Blood Group Incompatibility in Pregnancy

1. Blood Group Incompatibility in Pregnancy Max Brinsmead PhD FRANZCOG August 2012

2. RBC isoimmunisation occurs… • Antigenically foreign fetal RBCs enter the maternal circulation • IgG antibodies are formed • Cross back across the placenta • Sensitise fetal RBCs to haemolysis • Causes fetal anaemia • Increases bilirubin in amniotic fluid • And can cause fetal hydrops • Which is high output cardiac failure

3. Disease severity is variable because… • Sensitisation increases with each incompatible pregnancy • Partner’s zygosity is then important • Size of fetomaternal haemorrhage can vary • Maternal reactivity varies • ABO incompatibility may protect from more severe sensitisation e.g. Rhesus D

4. Other causes of RBC isoimmunisation • Incompatible blood transfusion • Sensitisation of Rh Neg baby at birth from an Rh positive mother

5. Types of isoimmunisation • Most are Rhesus D • Rhesus subtypes E, C, e, c • ABO • Kell • Duffey • M • Platelets

6. Monitoring for RBC isoimmunisation • Blood group and RBC antibody screen for all pregnant women • Retest at least once in the 3rd trimester • 98.5% of Rhesus D disease is prevented by event-stimulated administration of Anti-D • 99.9% of Rhesus D disease can be prevented by routine administration Anti-D in the 3rd trimester • Test at 28 weeks and then give anti-D at 28 and 34 weeks

7. Events that require Anti-D for Rh Negative women • Miscarriage, termination of pregnancy or ectopic • Threatened miscarriage (smaller dose, lasts 6w) • CVS or amniocentesis • Antepartum haemorrhage • Abdominal trauma • ECV or attempted ECV • Delivery of an Rh positive baby NB Must be given within 72 hours Requires quantification of fetal blood in maternal circulation and dose adjustment

8. Quantification Methods for Fetal Blood in the Maternal Circulation • Measure passive Anti-D >72 hours after administration • Kleihauer test • Flow cytometry

9. Assessing severity of fetal isoimmunisation • Zygosity studies of the father may be desirable • Titre of antibody in the mother • Quantification of antibody in the mother • Amniocentesis and measure bilirubin • Cordocentesis for Hb and Bilirubin • Now mostly superceded by... • Middle cerebral artery Doppler flow • Blood group fetal blood cells in the maternal circulation

10. Neonatal tests required after fetal isoimmunisation • Collect cord blood for Hb, Bilirubin and direct Coombs test (are the RBCs coated with antibody) • Monitor for neonatal jaundice

11. Treatment of Blood Group Incompatibilities • Neonatal phototherapy • Neonatal exchange transfusion • Pre term delivery (after steroids) • Intrauterine transfusion • To umbilical or hepatic veins • To the peritoneal cavity • Maternal immune suppression

12. ABO Blood Group Incompatibility • Occurs when the mother is blood group O • Natural anti-A & anti-B IgG can cross the placenta • These are weak haemolysins and • There are few sites of attachment to RBCs • Causes neonatal jaundice only • Never an intrauterine problem