Cell-Free DNA Analysis for the Determination of Fetal Red Blood Cell Antigen Genotype in Individuals With Alloimmunized Pregnancies

OBJECTIVE: To evaluate the accuracy of next-generation sequencing–based quantitative cell-free DNA analysis for fetal antigen genotyping in individuals with alloimmunized pregnancies undergoing clinical testing in practices across the United States as early as 10 weeks of gestation, with the objective of identifying individuals with pregnancies at risk for hemolytic disease of the fetus and newborn and guiding management. METHODS: This prospective cohort study included patients with alloimmunized pregnancies undergoing clinical fetal antigen cell-free DNA analysis between 10 0/7 and 37 0/7 weeks of gestation at 120 clinical sites. Both the pregnant person with the alloimmunized pregnancy and the neonates resulting from the pregnancies were included. The laboratory issued the cell-free DNA results prospectively as a part of clinical care. After delivery, neonatal buccal swabs collected between 0 and 270 days of life were sent to an outside independent laboratory for antigen genotyping. The outside laboratory was blinded to the fetal cell-free DNA results, and the results were compared. Concordance was reported for the fetal antigen cell-free DNA analysis for antigens to which the pregnant person was alloimmunized and for all antigens for which the pregnant person was genotype negative. RESULTS: A total of 156 pregnant people who received clinically ordered cell-free DNA fetal antigen testing provided neonatal buccal swabs for genotyping after delivery. Overall, 15.4% of participants were Hispanic, 9.0% were non-Hispanic Black, 65.4% were non-Hispanic White, 4.5% were Asian, 1.3% were more than one race or ethnicity, and 4.5% were unknown. The median gestational age at the time of testing was 16.4 weeks with a median fetal fraction of 11.1%. Concordance between cell-free DNA analysis results and neonatal genotype was determined for 465 antigen calls for the following antigens: K1 (n=143), E (124), C (60), Fy a (50), c (47), and D(RhD) (41). These 465 calls included 145 in which the fetus was antigen positive and 320 in which the fetus was antigen negative. We observed complete concordance between prenatal fetal antigen cell-free DNA analysis results and neonatal genotypes for the 465 calls, resulting in 100% sensitivity, specificity, and accuracy. CONCLUSION: In a diverse multicenter cohort, cell-free DNA analysis was highly sensitive and specific for determining fetal antigen genotype as early as 10 weeks of gestation in individuals with alloimmunized pregnancies. Taken together with previously published evidence, this study supports the implementation of cell-free DNA testing to manage individuals with alloimmunized pregnancies in the United States.