Monitoring the clearance of fetal RhD-positive red cells in FMH following RhD immunoglobulin administration

Anti-RhD immunoglobulin was administered to RhD-negative women based on est imates of fetal bleed size obtained using a direct immunofluorescence flow cytometric technique employing a FITC-conjugated monoclonal human anti-D (B RAD 3). The effectiveness of the dose administered was assessed by (i) meas uring the fraction of RhD-positive fetal cells in the maternal circulation at d0, and between d2 and d10 post RhD Ig administration, (ii) quantifying the amount of anti-D detectable in maternal plasma following RhD Ig injecti on in the perinatal period and (iii) assessing maternal serum for the prese nce of immune anti-D in follow-up samples taken 3 months to 3 years after d elivery. Fifty-four women were assessed, 29 having fetal bleeds in excess o f 4 mL. Follow-up samples were received from 20/29 mothers after RhD Ig adm inistration; 43-99% and 69-99% of fetal cells had been cleared by d2/3 and d5/6, respectively, in 14/20 mothers, whereas less than 50% had been cleare d in the remaining mothers. Long-term follow-up samples were obtained from eight of the 29 mothers (four with bleeds greater than or equal to 20 mL, t wo with bleeds > 95 mL): none had detectable anti-D in the serum 4 months t o 3 years after delivery despite the persistence of up to 36% fetal RhD-pos itive cells in the maternal circulation six days after delivery.