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Objective: To estimate the accuracy of a new assay to determine the fetal RHD status using circulating cell-free DNA., Methods: This was a prospective, observational study. Maternal blood samples were collected in each trimester of pregnancy in 520 nonalloimmunized RhD-negative patients. Plasma samples were analyzed for circulating cell-free DNA using the SensiGENE RHD test, which used primers for exons 4 and 7 as previously described and incorporated a new primer design for exon 5 of the RHD gene. Neonatal serology for RhD typing using cord blood at birth was undertaken and results were stored in a separate clinical database. After unblinding the data, results of the DNA analysis were compared with the neonatal serology., Results: Inconclusive results secondary to the presence of the RHD pseudogene or an RHD variant were noted in 5.6%, 5.7%, and 6.1% of the first-, second-, and third-trimester samples, respectively. The incidence of false-positive rates for RhD (an RhD-negative fetus with an RHD-positive result) was 1.54% (95% confidence interval [CI] 0.42-5.44%), 1.53% (CI 0.42-5.40%), and 0.82% (CI 0.04-4.50%), respectively. There was only one false-negative diagnosis (an RhD-positive fetus with an RHD-negative result), which occurred in the first trimester (0.32%; 95% CI 0.08-1.78%). Genotyping for mismatches across repeated samples revealed that this error was related to mislabeling of samples from two patients collected on the same day at one of the collection sites. Overall test results were in agreement across all three trimesters (P>.99)., Conclusion: Circulating cell-free DNA can accurately predict the fetal RhD status in all three trimesters of pregnancy.

Background: Fetal-maternal hemorrhage is usually spontaneous and goes undetected but can be associated with adverse perinatal outcomes., Case: We describe the detection of a fetal-maternal hemorrhage by abrupt disappearance of prophylactic anti-D on antibody screen in an Rh-negative mother with dichorionic twins admitted for atrial flutter of one twin. Both rosette and Kleihauer-Betke tests were positive. The diagnosis was confirmed by anemia in one twin at birth., Conclusion: Fetal-maternal hemorrhage requires a high index of suspicion for diagnosis. An unexpected sudden decline in Rh immune globulin-related anti-D may be an indication of fetal-maternal hemorrhage.

The cloning of the RhDCcEe complex has made it likely that the polymerase chain reaction will be incorporated into the modern management of rhesus sensitization. Currently, the accuracy of this technique is under evaluation. Its specific role in management protocols is not yet clear. The use of this technology will hopefully avoid the need for cordocentesis or serial amniocenteses in some patients.