Which immunoglobulin crosses the human placenta in significant quantities to provide passive immunity to the fetus?

• A IgM, transported by pinocytosis across trophoblast
• B IgE, transported bound to mast cell mediators
• C IgA, transported through paracellular channels in syncytiotrophoblast
• D IgG, transported by an active Fc receptor mediated process ✓

Explanation

Maternal IgG is actively transported across the syncytiotrophoblast via Fcγ receptors (neonatal Fc receptor pathway), reaching higher concentrations in fetal than maternal blood by term. This transfers immunity against tetanus, diphtheria and other antigens. IgM does not cross the placenta at all, which is why elevated fetal IgM suggests intrauterine infection, and neither IgA nor IgE crosses in significant amounts.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.