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rh_isoimm

Rh isoimmunisation and Anti-D

Introduction

  • all patients who are Rh -ve and are pregnant are at risk of developing Rh iso-immunisation which is the development of permanent maternal antibodies against fetal Rh +ve red blood cell markers. Once this occurs fetal haemolytic anaemia will result causing erythroblastosis fetalis which tends to be worse in magnitude with successive pregnancies and may cause fetal demise.
  • although the rate of iso-immunisation developing in an otherwise uneventful pregnancy is approximately 1-2%, mismanagement of patients who present with increased risk may result in significant medicolegal issues.
  • risk factors for iso-immunisation are any circumstance that may allow fetal red blood cells into maternal circulation such as:
    • confirmed miscarriage (NB. Anti-D is no longer needed for threatened miscarriage in 1st 12 wks)
    • medical procedures such as amniocentesis, chorionic villous sampling, termination of pregnancy, fetal rotation
    • abruption
    • placenta praevia
    • trauma to pregnant abdomen
    • Caesarian section or vaginal delivery (send cord blood as well)

Prevention:

  • administration of an appropriate dose of Anti-D within 72hrs of the risk event commencing
  • NB. mini-dose Anti-D of 250IU commenced in Australia in May 2001 due to shortages of Anti-D, this is sufficient to prevent immunisation by a fetomaternal haemorrhage of 2.5ml of RBC's (ie. 5ml of whole blood) and will cover any event in 1st trimester.

Management of sensitising events in pregnancy:

  • in any Rh -ve patient who has the above risk factors, and are not known to be already iso-immunised (ie. do not already have Rh antibodies), she should be managed as follows:

1st trimester:

  • if no Rh Anti-D has been given within 1-2 weeks (the usual duration of action):
    • check Rh antibody levels:
      • if no antibodies give mini-dose Anti-D 250IU (625IU if multiple pregnancy)
      • if antibodies present:
        • confirm with laboratory that they were from recent Anti-D dose and whether sufficient amount:
          • if insufficient levels from recent Anti-D, consider repeat mini-dose AntiD
        • if maternal antibodies then refer to O&G for follow up and advice

2nd or 3rd trimester:

  • check Rh antibody levels and request Kleihauer test (FBE tube, measures fetal RBC and assists with Anti-D dosing):
    • if no antibodies:
      • give Anti-D 625IU or more if indicated by Kleihauer test
      • NB. patients with BMI > 30 and a feto-maternal haemorrhage > 6mL may require additional iv dose to increase bioavailability and facilitaate more rapid clearance of fetal cells
    • if antibodies present:
      • confirm with laboratory that they were from recent Anti-D dose and whether sufficient amount:
        • if insufficient levels from recent Anti-D, consider repeat Anti-D 625IU
        • if maternal antibodies then refer to O&G and haematologist ASAP for follow up and advice
rh_isoimm.txt · Last modified: 2017/05/19 07:56 by gary1