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. 1. Introduction Maternal alloimmunization still affects a large number of pregnancies, particularly in developing countries [1, 2]. These pregnancies need specific follow-up at tertiary referral centers to carry out proper monitoring, in the view of a high risk of perinatal morbidity and mortality [3, 4]. When severe fetal anemia is suspected by a noninvasive method, cordocentesis is necessary to assess fetal hemoglobin concentration and then to determine the need of an intrauterine transfusion (IUT) [5, 6]. In this context, perinatal outcome also will depend on timely diagnosis and treatment of fetal anemia. For severely anemic fetuses the transfusion therapy is a life-saving procedure [7–9]. However, IUT carries risks for both mother and fetuses. In this way, it is important to determine which fetus is anemic and so it will need an IUT [7–9]. In this high-risk context, assessment of the degree of fetal anemia is an essential strategy for managing these pregnancies [10]. There are three main references for diagnosis and classification of fetal anemia. The first one was proposed by Nicolaides et al., published in 1998 [11]. These criteria use fetal hemoglobin deviation or deficit (mean hemoglobin for gestational age minus measured hemoglobin) as