Rh Hemolytic Disease of the Newborn

Snapshot

• A 32-year-old G1P0 woman presents to the emergency room with contractions. She was found to be Rh-negative and her husband’s Rh status is unknown. Fetal ultrasound shows no signs of edema or ascites. After the Kleihauer-Betke test, she is given the appropriate dose of Rh IgG.

Introduction

• Overview
  • Rh hemolytic disease of the newborn is caused by Rh incompatibility
  • maternal anti-Rh IgG antibodies cross the placenta and destroy fetal Rh-positive red blood cells
• Epidemiology
  • incidence
    • 15% of the population is Rh-negative
  • risk factors
    • history of prior blood transfusion
    • previous pregnancy
    • mother is Rh-negative, and father is Rh-positive or unknown
    • prior administration of Rh IgG (RhoGam)
    • history of invasive obstetric procedures
• Pathogenesis
  • mechanism    
    • Rh factor is a red blood cell antigen
    • when an Rh-negative mother is pregnant with an Rh-positive fetus, the mother is exposed to Rh-positive red blood cells and leads to maternal antibody production (IgG) against the foreign Rh antigen
    • as IgG can cross the placenta, subsequent pregnancy with Rh-positive fetus will result in fetal alloimmune-induced hemolytic anemia
    • development of antibody depends on volume of transplacental crossover of red blood cells, concurrent presence of ABO incompatibility, and extent of maternal immune response
• breakdown of red blood cells causes elevation of bilirubin

Presentation

• Symptoms
  • hemolytic anemia
• Physical exam
  • inspection
    • jaundice
• pallor

Imaging

• Fetal ultrasound
  • indication
    • suspected Rh incompatibility
  • findings
• fetal ascites and edema

Studies

• Serum labs
  • hyperbilirubinemia
  • low hematocrit
  • elevated reticulocyte count
  • positive direct Coombs test in fetus; positive indirect Coombs test in the mother 
• Rosette test
  • initial test to test for fetal-maternal hemorrhage
• Kleihauer-Betke test
• measures fetal red blood cells in utero in maternal circulation to determine dose of RhoGAM

Differential

• ABO incompatibility
  • key distinguishing factor
• typically less severe

Treatment

• Medical
  • maternal anti-D immune globulin (Rh IgG or RhoGAM) administration
    • indication
      • if mother is Rh-negative and has not been sensitized previously, given at 28^th week of pregnancy, if possible, and 72 hours after birth
      • external cephalic version
      • amniocentsis
      • ectopic pregnancy
      • any suspected / known exposure of Rh-positive blood 
  • exchange transfusion
    • indications
      • erythroblastosis fetalis
      • hydrops fetalis
• kernictus

Complications

• Kernicterus secondary to hyperbilirubinemia
  • loss of Moro reflex
  • posturing
  • poor feeding
  • seizures
• Erythroblastosis fetalis 
  • most severely, can manifest as hydrops fetalis with high output cardiac failure, edema, and death
  • indication for immediate delivery and exchange transfusion