A new non-invasive method for measuring uterine vascular resistance and its relationship to uterine artery Doppler indices: a longitudinal study.

OBJECTIVES

To describe a new method for measuring uterine vascular resistance (R(uta) ), establish longitudinal reference ranges and explore the relationship between uterine artery (UtA) Doppler indices and R(uta) .

METHODS

This was a longitudinal study of 53 low-risk pregnancies. Doppler ultrasonography was used to measure UtA velocities, and the pulsatility index (PI), resistance index (RI) and systolic/diastolic velocity (S/D) ratio were calculated. R(uta) was calculated as a ratio between maternal mean arterial pressure and UtA time-averaged maximum velocity.

RESULTS

At 22 + 0 to 39 + 6 weeks of gestation, the mean R(uta) decreased from 1628 to 1180 dyne.s/cm(3) (P < 0.0001). UtA velocities increased (P < 0.0001), whereas the PI (0.79-0.56), RI (0.51-0.40) and S/D ratio (2.0-1.7) decreased (P < 0.0001). R(uta) and the UtA Doppler indices were positively associated (P = 0.003-0.001).

CONCLUSION

We describe a non-invasive method for measuring R(uta) and provide reference ranges for serial evaluation of UtA velocities, Doppler indices and R(uta) .