Doppler study of the fetal vertebral and middle cerebral arteries in fetuses with normal and increased umbilical artery resistance indices

Objective: To compare the brain sparing mechanism of the fetal vertebral artery (VA), with the one of the middle cerebral artery (MCA) in fetuses with increased umbilical artery (UA) Doppler impedance. Method: We retrospectively studied 1084 Doppler examinations of the VA, MCA and UA performed in 1084 fetuses between 19 and 41 week of gestation. These were divided into 3 groups according to the UA resistance index (UA RI): group 1: UA RI < 95th percentile (N = 965), group 2: UA RI > 95th percentile (N = 111) and group 3: absent UA diastolic flow (N = 8). Afterwards, values were converted into multiples of the median (MoM), and means and standard deviations were calculated. Finally, Kruskal-Wallis tests and box and whiskers charts were applied to evaluate differences. Results: For both, the VA RI and MCA RI, no differences were seen among the groups of fetuses who maintained diastolic flow in the UA. However, the VA RI and MCA RI were lower when the UA diastolic flow was absent. Conclusion: The VA and MCA work in unison, decreasing impedances only when UA flow is severely affected. (c) 2012 Wiley Periodicals, Inc. J Clin Ultrasound, 2013