Postpartum anti-D: can we safely reduce the dose?

To assess the potential for dose-reduction of prophylactic anti-D postpartum.

Retrospective audit of fetomaternal haemorrhage (FMH) quantitation by flow cytometry.

5148 consecutive Rhesus D-negative women aged 15-45 years who had FMH estimation by flow cytometry at a central laboratory in Western Australia in the 65 months between 1 August 1999 and 31 January 2005.

Quantitation of FMH volume for adequate prophylactic anti-D administration in a timely fashion.

90.4% (4651/5148) of the women had an FMH volume of 1.0 mL or less of Rh D-positive red cells, and 98.5% (5072/5148) had a volume of less than 2.5 mL. Only 0.4% of cases had an FMH volume of 6.0 mL or greater (range, 6.0-92.4 mL).

This large retrospective audit shows that a currently available dose of 250 IU (50 mg) of anti-D would have been sufficient for 98.5% of the 5148 Rh D-negative women. On the basis of this evidence, a reduction in the recommended routine postpartum dose of anti-D from 625 IU to 250 IU when flow cytometric quantitation for FMH is available should be considered. Adopting such a strategy would ensure the ongoing provision of a valuable human blood product currently in limited supply.