Background: Post term pregnancy necessates IOL to avoid the potential hazards on fetal and maternal outcome. Several factors affect the process of IOL, and there is often great uncertainty regarding its success. Late in pregnancy, vasodilatation of fetal brain vessels occurs as a physiological preparation for the onset of labor. MCA-PI decreases in turn as a preliminary fetal mechanism for adaptation to labor.   Objective: We assumed that evaluating MCA-PI prior to IOL may be used as a beneficial tool to predict responders to IOL.   Methodology: A prospective cohort study, which included 150 post term patients (41-42 weeks), who were admitted to Kasr Al-Ainy Hospital for IOL. Prior to induction, we performed U/S to record MCA-PI, together with CL and EFW. Patients were given 25Mcg misoprostol vaginal tab/6 hours, maximum for 24 hours. Responders were defined as those who succeeded to enter the active phase of labor, by the onset of active uterine contractions. Patients who needed CS before the onset of active labor were excluded.   Results: A total of 150 patients were included in the study. 133 cases (88.7%) entered the active phase of labor, while 17 (11.3%) cases failed to enter in the active phase. Both groups were comparable in the parity and BMI. MCA-PI was significantly lower in the responder group (group 1; 1.29± 0.11) compared to the non-responders (group 2;1.67± 0.13). The mean CL was 25.28± 4.25 & 33.43± 4.8 in groups 1&2 respectively. The mean EFW was 3375.47± 178 & 3722.65± 116.33 in groups 1 & 2 respectively. ROC analysis examined the ability of these parameters in predicting the response to IOL. The cutoff values, sensitivity & specificity respectively were; 1.41, 94.12% , 83.46% for MCA-PI, 26.6, 94.1%, 60% for CL, and, 3555, 94%,83.5% for EFW.  WE further included all significant variables (maternal age, MCA-PI, CL, EFW) in a multivariate logistic regression analysis. MCA-PI was a statistically significant predictor for the response to IOL, even after adjustment of the other variables  (P value= 0.05). Conclusion: MCA-PI evaluation prior to IOL is a useful tool in prediction of IOL outcome. Lower PI values may predict successful outcome. CL assessment and EFW are other factors that may predict the outcome of IOL.