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Rhesus Isoimmunisation
 

Rhesus Isoimmunisation

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SALSO Series - Rhesus Isoimmunisation

SALSO Series - Rhesus Isoimmunisation

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    Rhesus Isoimmunisation Rhesus Isoimmunisation Presentation Transcript

    • Rhesus isoimmunization
    • Basic – Blood group & Rhesus
      • 2 most important blood group systems
        • ABO group
        • Rhesus group
    • ABO blood group No No Yes Yes AB Yes Yes No No O No Yes Yes No B Yes No No Yes A Anti-B Anti-A Antigen B Antigen A ABO blood type
    • Rhesus blood group No No Rhesus –ve No Yes Rhesus +ve D-antibody D-Antigen D D D D D D D D D D D D D D D D
    • Epidemiology <1% Asians 5-10% African-Americans (Blacks) 15% Caucasian Racial variation in incidence of Rh negative
    • Basic - isoimmunization
      • Occurs when:
        • Mother is Rh –ve
        • Baby is Rh +ve
        • Fetomaternal haemorrhage occurs
          • Antepartum haemorrhage
          • Falls or closed abdominal trauma
          • Intrauterine death
          • External cephalic version
          • Invasive prenatal diagnosis (e.g. amniocentesis, chorionic villus sampling)
    • Basic - Isoimmunization Fetomaternal haemorrhage – fetal RBC enter maternal circulation Formation of antibodies to D antigen (anti-D) - sensitization Later in pregnancy or next pregnancy, anti-D crosses placenta Anti-D attacks fetal Rh +ve RBCs and are destroyed by the immune system – haemolytic anaemia
    • Importance
      • Rh –ve mothers are at risk of developing Rh isoimmunization if the fetus is Rh +ve
      • If a mother has been sensitized before, there is a risk of the Rhesus +ve fetus developing hemolytic anaemia and in severe cases, hydrops fetalis
    • How to prevent isoimmunization?
      • Prevent mother from forming Anti-D antibodies by giving RhoGAM (Anti-D antibodies)
    • Why RhoGAM?
      • Prophylactic anti-D Ig has resulted in a substantial fall in perinatal mortality and morbidity from rhesus D disease
    • Rhesus +ve men
      • 55% are heterozygous (Dd) – 50% chance of Rh-positive fetus
      • 45% are homozygous (DD) – 100% chance of Rh-positive fetus
    • Risk of isoimmunisation 0.1-0.2% Postpartum + antepartum RhoGAM 1-2% Postpartum RhoGAM 8% Subsequent pregnancy - untreated 16% 1 st Rh-incompatible pregnancy – untreated Risk of isoimmunisation
    • Indications for RhoGAM
      • Miscarriage
        • All therapeutic termination – irregardless of gestational age or methods (medical or surgical)
        • All surgical evacuation (ERPOC @ S&C)
        • Threatened miscarriage >12 weeks
        • Threatened miscarriage <12 weeks with
          • Heavy or repeated bleeding
          • Abdominal pain
    • Indications for RhoGAM
      • Ectopic pregnancy
      • Conditions a/w fetomaternal haemorrhage
        • Antepartum haemorrhage
        • Falls or closed abdominal trauma
        • Intrauterine death
        • External cephalic version
        • Invasive prenatal diagnosis (e.g. amniocentesis, chorionic villus sampling)
    • Not indicated
      • Complete spontaneous miscarriage <12 weeks
      • Threatened miscarriage <12 weeks POA (with cessation of bleeding before 12 weeks POA)
      • Reason – unlikely to cause significant FMH
    • RhoGAM – Dosage & administration
      • Dose
        • Before 20 weeks : 250 IU
        • After 20 weeks : 500 IU
        • Postpartum : At least 500 IU
        • Note : Kleihauer test should be performed when anti-D Ig is given after 20 weeks
          • To estimate volume of FMH
          • Additional anti-D Ig if FMH > 4 mL fetal cells (125 IU prevents immunization with 1 ml fetal cells)
    • RhoGAM – Dosage & administration
      • Route : Deep IM injection – preferably deltoid muscle
      • Timing : Postpartum – <72 hours
        • May still be given if presented later (10-14 days)
    • Clinical setting
      • Refer to hospital as early as possible if:
        • Rhesus negative pregnant mother (either 1 st time detected or known rh –ve previously)
        • Known rhesus negative with risk of FMH (e.g. threatened miscarriage, APH, fall, abdominal trauma, etc.)
    • Clinical setting
      • Screened for maternal anti-D (sensitization) – Indirect Coomb’s test
        • At booking
        • Just before 28 weeks
      • If not sensitized, RhoGAM is administered:
        • 500 IU at 28 & 34 weeks
        • 1,500 IU at 28 weeks only
        • No need to check Indirect Coomb’s test after Rhogam as it may be positive due to Rhogam itself
        • Postnatal RhoGAM is still given
    • Clinical setting
      • If sensitized, close monitoring of:
        • Fetus
        • Anti-D level
        • Timing and mode of delivery depending of status of fetus
    • Oxford Rhesus Therapy Unit mx guidelines 34+ Yes 2 > 16.0 34-38 Yes 2 10.1-16.0 36-38 No 2 4.1-10.0 Term No 2 0.5 - 4.0 Term No 4 < 0.5 Gestation at which delivery advised Invasive testing Repeat antibody quantitation (weeks) Anti-D quantitation (IU/ml)
    • Non-invasive fetal monitoring
      • Ultrasound – features of hydrops
        • Ascites
        • Pleural effusion
        • Soft tissue/scalp edema
        • Cardiomegaly
        • Hepatomegaly
      • Doppler – middle cerebral artery
      • FKC
      • CTG
    • Thank you