The aim of this study was to ascertain the value of serially performed Doppler sonographic measurements of fetal vessels for the prediction of FHR alterations in labor a longitudinal analysis was conducted. 24 patients with SGA fetuses as the only risk factor and 38 patients without any risk factor were recruited for the study. Flow velocity waveforms of the fetal aorta and the umbilical artery were analyzed for systolic diastolic (S/D) ratio weekly at 20-39 weeks gestation and from 30 weeks gestation onwards twice weekly. Courses were related to complications during labor reflected by alterations of FHR tracings. The more numerous pathologie S/D ratios of both fetal vessels were recorded the more frequently complications in labor occurred (Chi Square test, p < 0.05). The mean value of the S/D ratios in fetuses with FHR pathology in labor differed significantly compared to the uncomplicated group (Wilcoxon rank sum test, p < 0.05). The fluctuation of S/D ratios was greater in the complicated than in the normal group (Wilcoxon rank sum test, p < 0.05). A combination of parameters describing S/D ratios showed a sensitivity of 86% and a specificity of 19% for the fetal aorta and a sensitivity of 71% and a specificity of 91% for the umbilical artery. Serial Doppler measurements of the fetal aorta and the umbilical artery aid in predicting pathologic FHR alterations in labor and may be of benefit in antenatal care to ensure fetal well being particularly in cases of IUGR.