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' g estation in which Doppler surveys of both MCAs could be obtained were recru ited. The pulsatility index (PI) and resistance index (RI) of the proximal, mid and distill sites of both MCAs were measured. The five gestation perio ds at which the Doppler surveys were performed were (i) 15-19 completed wee ks; (ii) 20-24 completed weeks; (iii) 25-29 completed weeks; (iv) 30-34 com pleted weeks; (v) 35-39 completed weeks. Results A total of 42 fetuses were recruited. The average PI/RI values of t he proximal, mid and distal MCA were 1.61/0.82, 1.77/0.82, and 1.84/0.84, r espectively. The PI value of the proximal MCA was lower than that of the mi d and distal MCA. The PI values of the mid and distal MCA showed no differe nce. The RI value of the MCA from the three locations also showed no differ ence. The PI/RI values of MCA for each gestational phase were: (i) 1.81/0.8 7; (ii) 1.79/0.86; (iii) 1.78/0.86; (iv) 1.70/0.81; (v) 1.62/0.77, respecti vely. Decreased PI/RI values were observed after 30 weeks' gestation. Conclusions The PI values of the proximal MCA are lower than those of the m id and distal MCA. A marked decrease in PI/RI values was observed after 30 weeks' gestation.