Pulsed Doppler duplex sonography was performed longitudinally on 11 uncomplicated singleton pregnancies from 20 to 41 week's gestation (87 measurements). Blood flow velocities were recorded at 3 locations: abdominal insertion site (O), in the free floating part (C), placental insertion site (PL). The objective of the study was to determine whether the C site S/D ratio, the quickest and easiest to perform, relates to the other sites. The S/D ratio measurements fell from the near abdomen (O) to the free floating part (C) to the placental insertion site (PL) between 25-35 week's gestation. Statistical analysis, including analysis of variance for repeated measures and student t test, showed no significant difference in S/D ratio among the locations before 25 and after 35 week's gestation. The S/D ratio at the O site was significantly higher than at the PL site between 25-35 week's gestation; the C site was not significantly different from the PL site.