Usefulness of maternal fetal red blood cell count in rhesus-positive pregnant women.

Background Fetal red blood cells (FRBC) in maternal blood are counted in rhesus-negative women to determine the amount of anti-D immunoglobulin to be administered in the case of a rhesus-positive fetus. In rhesus-positive pregnant women this is done in not always very well-defined indications including trauma, miscarriage, fetal death and diminished fetal movements. The aim of this study is to determine if the detection of FRBC is useful in rhesus-positive pregnant woman. This was done by assessing maternal and fetal characteristics that are more likely to give a positive test. Materials and methods This was a retrospective cohort study. Results A total of 169 FRBC tests were performed in 161 rhesus-positive pregnant women. FRBC were found in 45 (26.6%) of the women. Three patients experienced a miscarriage although their FRBC tests were negative (p = 0.295). Of the seven patients who experienced unexpected stillbirths, three tested positive. The deaths were not less likely to occur if the results had been negative (p = 0.631). There was a statistically significant difference between the different types of trauma indications (p = 0.025): the test was more likely positive if there had been a fall on the ground or staircase or blunt trauma (p = 0.041, 0.026 and 0.018, respectively). FRBC were not more frequently present in the absence of fetal movements (n = 16, p = 0.693). Conclusion FRBC in maternal blood were more likely positive in the case of a fall on the ground, or from a staircase. However, a positive test does not necessarily imply fetal pathology and, therefore, does not contribute to clinical management.