Rh(D) alloimmunisation and anti-D prophylaxis — structured SAQ (15 marks)

(a) Routine antenatal anti-D prophylaxis (3 marks)

One mark per element; full marks need drug, dose, route and timing. ^[4]

• Drug and product: Rh(D) immunoglobulin (anti-D), intramuscular.^[4]
• Dose and timing: two doses of 625 IU, one at 28 weeks and one at 34 weeks, to the RhD-negative woman without preformed anti-D.^[4]
• Confirm negative antibody screen before the first dose (a positive screen means sensitisation has already occurred and prophylactic anti-D is pointless).^[2]

(b) Antepartum haemorrhage at 26 weeks — sensitising-event management (3 marks)

One mark per point. ^[4]

• Give anti-D for the event: because the bleed is over 12 weeks, the dose is 625 IU IM, given as soon as possible (within 72 hours).^[4]
• Quantify the fetomaternal haemorrhage with a Kleihauer-Betke test (or flow cytometry); the standard 625 IU covers up to 6 mL of fetal red cells.^[4]
• Top up for the excess: the Kleihauer estimates 8 mL, so 2 mL exceeds the 6 mL cover — give additional anti-D at 100 IU per 1 mL of fetal red cells over 6 mL, so 200 IU additional. Do not delay the initial 625 IU while awaiting the result.^[4]

(c) Postpartum management (3 marks)

One mark per point. ^[4]

• Confirm the infant is RhD-positive on cord blood (blood group and direct antiglobulin test) before giving postpartum anti-D.^[4]
• Give 625 IU IM within 72 hours, without waiting for the Kleihauer result.^[4]
• Quantify the fetomaternal haemorrhage (Kleihauer or flow cytometry); give additional anti-D at 100 IU per mL of fetal red cells over 6 mL if the bleed is larger than the standard cover.^[4]

(d) Previously-affected alloimmunised pregnancy (6 marks)

The high-value part. Marks for the surveillance pathway, the key thresholds, and the management triggers. ^[2][3]

• Anti-D is now useless — she is already sensitised; do not give prophylactic anti-D.^[2]
• Titres are non-predictive in a previously affected pregnancy. Do NOT monitor with serial titres; go straight to serial middle cerebral artery peak systolic velocity (MCA-PSV) Doppler from 16 to 18 weeks.^[2]
• The action threshold: when MCA-PSV rises above 1.5 multiples of the median for gestation, perform fetal blood sampling with an intrauterine transfusion (IUT) ready, unless gestation makes delivery safer.^[3]
• Refer to a fetal medicine centre with intrauterine transfusion capability.^[3]
• IUT technique (one mark): intravascular via cordocentesis into the umbilical vein at the placental insertion; O-negative, CMV-negative, irradiated, crossmatch-compatible packed cells; repeat guided by predicted haemoglobin decline (about 1 g/dL per week) and serial MCA-PSV.^[2]
• Outcome and neonatal plan (one mark): perinatal survival after IUT exceeds 90 percent; plan neonatal cord blood group, direct antiglobulin test, bilirubin and haemoglobin, with phototherapy and top-up readiness; counsel on recurrence and escalation next time.^[2]