Terminating Routine Cord Blood RhD Typing of the Newborns to Guide Postnatal Anti-D Immunoglobulin Prophylaxis Based on the Results of Fetal RHD Genotyping

Abstract

<b><i>Introduction:</i></b> Targeted routine antenatal prophylaxis with anti-D immunoglobulin (Ig) only to RhD-negative pregnant women who carry RhD-positive fetuses (determined by fetal <i>RHD</i> genotyping) has reduced D-alloimmunization significantly when administered in addition to postnatal prophylaxis. Achieving high analysis sensitivity and few false-negative fetal <i>RHD</i> results will make RhD typing of the newborn redundant. Postnatal prophylaxis can then be given based on the result of fetal <i>RHD</i> genotyping. Terminating routine RhD typing of the newborns in cord blood will streamline maternity care. Accordingly, we compared the results of fetal <i>RHD</i> genotyping with RhD typing of the newborns. <b><i>Methods:</i></b> Fetal <i>RHD</i> genotyping was performed, and antenatal anti-D Ig was administered at gestational week 24 and 28, respectively. Data for 2017–2020 are reported. <b><i>Results:</i></b> Ten laboratories reported 18,536 fetal <i>RHD</i> genotypings, and 16,378 RhD typing results of newborns. We found 46 false-positive (0.28%) and seven false-negative (0.04%) results. Sensitivity of the assays was 99.93%, while specificity was 99.24%. <b><i>Conclusion:</i></b> Few false-negative results support the good analysis quality of fetal <i>RHD</i> genotyping. Routine cord blood RhD typing will therefore be discontinued nationwide and postnatal anti-D Ig will now be given based on the result of fetal <i>RHD</i> genotyping.