Umbilical arterial Doppler assessment

Radswiki et al.

Umbilical arterial (UA) Doppler assessment is used in surveillance of fetal well-being in the third trimester of pregnancy. Abnormal umbilical artery Doppler is a marker of uteroplacental insufficiency and consequent intrauterine growth restriction (IUGR) or suspected pre-eclampsia

Umbilical artery Doppler assessment has been shown to reduce perinatal mortality and morbidity in high risk obstetric situations 5.

As a general rule, a degree of caution should be exercised with the routine use of Doppler in pregnancy, due to the concerns related to heating/thermal effects from the high intensities of Doppler ultrasound.

Assessment of fetal growth and well being in the third trimester, which routinely includes umbilical Doppler assessment is indicated in scenarios where there is increased risk of fetal growth restriction or poor perinatal outcome.

Maternal conditions
Pregnancy related conditions
Doppler ultrasound

The Doppler indices measured at the fetal end, the free loop and the placental end of the umbilical cord are different with the impedance highest at the fetal end. The changes in the indices are likely to be seen at the fetal end first. Ideally the measurements should be made in the free cord. However for consistency of recording in cases being followed up, a fixed site would be more appropriate, i.e. fetal end, placental end or intraabdominal portion.

Waveform

The umbilical arterial waveform usually has a "saw tooth" pattern with flow always in the forward direction. An abnormal waveform shows absent or reversed diastolic flow. Before the 15th week, absent diastolic flow may be a normal finding 6.

The 95% confidence interval limit slowly decreases for both the resistive index (RI) and pulsatility index (PI) through the course of gestation due to progressive maturation of the placenta and increase in the number of tertiary stem villi.

Parameters

The commonly used parameters are:

  • umbilical arterial S/D ratio (SDR): systolic velocity / diastolic velocity
  • pulsatility index (PI) (Gosling index): (PSV - EDV) / TAV
  • resistive index (RI) (Pourcelot index): (PSV - EDV) / PSV
  • PSV: peak systolic velocity 
  • EDV: end diastolic velocity 
  • TAV: time averaged velocity

The Doppler indices have been found to decline gradually with gestational age:

  • S/D ratio mean value decreases from 3.560 to 2.511
  • RI mean value decreases from 0.756 to 0.609
  • PI main value decreases from 1.270 to 0.967
Classification of severity

In growth-retarded fetuses and fetuses developing intrauterine distress, the umbilical artery blood velocity waveform usually changes in a progressive manner as below

Further assessment tools

Abnormal umbilical artery Doppler is an indication of further sonographic workup of the degree of uteroplacental insufficiency:


Ultrasound - obstetric
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Article Information

rID: 13860
System: Obstetrics
Section: Approach
Synonyms or Alternate Spellings:
  • Umbilical artery Doppler assessment
  • Umbilical arterial colour Doppler assessment

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    Case 1: normal UA Doppler trace
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    Case 2: normal UA Doppler trace
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    Case 3: abnormal (absent positive end diastolic flow)
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