Rh Sensitization

Aka: Rh Sensitization, Rh Isoimmunization, Rh Alloimmunization, Rhesus Isoimmunization Affecting Pregnancy

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II. Pathophysiology

  1. Maternal Antibody Formation to fetal Rh
    1. IgM (Agglutinates in Normal Saline) forms in 7 days
      1. Does not cross placenta
    2. IgG (Agglutinates in Albumin) forms in 21 days
      1. Crosses placenta easily
  2. Results in Hemolytic Disease of the Newborn
    1. Neonatal Hemolytic Anemia
    2. Fetal hydrops

III. Indications: RhoGAM (xD) Administration to Rh Negative Mother

  1. Standard Timing
    1. Week 28 gestation
    2. Postpartum (under 3 days postpartum if baby Rh+)
  2. Additional Indications
    1. Placenta Separation
    2. Labor Third Stage
    3. Termination or Spontaneous Abortion after 6 weeks
      1. Rh Isoimmunization Risk 1.5 to 2%
      2. Risk increases to 4 to 5% with Dilation and Curettage
    4. Antepartum bleed
    5. Abruptio Placenta
    6. Abdominal Trauma
  3. Procedures (Give RhoGAM within 72 hours of procedure)
    1. Amniocentesis or Cordocentesis
    2. Chorionic Villus Sampling
    3. External version

IV. Dosing

  1. Standard RhoGAM Dosing
    1. Before 12 weeks gestation: RhoGAM 50 mcg IM
      1. RhoGAM 50 mcg IM has limited availability
      2. Now RhoGAM 300 mcg IM is given at this time
    2. After 12 weeks gestation: RhoGAM 300 mcg IM
  2. First Trimester Bleeding or Late Pregnancy Bleeding
    1. RhoGAM dose based on Kleihauer-Betke Test

V. Labs: Rh Negative mother

  1. Consider checking Rh type of father if paternity sure
  2. Indirect Coombs Test for Rh Antibodies
    1. Identify specific antibodies
    2. Titer may be weakly positive (1:4) from prior RhoGAM
    3. Titer > 1:8 dilution requires evaluation
    4. Follow Antibody titer monthly
  3. At Delivery: Test fetal blood
    1. Maternal blood Sheep Rosette if fetus Rh Positive
    2. Sheep Rosette test results
      1. Negative: Give 300 mcg RhoGAM
      2. Positive: Kleihauer Bettke based Rh vial numbers

VI. Imaging

  1. Fetal Ultrasound: signs of Fetal hydrops
    1. Fetal Ascites
    2. Scalp edema
  2. Amniocentesis (replaced by MCA-PSV in most cases)
    1. Obtain every 1-3 weeks when fetus > 26 weeks
    2. Follow Bilirubin level in amniotic fluid
    3. Liley Curve directs management per Gestational age
      1. Amniotic Bilirubin level >0.3 at 27 weeks gestation
      2. Amniotic Bilirubin level >0.2 at 31 weeks gestation
      3. Amniotic Bilirubin level >0.1 at 36 weeks gestation
  3. Middle Cerebral Artery Peak systolic velocity (MCA-PSV)
    1. Best noninvasive marker for fetal Hemoglobin level
    2. Depends on accurate gestation age
    3. Reliable from 18-35 weeks
    4. Interpreted on curve to determine severity
  4. Genotyping
    1. Determines if fetus at risk of Rh Sensitization
    2. Previously required Amniocentesis
    3. Now cell free fetal DNA detected in maternal serum

VII. Management (Based on severity evaluation above)

  1. Neonatology Consultation
  2. Corticosteroids may be indicated
  3. Phenobarbital may be indicated
  4. Consider reducing maternal antibodies <18 weeks
    1. Plasmapheresis of maternal serum or
    2. Intravenous IgG
  5. Consider early delivery (32-35 weeks)
    1. Do not wait for Fetal hydrops
  6. Intrauterine transfusion via Ultrasound guidance
    1. Indicated for severe cases based on testing above
      1. Intravascular fetal transfusion via Umbilicus
      2. Intraperitoneal transfusion
        1. Poorly absorbed in Fetal hydrops

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