PURPOSE: to test a new, noninvasive method for the diagnosis of fetal anemia in red blood cell isoimmunized pregnancies. METHODS: the index obtained by the ratio between the ultrasonographic measurement of the biventricular outer dimension (BVOD) and femur length (both in centimeters) was correlated with fetal hemoglobin values in a cross-sectional study. Fifty-nine fetuses of isoimmunized pregnancies selected for invasive treatment and submitted to 130 cordocenteses for the diagnosis and treatment of anemia were included in the study. The cardiofemoral index was obtained immediately before the cordocentesis and the fetal hemoglobin index was obtained from fetal blood samples. Linear regression was carried out to assess the correlation between the index and fetal hemoglobin; ROC curve was applied to determine the most accurate cutoff for the diagnosis of the fetal hemoglobin concentration below 10g/dl. RESULTS: BVOD measurement varied from 1.6 to 4.7 cm (average 2.5±1.3cm), and length of the femur, from 3.0 to 6.9 cm (average 4.3±0.9 cm). The cardiofemoral index varied from 0.4 to 1.0 (average 0.6±0.1). A significant inverse correlation between the cardiofemoral index and fetal hemoglobin (R²=0.37 and p<0.0001) was observed. The cutoff of 0.60 was the best to predict a level of fetal hemoglobin below or equal to 10.0g/dl: 80.85% sensitivity, 83.13% specificity, 73.8% positive predictive value, and 88.46% negative predictive value, in the diagnosis of fetuses anemia. CONCLUSION: the cardiofemoral index allows for good accuracy in the prediction of fetal hemoglobin concentration below 10g/dl in red blood cell isoimmunized pregnancies. It may thus be applied as a noninvasive method to the diagnosis of this pathology.
RH Isoimmunization; Anemia, neonatal; Ultrasonography; Period analysis
