Simultaneous use of Doppler ultrasound and electromagnetic flow probes in fetal flow assessment.

A placental embolization model in the fetal lamb was used to examine the relationship between acute and chronic alternations in placental vascular resistance and changes in flow velocity waveforms as measured by Doppler and electromagnetic flow probes. The peak systolic to end-diastolic (S/D) ratio measured by these techniques was .885 and the correlations between Doppler S/D ratio and placental vascular resistance in the acute and chronic situations were .86 and .339, respectively. This preliminary data suggest that flow velocity waveforms are independent of the method used and that remarkable differences occur in the placental microcirculation during acute and chronic embolization.