The usefulness of middle cerebral artery Doppler assessment in the treatment of the fetus at risk for anemia.

The use of Doppler ultrasound evaluation to measure the peak systolic velocity of the fetal middle cerebral artery (MCA) has been a major breakthrough in the noninvasive detection of fetal anemia. An elevated peak MCA velocity of >1.5 multiples of the median is useful in the timing of the initial intrauterine transfusion (IUT) in the red cell-alloimmunized pregnancies. Data reported to date suggest that a threshold of 1.32 multiples of the median can be used to time the second IUT; the MCA Doppler evaluation does not appear sensitive for the timing of subsequent IUTs in these pregnancies. The peak MCA velocity has also proved useful in the detection of other anemic states that include Kell alloimmunization, fetal parvovirus infection, fetomaternal hemorrhage, alphathalassemia, and after-laser therapy for twin-twin transfusion.