Objective: to assess the value of uterine artery and umbilical artery resistance indices changes in  predicting cases of PTD Setting: The study was carried on gravid women attending AI zahraa University Hospital between February 2009 to September 2010.  Design: A prospective study on gravid women picked up at 24 week gestation during ANC . They were subjected to Doppler velocimetry study of the Umbalical & Uterine artery blood flow to measure the resistive indices changes on going GA. Patients & Methods: Participants were 24 weeks pregnant with a singleton pregnancy, Participants were seen at three study visits: at recruitment, at, 28 weeks gestation; and finally at 34 weeks gestation. Patients who later developed PTL formed the study group n=28. The control group were the women who completed 40 weeks gestation at the time of delivery. For each patient seen at the three visits Doppler velocimetry ultrasound study of the umbilical and uterine were performed to assess  the RI indices changes. Results: The current study revealed a high significant difference in the RI value of the umblical artery starting from 28 weeks visit to be (0.74), (0.61) in the study group and control group respectively with p-value (0.001) also a highly significant diff. were noticed at the 34 weeks visit to be( 0.65),(0.49) in the study group and control group respectively with p-value (0.0001). As regard the uterine artery RI the study group showed a highly significant difference at 28 weeks visit when compared to the value of the control group with p-value( 0.001) in the same manner the RI value at 34 weeks visit showed a highly significant difference between both groups with p-value(0.0001).In the current study the mean RI for both uterine and umbilical arteries decreased steadily across all study visits from 24 weeks to 34 weeks gestation. In linear regression models, the relationships of both uterine and umbilical artery RI with gestational age were significantly different between study group and control group. The mean umbilical artery RI  and uterine artery RI indices decreased significantly more slowly across gestation for study group than for control group. In univariate analyses, a 2.9 fold increase in risk for PTD was associated with a 0.1 unit increase in uterine artery RI across gestation; while a 3.4 fold increase in risk for PTD was associated with a 0.1 unit increase in umbilical artery RI across gestation. Conclusion: The RI indices values in the umblical artery and uterine artery showed a significant slowly decrease along gestational age among gravid patients developed preterm labour so that they could be predictive for PTL.