Objective:To monitor the fetal condition with measurement of resistance of placental vessels and placental function by Doppler Sonography.Methods:The systolic peak velocity (S) and end diastolic velocity (D) were measured by Doppler Sonography at three sites along the umbilical cord:near the fetal abdominal wall insertion (A),in the freefloating midcord (M) and near the placental site (P). The S/D ratio at each site was calculated.Results:In normal cases the mean values of S/D ratio measured at different sites were not the same, being highest at A, lowest at P. With the increase of gestational age, the S/D value steadily decreased. 32 cases with hypertension of pregnancy showed high S/D value at three sites. In 30 cases the S/D value at the site of umbilical cord around neck was similar to that of M.Conclusions:We therefore consider that the use of S/D ratio measurement by Doppler ultrasonography is a relatively effective method for the surveillance of high risk fetus.