questions 2

Rh Disease

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Topic updated on 11/08/17 4:24pm

Snapshot
  • A 29-year-old woman presents at 28 weeks gestation for a scheduled check-up.  She states that her baby is moving as much as usual and she is feeling well.  On physical exam you see a gravid uterus that extends 28 cm above the pubic symphysis.  Of note this is this mother's first pregnancy.  Her vitals are within normal limits, she is currently taking a multivitamin and folate and her blood type is A negative.  
Introduction
  • Caused when a Rh negative mother carries a Rh positive fetus
  • Mother generates anti-Rh antibodies (IgG) during exposure to an Rh positive baby at
    • delivery
    • amniocentesis
    • abortion
    • ectopic pregnancy
  • During her second pregnancy antibodies cross the placenta and cause hemolysis in the fetus
    • fetal disease depends on how much IgG crosses placenta and ability of fetus to replenish RBC
    • causes fetal anemia leading to
      • ascites and edema
      • high output cardiac failure
      • worst case scenario is hydrops fetalis
  • Rh is a surface protein on RBC that is carried in an autosomal dominant fashion
    • if the mother is Rh negative, but the father is Rh positive, there is a 50% chance that the baby will be Rh positive
Evaluation
  • Identify at-risk pregnancies
    • mother is Rh negative and father is either positive or unknown 
  • Identify fetal anemia
    • analyze amniotic fluid for evidence of hemolysis via bilirubin levels
      • meased as optical density (ΔOD450)
    • perform percutaneous umbilical cord sampling
Treatment

  • Administer RhoGAM (Anti-Rh antigen) if mother Rh negative and father Rh positive
    • within 72 hours of delivery, risk of subsequent sensitization drops from 15% to 2%
    • if given at 28 weeks risk drops to 0.2%
  • Other times to administer RhoGAM
    • amniocentesis
    • external cephalic version 
    • abortion
    • ectopic pregnancy
    • Kleihauer-Betke test measure fetal RBCs in maternal circulation and determine degree of fetal-maternal bleed and consequent dose of RhoGAM to administer


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