8A) Antenatal Care: Red cell antibodies Flashcards
Incidence of red cell antibodies
1.2% (0.4% clinically significant)
Most common red cell antibody
anti-D
Incidence of anti-D prior to prophylaxis introduction
20% after a first pregnancy
Which antibodies carry greatest risk of fetal anaemia?
anti-D
anti-c
anti-K
Combination of anti-C and anti-E
Survival rates in pregnancies affected by fetal immune anaemia (with treatment)
84% (74% if hydrops, 94% without hydrops)
Management of mum with antibodies detected
(1) Test fetus with cffDNA
(2) Measure titres of antibodies
If significant history of HFDN, or significant titres or ultrasound features of anaemia refer to FMU.
What constitutes significant titres of each antibody?
anti-D: >4 (>15 is severe)
anti-c: >7.5 (>20 is severe)
anti-K: Any titre
Other antibodies: >32 (unless anti-C and anti-E in combination in which case lower threshold)
When would you consider invasive testing to determine fetal antigen status?
If history of severe HFDN or signs of anaemia.
Ultrasound monitoring of fetus at risk
If fetus carries antigen for maternal antibody which is capable of causing fetal anaemia and titres are over the limit - weekly USS to assess MCA peak systolic velocity.
If MCA >1.5MoM or other signs of fetal anaemia (polyhydramnios, skin oedema, cardiomegaly) - refer for treatment.
How often to measure antibody titres?
Anti-D/c/K: 4 weekly until 28 weeks and then 2 weekly until delivery.
Other antibodies: Retest 28/4 unless hx HFDN.
Treatment of HFDN
Fetal transfusion using:
- Group O blood
- Negative for antigen
- Negative for K antigen
- CMV negative
- Irradiated
- Plasma reduced to give HCT 0.70-0.85
Timing of delivery
For antibodies that could cause anaemia but that have been stable throughout pregnancy - 37-38 weeks.
If IUT then time to maximise fetal Hb.
Continuous CTG.
Cord samples for DAT/Hb/bilirubin.
When can cffDNA be used to determine fetal antigen status?
From 16 weeks (20 weeks if anti-K antibodies)
When should blood be crossmatched?
Every week for women with antibodies at high risk of needing transfusion
What is the sensitivity of MCA dopplers for detecting fetal anaemia?
100%