UMBILICAL ARTERY BLOOD FLOW

Umbilical artery waveform	Umbilical Vein Waveform

• Normal umbilical artery.
• Indices are lower at the placental than the fetal end (1). The difference is minimal and therefore it is probably not important to obtain waveforms always at the exact same level.
• <20 weeks GA
• Placental flow is in a high resistance bed and the value of umbilical artery velocimetry is limited (2).
• End diastolic flow is often absent (2).
• >20 weeks GA
• Progressive increase in diastolic flow velocities resulting in a progressive decrease in measured indices (3,4).
• A low resistance pattern with high forward flow velocities in both the systolic and diastolic component of the cardiac cycle.
• The PI, RI and S/D ratio all decrease with advancing gestation, probably due to a decrease in placental vascular resistance (3,4). Throughout pregnancy the overall increase in placental size as well as the associated increase in the number of villi result in a continuing expansion of the placental vascular tree, and therefore a decreasing vascular resistance. The feto-placental circulation acts as a low resistance unit, resulting in continuous blood flow in the umbilical artery throughout the cardiac cycle.

• Graph Of Umbilical Artery Pulsatility Index
• Umbilical artery to middle cerebral artery ratio (Table)–Arduini et.al. 1992
• Umbilical artery to middle cerebral artery ratio (Graph)–Arduini et.al. 1992

Effect of fetal breathing on the doppler waveform in the umbilical artery and vein.
Effect of hiccups on the doppler waveform in the umbilical artery

REFERENCES

1. Maulik D, Yarlagadda AP, Youngblood JP et.al. Components of variability of umbilical artery doppler velocimetry: A prospective analysis. Am J Obstet Gynecol 1989;6:1406-1412.
2. Wladimiroff JW, Huisman TWA, Stewart PA. Fetal and umbilical flow velocity waveforms between 10-16 weeks gestation. A preliminary study. Obstet Gynecol 1991;78:812-814.
3. Trudinger BJ, Stevens D, Connelly A et.al. Umbilical artery flow velocity waveforms and placental resistance: The effect of embolization of the umbilical circulation. Am J Obstet Gynecol 1987;157:1443-1449.
4. Trudinger BJ, Giles WB, Cook CM et.al. Fetal umbilical artery flow velocity waveforms and placental resistance: Clinical significance. Br J Obstet Gynaecol 1985;92:23-30.