Fetal distress is a progressive state of fetal asphyxia, which if not corrected will result in decompensation of the physiologic responses and cause permanent central nervous system and other damage or death. When stressful stimuli persist, the fetus responds by slowing its heart rate, constricting its peripheral circulation and maintaining a continuous blood flow to its adrenal glands, head, heart and umbilical circulation. Methods of antepartum fetal assessments based on a single variable recording [e.g NST] are subject to certain unavoidable errors. A non-reactive NST may be a very late sign of fetal compromise. Gauging fetal condition by the dynamic study of a number of functions is the aim of the biophysical profile study using the real time ultrasound. Doppler ultrasound now offers obstetricians the potential to evaluate uteroplacental and fetal blood flow serially and so increase our understanding of the pathophsiology of complicated pregnancy. Doppler studies of the fetal circulation in IUGR and hypoxia have demonstrated increased resistance to flow in the umbilical arteries and redistribution in the fetal circulation with reduced resistance and increased velocity in the internal carotid and middle cerebral arteries and the opposite in the descending thoracic aorta. Fetal Doppler studies may on the one hand help to determine the optimal time for delivery, while on the other allow the pregnancy to continue as long as possible to gain fetal maturity, thus a voiding obstetrical emergency situations and fetal damage. In the Doppler study, the S/D ratio will become infinity once diastolic velocities reach zero, while RI approaches one, but PI will continue to show change even with no diastolic flow, causing it to be favoured by some investigators. Recent studies show that uteroplacental Doppler studies are no more specific or sensitive for the detection of growth retardation in a screening setting than conventional fetal biometric measurements [HC/AC ratios]. Positive predictive values for the detection of growth retardation range from 17-53 %. Reverse end diastolic flow velocity in the umbilical artery suggests extreme abnormality in waveform and resistance and is associated with catastrophic pregnancy outcome with prenatal mortality approaching 5 %, and aggressive perinatal management may be advised in this condition. The presence of reverse flow in the fetal descending aorta appears to represent very severe fetal compromise with a very high mortality.