Rhesus Disease Flashcards
Define rhesus disease
RBC isoimmunisation occurs when the mother mounts an immune response against antigens on fetal RBCs that enter her circulation. The resulting antibodies then cross the placenta and cause fetal RBC destruction.
What blood groups do the parents need to have for this to occur?
A rhesus positive father and a rhesus negative mother
What is the pathogenesis behind rhesus disease?
- Incompatible antigens introduced result in a primary immune response and stimulate production of maternal antibodies
- Very small amount of fetal-maternal haemorrhage needs to occur
- Primary exposure can also be the result of amniocentesis or CVS
- Rarely any problems in primary exposure but subsequent pregnancies result in large amounts of maternal anti-D antibodies being produced and the risk increases with each gestation
- Cross placenta and affix to fetal RBCs where they become recognised as foreign by fetal immune system and then haemolyse
- Significant haemolysis results in anaemia, hyperbilirubinaemia and production of excessive erythroid tissue in liver, spleen, bone marrow, skin and placenta
- In severe cases multiorgan dysfunction and hypoproteinaemia can develop
How do we identify at risk women?
- If unsensitised, screen at booking and at 28wks
- Maternal blood sampling for fetal DNA if father heterozygote
- Anti-D <10iu/L recheck every 2-4wks
- Anti-D >10iu/L = further investigations
- Anti Kell = USS earlier as levels not helpful
How is severity of fetal anaemia assessed?
- Non-invasive = increased peak velocity in systole in middle cerebral artery (MCA PSV) - highly sensitive before 36wks
- Do fortnightly in at risk pregnancies
- Very severe anaemia (<5g/dL) detectable as hydrops or excess fluid on USS = fetal blood sampling
How do we treat fetal anaemia?
- In utero transfusion - be prepared to deliver if complications
- Deliver if >36wks
What are the steps in managing haemolytic disease of the newborn from an obstetric point of view?
- Identify at risk women
- Assess severity of fetal anaemia
- Treatment of fetal anaemia
List the potentially sensitising events
- Termination of pregnancy (medical or surgical)
- Evacuation of the uterus (medical or surgical)
- Ectopic pregnancy
- Threatened or complete miscarriage after 12wks
- Antepartum haemorrhage
- Invasive prenatal procedures e.g. amniocentesis, CVS, FBS, ECV
- Abdominal injury
- IUD
How can we measure fetal-maternal haemorrhage (FMH)?
- Kleiheuer - HbF in maternal circulation
- Flow cytometry - more accurate, less widely available (suspend cells in stream of fluid and pass them through an electronic detection apparatus)
What is Anti-D and how is it used?
The Anti-D immunoglobulin neutralises and RhD positive antigens that may have entered the mother’s blood during pregnancy
If the antigens have been neutralised, the mother’s blood won’t produce antibodies
What is the sensitising events dose of Anti-D?
- <20wks = 625iu
- >20wks = 1000iu + kleiheuer
What is routine antenatal prophylaxis with anti-D?
- Recommended for all non-sensitised RhD negative women
- 28wks gestation
- One dose regimen (1500iu)
What is postnatal anti-D prophylaxis and when is it given?
- 1250iu within 72hrs of delivery if fetal blood group is Rh positive
- Cord blood - ABO and Rh group, Hb, direct Coombs, bilirubin
- Check FMH (kleiheuer)
Who doesn’t get anti-D?
- Those already sensitised (have antibodies to the D antigen)
- Father of the child is Rh negative
- Definite about not having any more babies
List the risks of anti-D
- Allergic reaction
- Blood product - risk transmission of disease (Irish controversy 1990’s anti-D contaminated with Hep C virus, many women were affected)
