Comprehensive and Detailed Explanation From Exact Extract–Based NCC C-EFM References:

NCC physiology content specifically includes maternal autoimmune influences on fetal cardiac conduction. Conditions such as maternal lupus (SLE) or Sjogren’s syndrome may produce anti-Ro/SSA and anti-La/SSB antibodies. These antibodies cross the placenta and damage fetal conduction tissue.

The primary site of injury is the fetal atrioventricular (AV) node, leading to:

First-, second-, or complete third-degree heart block

A slow, regular ventricular rate typically 50–70 bpm

Loss of beat-to-beat variability because ventricular myocardium does not display normal autonomic modulation

This mechanism is extensively described in AWHONN, NCC physiology materials, and maternal–fetal physiology texts.

Option A: Antibodies do not target fetal RBCs; that describes hemolytic disease of the newborn.

Option B: Targeting maternal WBCs is not fetal-specific.

The correct affected structure is the fetal AV node.

Therefore, the correct answer is C. The fetal atrioventricular node.