8A) Antenatal Care: Red cell antibodies

Question 1

Incidence of red cell antibodies

Answer 1

1.2% (0.4% clinically significant)

Question 2

Most common red cell antibody

Answer 2

anti-D

Question 3

Incidence of anti-D prior to prophylaxis introduction

Answer 3

20% after a first pregnancy

Question 4

Which antibodies carry greatest risk of fetal anaemia?

Answer 4

anti-D
anti-c
anti-K
Combination of anti-C and anti-E

Question 5

Survival rates in pregnancies affected by fetal immune anaemia (with treatment)

Answer 5

84% (74% if hydrops, 94% without hydrops)

Question 6

Management of mum with antibodies detected

Answer 6

(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.

Question 7

What constitutes significant titres of each antibody?

Answer 7

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)

Question 8

When would you consider invasive testing to determine fetal antigen status?

Answer 8

If history of severe HFDN or signs of anaemia.

Question 9

Ultrasound monitoring of fetus at risk

Answer 9

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.

Question 10

How often to measure antibody titres?

Answer 10

Anti-D/c/K: 4 weekly until 28 weeks and then 2 weekly until delivery.
Other antibodies: Retest 28/4 unless hx HFDN.

Question 11

Treatment of HFDN

Answer 11

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

Question 12

Timing of delivery

Answer 12

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.

Question 13

When can cffDNA be used to determine fetal antigen status?

Answer 13

From 16 weeks (20 weeks if anti-K antibodies)

Question 14

When should blood be crossmatched?

Answer 14

Every week for women with antibodies at high risk of needing transfusion

Question 15

What is the sensitivity of MCA dopplers for detecting fetal anaemia?

Answer 15

100%

Question 16

What is the risk of fetal loss following a fetal blood sample?

Answer 16

1-3%

Question 17

What is the shelf life for blood for fetal transfusion compared to neonatal transfusion?

Answer 17

Fetal transfusion has shelf life of 24 hours (due to irradiation).
Neonatal transfusion has shelf life of 5 days.