Doppler Ultrasonography versus Amniocentesis to Predict Fetal Anemia

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When red blood cell alloimmunization takes place during pregnancy, the fetus is at risk of hemolytic anemia, which may lead to hydrops and death as early as 17 weeks gestation. Timely diagnosis and blood transfusions may, however, result in survival rates higher than 90%. Until now, these pregnancies have been monitored by serial amniocentesis to estimate bilirubin levels expressed as the change in optical density at a wavelength of 450 nm (ΔOD 450 ). A noninvasive alternative is to use Doppler ultrasonography to measure the peak velocity of systolic blood flow in the middle cerebral artery. The present prospective international study enrolled women with RhD-, Rhc-, RhE-, or Fy a -alloimmunized pregnancies who had an indirect antiglobulin titer of 1:64 or higher and an antigen-positive fetus. The final study group included 164 pregnancies with 165 fetuses, 74 of whom were severely anemic as defined by a hemoglobin deficit 5 or more standard deviations (SD) below the mean for gestational age. Another 25 fetuses had mild anemia with a deficit 2 to 5 SDs below the mean. Doppler ultrasonography was 88% sensitive in detecting severe fetal anemia (95% confidence interval [CI], 78-93%). Its specificity was 82% (95% CI, 73-89%) and its accuracy was 85% (95% CI, 79-90%). Amniotic fluid ΔOD 450 was 76% sensitive (95% CI, 65-84%), 77% specific (95% CI, 67-84%), and 76% accurate (95% CI, 69-82%). The Doppler study was 12% more sensitive and 9% more accurate than were measurements of amniotic fluid ΔOD 450 . The findings in this large-scale prospective study indicate that invasive testing by amniocentesis can safely be replaced by Doppler measurements of peak systolic blood flow in the middle cerebral artery for detecting severe hemolytic anemia in Rh-alloimmunized pregnancies.