Color Doppler imaging of the uterine artery

Color Doppler ultrasound and spectral Doppler imaging of the uterine artery is an important part of any obstetric Doppler imaging. The uterine arteries of both sides must be visualized first on color flow imaging, by tracing these vessels as they cross the external iliac artery and vein of each side. The uterine artery can sometimes be elusive for the novice; the trick I use, is to trace the full length of the external iliac vessels from the inguinal region upwards in long axes. This leads to a strange, but prominent artery crossing the iliac artery and vein in an oblique X manner- this is the uterine artery. Spectral Doppler trace will confirm the nature of the uterine artery. (The color Doppler video clip above shows the Right uterine artery in a 14 week old gestation).
When should the uterine artery be imaged? The uterine artery must be imaged from as early as 11- 14 weeks onwards to rule out/ predict a high risk pregnancy. 
Normal PI values at 11 to 13 weeks are usually greater than 2.5. However, lower PI and RI values may be seen on the ipsilateral side as the placenta (ie: if the placenta is located to the right lateral region of the uterus, the right uterine artery would have far lower PI and RI values than the left uterine artery).
The spectral Doppler trace below shows normal values in a 24 week old pregnancy:

With values of PI= 0.76 and RI of 0.5, this uterine artery is normal for 24 weeks.











Bifurcation of the uterine artery (normal anatomical variants of the uterine artery):

 

This patient showed a division (bifurcation) of the right uterine artery (see color Doppler video above), with both vessels seen crossing over the external iliac vessels of that side. The uterine artery is known to divide or in some cases to be duplicated on one or both sides. Both branches of the uterine artery on the right side are seen to lead to the parent vessel in the video above.  

References:
                 1) Uterine artery Doppler study in ICSI (intra-cytoplasmic sperm injection) pregnancies (free article)
                 2)  Doppler Study uterine artery of 17 to 24 weeks gestation in advanced maternal age
                 3)  Role of uterine artery Doppler in determining those women at risk of placental insufficiency -   this is an excellent article from centrus.com
                4) http://www.ultrasound-images.com/fetus-general.htm#Color_Doppler_imaging_of_the_uterine_artery