Altered strategy of prophylactic anti‐D administration in pregnancy to cover term and post‐term – a pilot study

Abstract

Background and objective Routine antenatal anti-D prophylaxis (RAADP) to RhD-negative women is most often administered in gestational age (GA) 28-30 weeks with the next anti-D dose administered postpartum. The aim of this study was to analyse the proportion of RhD-negative women where RAADP is not detectable at term and in a pilot study to investigate whether RAADP administered in GA 28 and 38 results in detectable levels at term, post-term and postdelivery. Materials and methodsIn a retrospective analysis, 4280 RhD-negative women carrying an RHD positive fetus were included and the proportion with a negative antibody screen at delivery was determined. In the second part, 39 pregnancies were included prospectively, a second dose of RAADP was administered in GA 38 weeks, and anti-D was quantified before the second dose and then weekly for 5 weeks. ResultsIn the retrospective analysis, 20Á5% (856/4280) with RAADP administered in GA 28 were negative in routine antibody screening at delivery. In the small prospective study, 18% (7/39) had a negative antibody screen and 26% (10/39) had levels below 0Á005 IU/ml, in the quantification assay, in GA 38. Anti-D prophylaxis administered in GA 38 showed detectable levels of anti-D up to 30 days post-delivery, with concentration at delivery 0Á060 -0Á034 IU/ml (mean -SD). ConclusionApproximately 20% of the RhD-negative women show non-detectable levels of anti-D at term. A second dose of RAADP at GA 38 results in stable concentrations of anti-D at term, post-term and post-delivery, but with large interindividual variation.

Following targeted routine antenatal anti‐D prophylaxis, almost half of the pregnant women had undetectable anti‐D prophylaxis at delivery

“…The lack of detectable anti‐D Ig at delivery and its implications for the prevention of RhD immunization during the last weeks of pregnancy is a common concern and indicates that the prophylaxis does not last long enough to cover the whole third trimester, especially the critical last couple of weeks when the risk of FMH is highest 7–9,15 . It does not necessarily mean that the RhD‐negative pregnant woman is unprotected and prone to RhD alloimmunization, but it does predict clearance due to the half‐life of anti‐D Ig and it may imply a silent FMH consuming anti‐D Ig 16 .…”

“…The lack of detectable anti-D Ig at delivery and its implications for the prevention of RhD immunization during the last weeks of pregnancy is a common concern and indicates that the prophylaxis does not last long enough to cover the whole third trimester, especially the critical last couple of weeks when the risk of FMH is highest. [7][8][9]15 It does not necessarily mean that the RhD-negative pregnant woman is unprotected and prone to RhD alloimmunization, but it does predict clearance due to the half-life of anti-D Ig and it may imply a silent FMH consuming anti-D Ig. 16 The current Note: Chi-squared tests were used to investigate the association between antibody screens at delivery performed at both hospitals, in addition to the association between detectable anti-D and variables such as time interval between RAADP and delivery.…”

“… 7 , 8 However, Wikman et al found that only 20.5% ( n = 4280) of women who received 1250 IU anti‐D Ig at GW 28 had negative antibody screens at delivery. 9 …”

“…[4][5][6] The proportions of nondetectable anti-D at delivery after RAADP at GW 28 are reported to vary from 20.5 to 78%. [7][8][9] The aim of this study was to assess the proportions of nondetectable anti-D in the Norwegian setting when targeted RAADP was given at about GW 28. Furthermore, the presumable impact of dose and timing of prophylaxis administration on non-detectable anti-D Ig at delivery is investigated and discussed to seek potential optimization of the RAADP program.…”

“… 4 , 5 , 6 The proportions of non‐detectable anti‐D at delivery after RAADP at GW 28 are reported to vary from 20.5 to 78%. 7 , 8 , 9 …”