta. It is the primary antibody found in mucosal secretions.
Option B: IgM is a large pentameric molecule and is too big to cross the placental barrier.
Option D: IgE does not cross the placenta. It is primarily involved in allergic reactions and defense against parasites.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Maternal-Fetal Immunology and Placental Transfer of Immunoglobulins as background academic context rather than a clinical decision trigger.
A key nursing role is educating expectant mothers about the importance of third-trimester vaccinations (like Tdap) to maximize the transfer of protective IgG antibodies to the fetus.
Nurses in neonatal units must be aware that preterm infants have lower levels of maternal IgG and are therefore at a higher risk for infections, requiring stricter infection control measures.
Understanding this concept is crucial for managing Rh-negative pregnant women. Nurses administer Rho(D) immune globulin (RhoGAM), which is an IgG preparation, to prevent the mother from forming her own anti-D IgG that could harm a future Rh-positive fetus.

How to Approach the Question

First, identify the core of the question, which is about the transfer of immunoglobulins across the placenta.
Recall the five major classes of immunoglobulins: IgG, IgA, IgM, IgE, and IgD.
Access your knowledge about the specific functions and properties of each class. Remember key characteristics like size and primary location.
Associate IgG with its unique ability to cross the placenta. A helpful mnemonic is 'IgG Goes across the placenta'.
Consider the other options: IgM is too 'massive' (a pentamer) to cross. IgA is the 'secretory' antibody (in milk). IgE is for 'allergy' and 'eosinophils'.
Based on this specific recall, select IgG as the only immunoglobulin that crosses the placental barrier.

Concept Tested & Keywords

Concept Tested: Maternal-Fetal Immunology and Placental Transfer of Immunoglobulins
Stem keywords: immunoglobulin, cross, placenta
Lead-in keywords: Only
Negative lead-in flag: false

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Practise the full RUHS, Jaipur, PB B.Sc Nursing Entrance-2018

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