The prevalence of maternal F cells in a pregnant population and potential overestimation of foeto-maternal haemorrhage as a consequence.

Abstract

Acid elution (AE) is used to estimate foeto-maternal haemorrhage (FMH). However AE cannot differentiate between cells containing foetal or adult haemoglobin F (F cells), potentially leading to false positive results or an overestimate of the amount of FMH. The prevalence of F cells in pregnant populations remains poorly characterised. The purpose of this study was to ascertain the incidence of HbF-containing red cells in our pregnant population using anti-HbF-fluorescein isothiocyanate flow cytometry (anti-HbF FC) and to assess whether its presence leads to a significant overestimate of FMH. Eighty-eight pregnant patients were assessed for the presence of F cells and foetal red cells by AE and anti-HbF FC. The "FMH equivalent", estimated by AE and anti-HbF FC, was calculated. Thirty-six percent of the pregnant population had F-cell populations detectable by anti-HbF FC while AE detected F cells in 48% of the population. The mean estimated FMH equivalent determined by AE and anti-HbF FC was 0.59 mL (0-23.93 mL) and 0.41 (0 to 2.19 mL), respectively (p=0.012). In 3% of our population, AE overestimated the FMH by >3 mL due to the presence of an F-cell population of at least 16%. Thirty-six percent of a prospectively evaluated group of consecutive pregnant women were found to have F-cell populations. In some patients, these findings were clinically significant as AE overestimated the degree of FMH as a consequence.