817: Previable “provoked” fetomaternal hemorrhage may represent insensible cell exchange

Abstract

To quantify spontaneous and provoked maternal fetal cell exchange in the first half of pregnancy. Transfer of fetal red blood cells (FRBCs) into the maternal circulation during the previable period is poorly characterized but of clinical relevance for miscarriage management and invasive procedures. Prospective, descriptive cohort study of women presenting for surgical termination of pregnancy with sonographically confirmed gestational age (GA). Pre-procedural (1-2 days prior to procedure) and post-procedural (5 minutes after placental extraction) blood samples were collected to characterize both spontaneous and provoked cell exchange. Samples were analyzed via flow cytometry to quantify FRBCs present in the maternal sample with a sensitivity to 4.3 FRBCs per 10,000 maternal red blood cells. A total of 78 patients at 6-22 weeks GA contributed 156 matched pre- and post-procedural samples. FRBCs were identified in 48 patients (62%) including 3 (4%) who exhibited FRBCs pre-procedure only and 5 (6%) post-procedure only, for a total of 45 patients (58%) having post-procedural FRBCs. Of all the patients with FRBCs following their procedure, the majority (n=40, 89%) also exhibited evidence of cells before the procedure with only 5 patients (11%) exhibiting FRBCs only after. Of the 40 concordantly positive patients, 24 (60%) demonstrated an increase in the cell count, 14 (35%) demonstrated a decrease in the cell count, and 2 (5%) demonstrated an equivalent value (Figure 1). No dose-response relationship was appreciable between GA and FRBC count (Figure 2). Following all patients undergoing disruption of the placenta with instrumentation, just over half of patients had detectable FRBCs in the maternal circulation following their procedure but—among those that did—the majority were also present prior to the procedure. This leads to further questions regarding the relationship between risk events and alloimmunization potential in the first half of pregnancy as the rate of spontaneous transplacental cell exchange may be underappreciated and the magnitude of provoked transfer may be overestimated.View Large Image Figure ViewerDownload Hi-res image Download (PPT)