Which of the following statements is NOT true regarding Anti-D immunoglobulin?

NORCET 9 Prelims-2025

Obstetrics & Gynaecology

Medium

Appeared in: NORCET 9 Prelims-2025

Explanation

The standard prophylactic dose of Anti-D immunoglobulin after a normal delivery of an Rh-positive baby is 300 µg, not 100 µg.
A 100 µg dose is insufficient to provide adequate protection against Rh sensitization from the potential volume of fetomaternal hemorrhage that can occur at term.
This dose must be administered to the Rh-negative mother within 72 hours of delivery to be effective.

Option A: This statement is true. For events in the first trimester (before 12 weeks), such as an abortion, a smaller dose of 50 µg is considered sufficient due to the lower risk of significant fetomaternal hemorrhage.
Option C: This statement is technically false. A 300 µg dose of Anti-D neutralizes 30 mL of fetal whole blood, which contains approximately 15 mL of fetal RBCs. However, option B represents a more significant clinical dosage error.
Option D: This statement is true. While a 50 µg dose is sufficient for a first-trimester abortion, administering the standard 300 µg dose is also a safe and common practice, particularly if the smaller dose is unavailable.

Visual 1: Infographic - A chart summarizing the correct dosages and indications for Anti-D immunoglobulin administration throughout pregnancy and postpartum, highlighting the different doses for first trimester, later trimesters, and post-delivery.
Visual 2: Diagram - An illustration showing the mechanism of Rh sensitization, where an Rh-negative mother is exposed to Rh-positive fetal red blood cells, and how Anti-D immunoglobulin works to prevent the mother from forming her own antibodies.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Dosage and indications for Anti-D immunoglobulin administration in obstetrics as background academic context rather than a clinical decision trigger.
Administering the correct dose of Anti-D immunoglobulin is critical for preventing Rh alloimmunization in Rh-negative mothers.
Failure to provide an adequate dose can lead to the mother developing anti-D antibodies, which can cross the placenta in subsequent pregnancies and cause hemolytic disease of the fetus and newborn (HDFN), a potentially fatal condition.
What if? If a massive fetomaternal hemorrhage (greater than 30 mL of fetal whole blood) is suspected, a Kleihauer-Betke (KB) test is performed to quantify the amount of fetal blood in the maternal circulation. The dose of Anti-D is then adjusted accordingly, with one 300 µg dose given for every 15 mL of fetal RBCs (or 30 mL of whole blood) detected.

How to Approach the Question

First, identify the core concept: the question is testing knowledge of Anti-D immunoglobulin dosages and indications.
The lead-in 'NOT true' requires you to evaluate each statement for accuracy. This means three statements will be true, and one will be false.
Carefully read each option, recalling standard clinical guidelines for Anti-D administration.
Evaluate Option A: Is 50 µg correct for a first-trimester abortion? Yes, this is a standard low dose.
Evaluate Option B: Is 100 µg correct for postpartum? No, the standard dose is 300 µg. This is a likely candidate for the incorrect statement.
Evaluate Option C: Does 300 µg neutralize 30 mL of fetal RBCs? No, it neutralizes 15 mL of RBCs or 30 mL of whole blood. This is also incorrect.

Concept Tested & Keywords

Concept Tested: Dosage and indications for Anti-D immunoglobulin administration in obstetrics.
Stem keywords: Anti-D immunoglobulin, NOT true
Lead-in keywords: NOT true
Negative lead-in flag: The question asks for the statement that is NOT true.

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