REFERENCE RANGES AND ULTRASONOGRAPHIC EXPOSURE CONDITIONS FOR PULSED DOPPLER SONOGRAPHIC STUDIES OF THE FETAL INTERNAL CAROTID-ARTERY

We describe the 5th to 95th percentiles for the resistive index from t he fetal internal carotid artery and measurements of (1) scanning time and (2) axial distance between transducer face and the fetal skull du ring pulsed Doppler examinations. Cerebral resistance peaks at 30 week s' gestation and declines thereafter. The median duration of pulsed Do ppler exposure was 31 seconds (range, 4-80 seconds), and the median tr ansducer-skull distance was 2.2 cm (range, 1.3-6.2 cm). Our data provi de reference ranges covering the entire period of fetal viability and help define ultrasonographic exposure conditions during pulsed Doppler examinations of fetal intracranial vessels.