Create reference centile charts for Doppler study of Pulsatile index (PI), Resistance index (RI) and Systolic to Diastolic (S/D) ratio ofumbilical artery in Thai fetus throughout gestation.Six hundred fifty eight pregnant women between 13-40 weeks gestation who attended the antenatal clinic at Siriraj Hospital, Mahidol University, Bangkok, were recruited. Each fetus was measured only once for the purpose of the present study. The mean and fitted centiles were estimated at each week of gestation using linear regression modeling.Doppler study of Pulsatile index (PI), Resistance index (RI), and Systolic to Diastolic (S/D) ratio of umbilical artery were measured in 658 fetuses. The mean 95% confidence intervals for Doppler study of Pulsatile index (PI), Resistance index (RI), and Systolic to Diastolic (S/D) ratio of umbilical artery at each gestational age were fitted to estimate by linear regression models. The centile chart of this parameter was also presented.Reference centile chart for Doppler study of Pulsatile index (PI), Resistance index (RI) and Systolic to Diastolic (S/D) ratio of umbilical artery of Thai fetuses was presented.