Relationship between the placental location and the flow velocity waveforms of bilateral uterine arteries.

The relationship between the placental location and the resistance index (RI) of the ascending branch of bilateral uterine arteries was examined with continuous Doppler ultrasonography, in 48 healthy pregnant women in the 37th to 40th week of gestation. When the placental location was central, there was little difference in the RI between the right and left uterine artery (fundus; 0.61 +/- 0.04 versus 0.58 +/- 0.03, NS, body; 0.48 +/- 0.04 versus 0.47 +/- 0.03, NS, and lower segment; 0.28 +/- 0.03 versus 0.30 +/- 0.04, NS). The RI became smaller when the level of placental attachment was lower toward the cervix. In cases where the placental location has shifted to the right or left of the uterine body, the RI on the placental side was smaller than that of the contralateral uterine artery (0.39 +/- 0.04 versus 0.62 +/- 0.03, p less than 0.01). The physiological and clinical significance of these results are discussed in the following report.