Fetomaternal hemorrhage: evaluation of recurrence within a large integrated healthcare system.

Background: Fetomaternal hemorrhage is associated with severe fetal morbidity and mortality. The recurrence risk of fetomaternal hemorrhage is unknown.

Objective: We sought to establish the recurrence rate of fetomaternal hemorrhage in a large integrated healthcare system over a 10-year period.

Study Design: In this retrospective study within the Kaiser Permanente Northern California medical system, cases of fetomaternal hemorrhage were defined by either an elevated fetal hemoglobin level as determined by flow cytometry for a concerning pregnancy outcome (preterm delivery, perinatal demise, neonatal anemia, or transfusion within the first 2 days of life) or by perinatal demise with autopsy findings suggestive of fetomaternal hemorrhage. The outcomes of subsequent pregnancies were reviewed for features of recurrence.

Results: Within the 2008 to 2018 birth cohort of 375,864 pregnancies, flow cytometry testing for fetal hemoglobin levels was performed in 20,582 pregnancies. We identified 340 cases of fetomaternal hemorrhage (approximately 1 in 1100 births). Within the cohort of 340 affected pregnancies, perinatal loss was recorded for 80 (23.5%) pregnancies and 50 (14.7%) pregnancies delivered neonates who required transfusion. The affected patients had 225 subsequent pregnancies of which 210 were included in the analysis. Of these, 174 (82.9%) advanced beyond the threshold of viability and were delivered within our healthcare system. There was 1 case of recurrent fetomaternal hemorrhage identified. The recurrent case involved a spontaneous preterm delivery of an infant who was noted to have an elevated reticulocyte count but was clinically well.

Conclusion: Within our large integrated healthcare system, approximately 1 in 1100 pregnancies was affected by fetomaternal hemorrhage within a 10-year period, which is comparable with previous studies. We identified 1 case of recurrence, yielding a recurrence rate of 0.5%. This infant did not have features of clinically important fetomaternal hemorrhage. This information can inform counseling of patients with affected pregnancies.