Uteroplacental blood flow assessment

Uteroplacental blood flow assessment is an important part of fetal well-being assessment and evaluates Doppler flow in the uterine arteries and rarely the ovarian arteries.

Pathology

In a non-gravid state and at the very start of pregnancy the flow in the uterine artery is of high pulsatility with a high systolic flow and low diastolic flow. A physiological early diastolic notch may be present.

Resistance to blood flow gradually drops during gestation as a greater trophoblastic invasion of the myometrium takes place. An abnormally high resistance can persist in pre-eclampsia and IUGR. If resistance is low, it has an excellent negative predictive value with a <1% chance of developing either pre-eclampsia or having IUGR. A high resistance often equates to a 70% chance of pre-eclampsia and 30% chance of IUGR.

Radiographic features

Ultrasound

The parameters used in the assessment of uteroplacental blood flow include:

• RI = resistive index

• PI = pulsatility index

• presence of persistent diastolic notching

Resistive index (RI)

This is calculated by the following equation:

RI = (PSV-EDV) / PSV = (peak systolic velocity - end-diastolic velocity) / peak systolic velocity 

• normal (low resistance) RI <0.55

• high resistance

  • bilateral notches RI >0.55

  • unilateral notches RI >0.65

Pulsatility index (PI)

This is calculated by the following equation:

• PI = (PSV - EDV) / TAV = (peak systolic velocity - end-diastolic velocity) / time-averaged velocity

Abnormal patterns include

• persistence of a high resistance flow throughout pregnancy

• persistence of notching throughout pregnancy

• reversal of diastolic flow throughout pregnancy: severe state​

External links

• uterine artery PI calculator (>20 weeks' gestation) - The Fetal Medicine Foundation

If any of these links are broken or for other problems and questions, please contact [email protected].