Fetal umbilical artery flow velocity waveforms and placental resistance: pathological correlation

Abstract

Placental microvascular anatomy was correlated with antenatal assessment of the umbilical circulation in 106 patients to further validate the measurement of the A/B ratio (the ratio of peak systolic to least diastolic flow velocity) of the umbilical artery flow velocity time waveforms as an index of' blood flow resistance. Three groups of patients were studied: a normal group of 38 uncomplicated pregnancies, a control group of 33 potentially 'at risk' pregnancies with a normal A/B ratio matched by risk factors and gestation with the third group of 35 pregnancies with a high A/B ratio. Placental arterial resistance was quantitated by counting the number of small muscular arteries ((90ym diameter) in the tertiary stem villi in a standard microscopic field (mean 18.5 fielddplacenta). The modal small arterial vessel count was shown to be significantly less in the group with a high fetal risk and a high A/B ratio (1-2 arteriedfield) than in both the normal and control groups (7-8 arteriedfield). The tertiary villus count did not vary between groups. Antenatal studies of umbilical artery flow velocity waveforms with Doppler ultrasound identify a specific microvascular lesion in the placenta characterized by obliteration of small muscular arteries in the tertiary stem villi.

Assessment of Doppler velocimetry versus nonstress test in antepartum surveillance of high risk pregnancy

“…6 Once 60-70% of the vasculature is affected, absent or reversed end diastolic flow results. 7 Reversed end diastolic flow is an ominous finding and is associated with a high mortality rate within 1-7 days if fetus is left in utero.…”

Placental Defects in α7 Integrin Null Mice

“…Placental dysfunction can result in insufficient fetal nutrition, which can lead to intrauterine growth restriction (IUGR) [2][3][4][5][6]. At least 8% of human pregnancies end in infant death due to complications that arise from IUGR [1;7;8].…”

Doppler ultrasound in the assessment of suspected intra-uterine growth restriction

“…Pathological studies have demonstrated that increased impedance in the umbilical arteries becomes evident only when at least 60% of the placental vascular bed is obliterated (12) . Clinical studies of umbilical arterial flow velocity waveforms in intrauterine growth restriction have reported progressive increase in impedance to flow until absence and, in extreme cases, reversal of end-diastolic frequencies (13) .…”