Longitudinal survey of blood flow at three different locations in the middle cerebral artery in normal fetuses

Objectives To assess vascular impedance at three different locations in the middle cerebral artery (MCA) in normal fetuses throughout gestation. Materials and methods Uncomplicated singleton pregnancies at 15–40 weeks' gestation in which Doppler surveys of both MCAs could be obtained were recruited. The pulsatility index (PI) and resistance index (RI) of the proximal, mid and distal sites of both MCAs were measured. The five gestation periods at which the Doppler surveys were performed were (i) 15–19 completed weeks; (ii) 20–24 completed weeks; (iii) 25–29 completed weeks; (iv) 30–34 completed weeks; (v) 35–39 completed weeks. Results A total of 42 fetuses were recruited. The average PI/RI values of the proximal, mid and distal MCA were 1.61/0.82, 1.77/0.82, and 1.84/0.84, respectively. The PI value of the proximal MCA was lower than that of the mid and distal MCA. The PI values of the mid and distal MCA showed no difference. The RI value of the MCA from the three locations also showed no difference. The PI/RI values of MCA for each gestational phase were: (i) 1.81/0.87; (ii) 1.79/0.86; (iii) 1.78/0.86; (iv) 1.70/0.81; (v) 1.62/0.77, respectively. Decreased PI/RI values were observed after 30 weeks' gestation. Conclusions The PI values of the proximal MCA are lower than those of the mid and distal MCA. A marked decrease in PI/RI values was observed after 30 weeks' gestation. Copyright © 2001 International Society of Ultrasound in Obstetrics and Gynecology