Alloimmunisation (HDFM and FNAIT)

Question 1

CRITO: HDFN

Answer 1

Condition: severe anaemia and thrombocytopaenia due to maternal antibodies against red cells crossing the placenta and attacking fetal red cells.

Maternal risks: transfusion delay.

Fetal risks: anaemia, hydrops, stillbirth, transfusions, preterm birth.

Neonatal risks: NND, anaemia, transfusions, hyperbilirubinaemia and jaundice, kernicterus, SNHL, cholestasis.

Investigations:

• Paternal genotype and/or cell-free fetal DNA (NIPT)
• Monthly titres until 28 weeks.
• 2 weekly titres until delivery.
• Weekly MCA-PSV (>1.5 MoM) + USS for hydrops when titres reach critical level.
• CVS/amnio only if other indication other than fetal genotyping.

Treatment:

• Refer to MFM if anti-K positive; anti-D >4 IU/mL or >=1:16; anti-c >7 IU/mL or >=1:16; OR evidence of anaemia.
• Cordocentesis to confirm fetal anaemia AND perform in-utero blood transfusion

Ongoing management:

• Weekly maternal X-match if at increased risk of bleeding.
• Aim delivery 37-38 weeks unless IUT required then depends on timing of last IUT and rate of drop of fetal Hb.
• Cord bloods at delivery: ABO and RhD typing; DAT; Hb; bilirubin.
• Paed review

Question 2

CRITO: FNAIT

Answer 2

Condition: maternal and paternal platelet type incompatibility leading to development of maternal platelet antibodies that pass through the placenta and destroy fetal platelets leading to thrombocytopaenia.

Risks: fetal and neonatal intracerebral haemorrhage and death. High rate of recurrence 80% next pregnancy.

Investigations:

• Maternal platelet specific alloantibodies.
• Platelet typing and compatibility of mother and father; heterozygous father means fetus at risk.
• Invasive prenatal testing to genotype fetus.
• USS for antenatal ICH +/- MRI

Treatment:

• Refer to MFM
• IVIG from 16 weeks 1g/kg (high risk) or from 28 weeks 0.5g/kg (low risk)
• Offer TOP if antenatal ICH

Ongoing management:

• Antenatal ICH: CS @ 34/40
• Sibling with ICH: CS @ 36/40
• Sibling without ICH: IOL @ 37/40; avoid FSE, FBS, instrumentals.
• Urgent cord blood Plt count +/- Plt transfusion
• Neonatal head USS