Rh Sensitization and Induced Abortion —Reply

In Reply In response to our recent article, Mr Uzoigwe and Dr Ali comment that the 1965 study by Zipursky et al, which we used to calculate a threshold for significant fRBC allosensitization, is unethical. These ethical flaws highlight that decades have elapsed since there has been adequate scientific study of Rh sensitization in early pregnancy and underscore the need to design new studies that address research gaps while protecting human participants, as we did. Second, while we agree that the threshold of 0.1 mL of fRBCs may be arbitrary, this threshold led to sensitization in only 4 of 15 participants in the study by Zipursky et al after repeated exposures. In contrast, antigenic exposure prior to early abortion in our study was likely to be very limited. The suggestion that subthreshold circulating fRBCs in early pregnancy could cause sensitization without an inciting event is inconsistent with current practice. No guidelines recommend giving Rh immunoglobulin during the first trimester without bleeding, as Uzoigwe and Ali imply. Regardless of the sensitization threshold, our research showed that fRBC levels did not change after abortion at less than 12 weeks, demonstrating that neither medication nor early procedural abortion are risk factors for maternal exposure to fRBCs. We acknowledge that it is theoretically possible that fRBCs may be transferred with less immunogenicity when injected intravenously than via fetal loss, but this is untested. Additionally, the increa...
Source: JAMA - Category: General Medicine Source Type: research