8A) Antenatal Care: Red cell antibodies Flashcards

1
Q

Incidence of red cell antibodies

A

1.2% (0.4% clinically significant)

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2
Q

Most common red cell antibody

A

anti-D

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3
Q

Incidence of anti-D prior to prophylaxis introduction

A

20% after a first pregnancy

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4
Q

Which antibodies carry greatest risk of fetal anaemia?

A

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

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5
Q

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

A

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

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6
Q

Management of mum with antibodies detected

A

(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.

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7
Q

What constitutes significant titres of each antibody?

A

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)

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8
Q

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

A

If history of severe HFDN or signs of anaemia.

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9
Q

Ultrasound monitoring of fetus at risk

A

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.

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10
Q

How often to measure antibody titres?

A

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

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11
Q

Treatment of HFDN

A

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
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12
Q

Timing of delivery

A

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.

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13
Q

When can cffDNA be used to determine fetal antigen status?

A

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

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14
Q

When should blood be crossmatched?

A

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

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15
Q

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

A

100%

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16
Q

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

A

1-3%

17
Q

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

A

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