Rh(D) alloimmunisation and anti-D prophylaxis

It is the antenatal booking visit. A 29-year-old G2P1, blood group A RhD-negative, is in front of you. Her first baby was RhD-positive and healthy; she had anti-D then. This time her booking antibody screen is positive for anti-D at a titre of 1:32. The registrar asks you: "Do we just give more anti-D?" No. Anti-D is prevention; once a woman is sensitised it does nothing. The whole game now is detecting fetal anaemia non-invasively and transfusing before hydrops. This topic is the script for both halves — preventing sensitisation, and managing it when prevention has failed.^[2][8]

Overview and definition

Rh(D) alloimmunisation is two diseases separated by a moment of prevention. Untreated, it is haemolytic disease of the fetus and newborn (HDFN) — maternal IgG crosses the placenta, coats fetal RhD-positive red cells, and triggers extravascular haemolysis that can end in hydrops, stillbirth, or kernicterus. Treated with anti-D immunoglobulin, it is a preventable success story of modern obstetrics.^[6]

Three terms the examiner separates for you: ^[2]

• Sensitisation — the asymptomatic event. Maternal B-cells meet fetal RhD antigen and form anti-D. No fetal harm yet, and anti-D given now cannot reverse it.
• Alloimmunisation — the established state. Anti-D is present on the maternal screen. Future pregnancies are at risk.
• HDFN — the fetal and neonatal disease. Maternal IgG haemolyses fetal cells, causing anaemia, hydrops, and neonatal jaundice.^[2]

The distinction matters because anti-D is prevention, not treatment. Once anti-D appears on the screen, you stop giving prophylactic anti-D and start surveillance.^[2][8]

^{[2] [6]}

References14ShowHide

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2. [2]Moise KJ Jr Management of rhesus alloimmunization in pregnancy Obstet Gynecol, 2008.PMID 18591322
3. [3]Moise KJ Jr, Argoti PS Management and prevention of red cell alloimmunization in pregnancy: a systematic review Obstet Gynecol, 2012.PMID 23090532
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6. [6]Practice Bulletin No. 181: Prevention of Rh D Alloimmunization Obstet Gynecol, 2017.PMID 28742673
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11. [11]Pilgrim H, Lloyd-Jones M, Rees A Routine antenatal anti-D prophylaxis for RhD-negative women: a systematic review and economic evaluation Health Technol Assess, 2009.PMID 19210896
12. [12]Saramago P, Yang H, Llewellyn A, et al. High-throughput, non-invasive prenatal testing for fetal Rhesus D genotype to guide antenatal prophylaxis with anti-D immunoglobulin: a cost-effectiveness analysis BJOG, 2018.PMID 29415334
13. [13]Moise KJ Jr, Markham KB, Spinella PC, et al. A Clinical Practice Guideline for the Management of Pregnancy Alloimmunized to Red Blood Cell Antigens JAMA Netw Open, 2025.PMID 41284292
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