RH disease management: Has Doppler replaced amniotic fluid assessment?

Perhaps so. Measuring middle cerebral artery (MCA) peak velocity on Doppler ultrasound is significantly better at predicting severe fetal anemia than traditional assessment via amniotic fluid ΔOD450, says a well-designed clinical trial involving a large cohort of fetuses. In addition, it's noninvasive and can safely replace the AF assessment in managing Rh-alloimmunized pregnancies.

Researchers were looking for a diagnostic test that would avoid the invasiveness of standard management-which involves evaluation by U/S for hydrops and serial amniocentesis for bilirubin values. In a prospective, international multicenter study of a cohort of consecutive Rh-D, c, E, and Fy^a alloimmunized pregnancies with titers at or above 64 and antigen-positive fetuses, investigators performed both the MCA Doppler and AF tests at the same time in all patients and compared results with the gold standard of fetal or cord blood sampling (at birth) to gauge the actual hemoglobin.

In a total of 165 fetuses, MCA Doppler accurately predicted severe anemia in 65/74 fetuses that were determined to be severely anemic (88%), with a specificity of 82%, and a positive predictive value of 80%. In contrast, AF had a sensitivity of 76%, specificity of 77%, and a positive predictive value of 73%.