At delivery, women in the two-dose regimen had higher levels of anti-D than women who had received one dose
Australia’s recommended two-dose routine antenatal anti-D prophylaxis (RAADP) schedule offers better protection against Rhesus D (RhD) sensitisation than the one-dose regimen used in other countries, new research shows.
A randomised controlled trial, published in the latest issue of the Medical Journal of Australia, compared the level of circulating Rh(D) immunoglobulin at delivery for women given either the Australian regimen of two doses of anti-D prophylaxis or a single-dose regimen.
At delivery, women in the two-dose regimen had higher levels of anti-D than women who had received one dose, researchers said.
“Prior to our trial, the Australian regimen had never been compared head-to-head with a single dose regimen, such as that currently recommended in some other countries,” Dr Scott White, an Associate Professor in the Faculty of Health and Medical Sciences at the University of Western Australia, and co-author of the study, told The Medical Republic. “There was clear evidence that both regimens are effective in reducing Rh(D) sensitisation, but it was not clear if one was better than the other.”
“Our results suggest that the two-dose regimen should continue to be recommended as it is better able than a single-dose regimen to maintain detectable levels of anti-D in the maternal circulation until birth. This provides better protection against antenatal Rh(D) sensitisation in Rh(D)-negative women and reduces the risk of complications in future pregnancies,” he said.
Once regarded as a mysterious disease, Rh(D) disease (also referred to as Rhesus disease, or haemolytic disease of the foetus and newborn (HDFN)) has a long history. Scholars of history have surmised it may have been the reason for the obstetric problems experienced by Catherine of Aragon, first wife of England’s King Henry VIII.
Since it was first introduced in Australia in the 1960s, anti-D prophylaxis has significantly reduced the incidence of Rh(D) disease. RAADP is now recommended for all pregnant women who are Rh(D) negative and non-sensitised.
“Our study suggests that the current recommendation of two 625IU doses of anti-D at 28 and 34 weeks should be maintained for all Rh(D)-negative women not known to be carrying Rh(D)-negative foetuses,” Dr White said.
Around 17% of pregnant women in Australia need anti-D prophylaxis, which comes from the plasma of just 200 donors with the right antibodies.
Dr White said new technologies that could determine the fetal blood group from a maternal blood sample would soon help clinicians ensure the limited anti-D plasma available was used appropriately.
“Using this allows us to target the use of antenatal anti-D only to those women known to be carrying a Rh(D)-positive foetus and avoiding using it in women with Rh(D)-negative foetuses who are not at risk. This is not currently routinely available in all of Australia, but is likely to become so soon.”
Compliance was low in both the single-dose and two-dose groups studied, with 38% of women in the single dose group and half of those in the two-dose group not given the appropriate dose of anti-D at the appropriate time for their assigned regimen. Those in the single-dose group were more likely to receive an incorrect dose, while those in the two-dose group were more likely to miss a dose or have a late dose.
Dr White argued this wasn’t ideal, and should be addressed.
“Compliance could be improved by employing robust systems of reminders to clinicians and women that anti-D is due to be given and ensuring that women do not have to go to additional steps to access it,” he said.
“For example, having anti-D available in the antenatal clinic or obstetrician’s office reduces the steps required to access it and therefore the chance for errors of omission. Ensuring that women understand the rationale for anti-D prophylaxis and the safety of the product will reduce the number of women who decline recommended prophylaxis.”
