In North America, a standard dose of RhIg is considered to be 1500 IU (300 µg). Note: 1 µg of anti-D = 5 IU.
300 µg of RhIg can suppress immunization to approximately 30 mL of D-positive whole blood (15 mL of packed cells). If gestational age is known to be less than 12 weeks, a 600 IU (120 µg) dose may be sufficient.
Depending on the gestation of the fetus, recommended dosages vary from country to country and within countries. Samples of recommendations that may change over time:
- USA: American College of Obstetricians and Gynecologists (1999, reaffirmed 2007): Antenatal RhIg dose of 300 µg (1500 IU) at 28 weeks and another 300 µg after delivery of a D-positive infant.
- Canada: Society of Obstetricians and Gynaecologists of Canada (2003): Antenatal RhIg dose of 300 µg (1500 IU)at 28 weeks (alternatively, 2 doses of 100–120 µg, one at 28 weeks and one at 34 weeks). After delivery of a D-positive infant, another 300 µg (alternatively, 120 µg IM or IV).
- UK: Royal College of Obstetricians and Gynaecologists (2002): Antenatal RhIg does of 100 µg (500 IU) at both 28 weeks and 34 weeks of gestation, and another 100 µg after delivery of a D-positive infant.
All recommendations require testing to detect larger fetal bleeds, e.g., FMH larger than 30 mL of whole blood (for 300 µg doses) and FMH over 12 mL of rbc for 100 µg doses.