Australian Anti-D Prophylaxis Guidelines for Rh-Negative Pregnant Women
Standard Prophylaxis Protocol
All RhD-negative pregnant women should receive anti-D immunoglobulin at 28 weeks gestation and within 72 hours after delivery of an RhD-positive infant, using either a single-dose or two-dose regimen. 1
Antenatal Dosing Options
- Single-dose regimen: 300 μg (1500 IU) at 28 weeks gestation 2
- Two-dose regimen: 100-120 μg at 28 weeks AND 34 weeks gestation (120 μg being the lowest currently available dose in Australia) 2
- Both regimens reduce alloimmunization rates from approximately 1.8% to 0.1-0.2% 1
Postpartum Administration
- Dose: 300 μg IM or IV within 72 hours of delivery if infant is RhD-positive 2
- Alternative: 120 μg IM or IV may be used, with testing for fetomaternal hemorrhage (FMH) >6 mL of fetal red blood cells 2
- Late administration: If the 72-hour window is missed, administer as soon as recognized up to 28 days post-delivery, as delayed administration still provides some benefit 1
Potentially Sensitizing Events Requiring Anti-D
First Trimester (<12 weeks)
- Spontaneous or induced abortion: Minimum 120 μg (50 μg acceptable if available, though 120 μg is the lowest dose currently available in Australia) 1, 2
- Ectopic pregnancy: Minimum 120 μg before 12 weeks 2
- Threatened abortion with heavy bleeding or abdominal pain: Administer anti-D, as 48% of threatened abortions involve fetomaternal hemorrhage 1
- Molar pregnancy: Give anti-D unless complete mole is confirmed (withhold if certain of complete mole) 2
Critical caveat: Fetal RBCs display D-antigens from as early as 6 weeks gestation, making sensitization physiologically possible even in very early pregnancy. 3 Australian audit data shows only 78% of women receive anti-D when recommended for potentially sensitizing events, indicating significant room for practice improvement. 4
After 12 Weeks Gestation
- Miscarriage or abortion: 300 μg 2
- Ectopic pregnancy: 300 μg 2
- Amniocentesis: 300 μg 2
- Chorionic villus sampling: 300 μg 2
- Cordocentesis: 300 μg 2
- External cephalic version: 300 μg with FMH quantification 2
High-Risk Events Requiring FMH Quantification
For events with substantial placental trauma risk, administer 300 μg anti-D immediately AND perform quantitative FMH testing: 2
- Placental abruption
- Blunt abdominal trauma (28% of pregnant patients with minor trauma have FMH) 1
- Placenta previa with bleeding
- Cordocentesis
Additional dosing: If FMH exceeds 15 mL of fetal red blood cells (30 mL fetal blood), give additional 10 μg anti-D per 0.5 mL of fetal red blood cells. 2 Australian data shows poor compliance with supplemental dosing guidelines, with only 11.5% of cases receiving appropriate additional doses. 5
Screening and Testing Requirements
Initial and Follow-up Testing
- First prenatal visit: Blood type and antibody screen (indirect antiglobulin test) for ALL pregnant women 2
- 28 weeks gestation: Repeat antibody screen 2
- Paternal testing: When paternity is certain, offer RhD testing of the father to eliminate unnecessary anti-D administration 2
Special Populations
- Women with "weak D" (Du-positive): Do NOT give anti-D 2
- Cell-free fetal DNA testing: Can determine fetal RHD status with 97.2% sensitivity and 96.8% specificity, or >99% accuracy after 11 weeks gestation, allowing targeted prophylaxis 1
Route of Administration
Both intramuscular and intravenous routes are equally effective. 6 The choice depends on available preparations, dose requirements, and patient preference. Mean anti-D IgG concentrations differ between routes only up to seven days post-administration, but are equivalent from two to three weeks onward. 6
Critical Pitfalls to Avoid
- Do not withhold anti-D based on early gestational age alone: Fetal RBCs with D-antigen are present from 6 weeks onward, and fetomaternal hemorrhage occurs in 7% of first trimester pregnancies 3
- Do not assume minimal bleeding eliminates risk: Bleeding severity does not reliably predict hemorrhage volume, and as little as 0.03-0.1 mL of fetal blood can trigger alloimmunization 3
- Do not skip the 28-week dose: Australian audit data shows only 76% of eligible women receive anti-D at the appropriate time and dose 4
- Do not forget consent documentation: Only 62% of Australian cases had documented consent, which is legally required 4
- Do not skip FMH quantification after high-risk events: Australian data shows a 4% alloimmunization rate following large-volume FMH despite prophylaxis, partly due to inadequate supplemental dosing 5
Effectiveness Data
- Postpartum anti-D alone: Reduces alloimmunization from 13-17% to 1-2% 1
- Adding antenatal dose at 28 weeks: Further reduces alloimmunization from 1.8% to 0.1-0.2% 1
- Most sensitization occurs at delivery: Approximately 90% of fetomaternal hemorrhage and alloimmunization events occur during delivery itself 3, 7