Rh Incompatibility: First Pregnancy Usually Unaffected
RhD-negative mother + RhD-positive fetus → risk of alloimmunization. First pregnancy is rarely affected because:
- Fetomaternal hemorrhage (FMH) sufficient for sensitization usually occurs at delivery.
- Maternal anti-D IgG crosses placenta in subsequent pregnancies → hemolytic disease of fetus/newborn (HDFN).
Prevention
- Routine RhD typing at booking.
- Anti-D prophylaxis: 28 weeks (1500 IU) + within 72 hrs of delivery/sensitizing event (amnio, trauma, bleeding).
- Postpartum: test cord blood; if RhD+, give anti-D.
Monitoring
If sensitized (positive antibody screen): serial antibody titers, MCA Doppler for fetal anemia, intrauterine transfusion if needed.
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