Ultrasound assessment of the fetal middle cerebral artery peak systolic velocity: A comparison of the near-field versus far-field vessel.

Objective: Doppler assessment of the fetal middle cerebral artery peak systolic velocity may obviate the need for more invasive procedures in the alloimmunized patient. The purpose of this study was to compare middle cerebral artery peak systolic velocity measurements in the near field and far field.

Study Design: Patients between 16 and 42 weeks of gestation with normal fetuses were eligible (n=151). Peak systolic velocity measurements were obtained at the proximal portion of each middle cerebral artery at its origin in the internal carotid artery, as well as the most distal portion before its division, for a total of 4 measurements per fetus. Comparisons were made among the 4 locations and the data were analyzed using a mixed-model analysis of variance adjusted for gestational age. Results were presented using both P values and 95% CIs. P values <.05 were considered statistically significant. Where appropriate, P values and 95% CIs were adjusted using the Tukey multiple comparison procedure. A subanalysis was performed using 11 patients to assess interobserver reliability, which was calculated using the intraclass correlation coefficient (ICC).

Results: All four measurements were obtained for 120 fetuses (79%). The mean gestational age was 27.0 weeks. Statistically significant differences were noted between distal sites (95% CI, -0.05 to 0.01; P<.01) as well as the two sites on each vessel (95% CI, 0.03-0.07 and 0.07-0.12; P<.001 for both vessels). There was no significant difference between the two proximal locations (95% CI, -0.01 to 0.03; P=0.77).

Conclusion: By which of the 2 vessels the fetal middle cerebral artery peak systolic velocity is affected is selected, as well as the location on the vessel. If the near-field proximal site cannot be interrogated, the far-field proximal site may be the best alternative.