RESUMEN
Color pulsed Doppler ultrasound was used to examine the uterine arteries of a total of 265 normal pregnant women during 22-28 weeks' gestation at the Division of Maternal-Fetal Medicine, King Chulalongkorn Memorial Hospital. Reference ranges for pulsatility index (PI) were determined and throughout this gestational range, the mean values were nearly constant and lower than 0.9 and the upper limit of 95 per cent confidence interval (CI) for the PI values were lower than 1.0. In conclusion, the authors have established the reference ranges for PI of uterine arteries in the late second to early third trimester of pregnancy in Thai pregnant women. This could be beneficial for the baseline data in the evaluation of pregnant women complicated with preeclampsia and fetal growth restriction.