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 less than 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 assessment

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
Pulsatility index (PI)

This is calculated by the following equation:

  • PI = (peak systolic velocity - end diastolic velocity) / time averaged velocity = (PSV - EDV) / TAV
Abnormal patterns include
  • persistence of a high resistance flows throughout pregnancy
  • persistence of notching throughout pregnancy
  • reversal of diastolic flow throughout pregnancy: severe state​
Ultrasound - obstetric
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Article Information

rID: 2247
System: Obstetrics
Section: Approach
Synonyms or Alternate Spellings:
  • Uterine arterial Doppler ultrasound assessment
  • Uteroplacental Doppler flow assessment
  • Uteroplacental Doppler assessment
  • Utero-placental Doppler assessment
  • Utero-placental blood flow assessment

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