Diagnosis of severe fetal anemia based on perinatal outcomes: a comparative analysis of the current reference values

Objectives. To compare current criteria for severe fetal anemia diagnosis. Methodology. A cohort study analyzed 105 alloimmunized fetuses that underwent cordocentesis due to risk of anemia. Concordance among the diagnostic criteria for severe fetal anemia, hemoglobin deficit >7 g/dL, hemoglobin deficit ≥5 g/dL, and hemoglobin concentration <0.55 MoM, was analyzed using Cohen's Kappa index. Perinatal mortality, fetal hydrops, and fetal acidosis were used to discuss discordances. Results. There was fair concordance among the three criteria analyzed: 0.80 (Kappa index, IC 95%: 0.67 to 0.93) when comparing hemoglobin deficit >7.0 g/dL and hemoglobin concentration <0.55 MoM criteria, 0.63 (Kappa index, IC 95%: 0.47 to 0.69) when comparing hemoglobin deficit ≥5.0 g/dL and hemoglobin deficit >7.0 g/dL reference, and 0.77 (Kappa index, IC 95%: 0.64 to 0.90) when comparing hemoglobin deficit≥5.0 g/dL and hemoglobin concentration <0.55 MoM standards. Eighteen cases were classified differently depending on the criteria used. The cut-off point of hemoglobin deficit ≥5 g/dL was the best criterion to discriminate fetuses with poor perinatal outcome in our study. Conclusions. Relevant discordances in classification of severe fetal anemia were pointed out. Some criteria may underestimate the real gravity of fetal anemia.