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.

Physiology

In a non gravid state and at the very start of pregnancy the flow in 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 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 the 1% chance of developing either pre-eclampsia or have IUGR . A high resistance often equates to a 70% chance of pre-eclampsia and 30% chance of IUGR.

Sonographic assessment

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

Abnormal patterns include

• persistence of a high resitanceresistance flow throughout pregnancy
• persistence of notching throughout pregnancy
• reversal of diastolic flow throughout pregnancy -: severe state

See also

• umbilical arterial Doppler assessment
  • absent umbilical arterial end diastolic flow
  • reversal of umbilical arterial end diastolic flow
• ductus venosus flow assessment
  • abnormal ductus venosus waveforms
• umbilical venous flow assessment
• fetal middle cerebral arterial Doppler assessment