Rate of future hemolytic disease of the fetus and newborn following the prehospital transfusion of RhD-positive blood products to females of childbearing potential in the United States of America

OBJECTIVES Transfusing females of childbearing potential (FCP) in hemorrhagic shock with RhD-positive blood products risks inducing the formation of anti-D that can cause hemolytic disease of the fetus and newborn (HDFN) in future pregnancies. A previous study found that 957 FCPs were transfused with RhD-positive blood products over approximately 5-years in the United States (U.S.) in the prehospital phase of their resuscitation. This study used an in silico simulation to calculate the rate of future HDFN amongst these 957 transfused FCPs.METHODS A model that calculated the overall risk of any severity of HDFN was updated with the most current nativity data in the U.S. population. The model first simulated 1,000 FCPs of unknown RhD type at each age between 12-50 years to determine their age-specific rate of future HDFN. This model was instantiated 500 times representing a total of 19.5 million simulated FCPs. The model then used the IQR of the median ages of the 957 transfused FCPs, stratified by U.S. geographic region, to simulate the future HDFN outcomes of these FCPs. This model was instantiated 500 times representing approximately 2,500 years.RESULTS The maximum rate of HDFN for FCPs of unknown RhD type was approximately 0.8% and occurred when the FCPs were between ages 18-20 years. The risk of future HDFN for the 957 RhD-type unknown transfused FCPs ranged from 0.214% (Northeast) to 0.294% (South) per year. Over this 2,500 year simulation a total of 1,368 HDFN cases were calculated to occur (0.55 per year). The number of prehospital transfused FCPs was not equal between the geographic regions and ranged between 29 (Northeast) to 710 (South) every 5-years. Thus, based on the historical trends in these four geographic regions, one case of HDFN would be expected to occur every approximately 2.4- to 80.7-years depending on the geographic region.CONCLUSIONS Due to the generally advanced maternal age of the 957 transfused FCPs and their low probability of being RhD-negative, the risk of future HDFN because of urgent prehospital RhD-positive transfusion is low.