Rh Disease in Subsequent Pregnancies: Why Risk Increases and How to Prevent It

Rh disease (HDFN) risk increases with each subsequent Rh+ pregnancy in a sensitized Rh− mother.

Mechanism

• 1st Rh+ pregnancy: Sensitization at delivery (or earlier); usually no disease (IgM doesn’t cross placenta).
• Subsequent pregnancies: Memory B cells → rapid anti‑D IgG production → crosses placenta → fetal hemolysis.
• Each exposure ↑ titer, ↑ severity, earlier onset.

Prevention Protocol

• RhoGAM (RhIg) 300 μg IM at 28 weeks + within 72 hours post‑delivery (if baby Rh+).
• Also after: miscarriage, abortion, ectopic, amnio, CVS, bleeding, trauma, ECV.
• Postpartum dose even if infant Rh− (conservative).

If Already Sensitized

• RhIg ineffective.
• Monitor: monthly titers, MCA Doppler q1–2 weeks from 18–20 weeks.
• IUT for anemia; delivery at 34–37 weeks if severe.

Universal Rh screening + timely RhIg = near‑elimination of Rh HDFN.