Evaluation of 6 years of fetal RHD screening in Ireland: From implementation to practice

BACKGROUND AND OBJECTIVES: The discovery of circulating fetal DNA in maternal plasma enabled non-invasive prenatal testing (NIPT) for targeted anti-D prophylaxis. In 2019, Ireland implemented an in-house test to guide this care. Here, we report 6 years of service. MATERIALS AND METHODS: Cell-free fetal DNA (cffDNA) was extracted from 1000-μL plasma from pregnant RhD negative women at gestation age (GA) > 11 weeks. Samples were tested in triplicate for RHD by quantitative PCR using a multiplex assay of RHD exons 7 and 10. RESULTS: Of the 20,099 samples tested, 58.2% were predicted RhD positive and 36.9% were predicted RhD negative. Discrepancies were seen in 52 cases: 7 (0.03%) were predicted RhD negative but cord RhD positive and 45 (0.2%) were predicted RhD positive but cord RhD negative. CONCLUSION: This test has ensured that over 7400 women have avoided unnecessary anti-D prophylaxis. There were few discrepant results, with false negatives posing a greater clinical risk due to withheld anti-D, increasing immunization risk. Three were linked to pre-analytical errors prompting procedural changes. Due to the success of fetal RHD screening, cord blood testing has been discontinued in some countries; a practice which could be reviewed in Ireland.