Routine antenatal anti-D prophylaxis--is the protection adequate?

Prophylactic anti-D given during pregnancy can be detected in current indirect antiglobulin tests (IAT). Using this to measure the persistence of prophylactic anti-D, this study set out to determine whether there is an association between anti-D detectable at delivery and the RhD status of the foetus and/or the duration of the pregnancy post the standard 28 week dose of routine antenatal anti-D prophylaxis (RAADP). The study also investigated the detection rates of anti-D at delivery when given in a two dose regime or a one dose regime.

All IAT screening was undertaken using fully automated Diamed gel technology. The results from 407 women were included in the two dose regime study, and 157 in the one dose regime study.

160/407 (39%) women receiving one dose of prophylactic anti-D had no detectable anti-D at delivery. 123/157 (78%) women on the one dose regime had no detectable anti-D at delivery. No association was found between detectable anti-D at delivery and the RhD status of the infant in either study arm. A strong association was found between detectable anti-D Ig at delivery and the duration of the pregnancy post the 28 week dose in each study arm.

Our data show that neither the two dose nor the one dose regime appear to provide adequate cover at delivery for a large percentage of pregnant women. This appears to be associated with the duration of the pregnancy past the 28 week dose but not associated with the RhD status of the foetus.