Cardiofemoral index as an ultrasound marker of fetal anemia in isoimmunized pregnancy

ObjectiveTo test a new noninvasive ultrasound method for diagnosing fetal anemia in red blood cell isoimmunized pregnancies.MethodsA diagnostic accuracy study was carried out to determine the cutoff point of an ultrasound measurement, the cardiofemoral index (CFI), calculated using the biventricular outer dimension (BVOD) and femur length to diagnosis severe anemia. The CFI measurement was performed before each of the 336 cordocenteses on 131 fetuses. Diagnosis test analysis and receiver–operating characteristics (ROC) curves were used and the area under the curve (AUC) was calculated to compare the overall accuracy of the CFI for anemia diagnosis, between fetuses with or without previous intrauterine transfusions (IUT).ResultsAt first cordocentesis (n = 131) the AUC was 0.75 (95% CI, 0.66–0.84). For cases where fetuses had undergone 1 previous transfusion (n = 88) the AUC was 0.76 (95% CI, 0.64–0.88) and at the time of the third cordocentesis for IUT (n = 53) it was 0.73 (95% CI, 0.59–0.86). For a 0.59 CFI threshold to diagnosis fetuses with hemoglobin deficit above 5 g/dL, sensitivity values were 87.2%, 88.0%, and 94.1% respectively for fetuses without IUT, with 1 IUT, and with 2 IUTs. Likelihood ratios for positive (LR+) and negative (LR−) test results were 1.98, 2.05, 1.69 and 0.23, 0.21, 0.13 respectively.ConclusionThe cardiofemoral index may be an effective noninvasive marker of severe fetal anemia in high-risk fetuses, with accuracy similar for fetuses either with or without previous transfusions.