The left portal vein as an indicator of watershed in the fetal circulation: development during the second half of pregnancy and a suggested method of evaluation.
OBJECTIVE
The left portal vein represents a watershed area in the fetal circulation and the change of flow direction is a suggested marker of circulatory compromise. Our aim was to study the left portal vein of uncompromised human pregnancies and establish reference ranges.


METHODS
One hundred and sixty low-risk pregnant women were recruited to a longitudinal study that included four to five Doppler measurements at monthly intervals during the second half of pregnancy.


RESULTS
Based on 554 Doppler recordings we found time-averaged maximum flow velocities increasing from a mean of 10.6 cm/s to 14.2 cm/s during 21-31 weeks of gestation, remaining stable until 37 weeks and decreasing towards term. Intermittent flow reversal occurred during fetal respiratory movements, and continuous flow reversal was seen in 2/160 fetuses close to delivery.


CONCLUSIONS
We propose time-averaged maximum blood velocity measurement for quantification of the watershed phenomenon in the left portal branch, and have provided reference ranges for single observations and serial measurements.
Kessler
J
J
Department of Clinical Medicine, Section for Obstetrics and Gynecology, University of Bergen, University of Bergen and the Norwegian Institute of Public Health, Bergen, Norway.
Rasmussen
S
S
Kiserud
T
T
D000328:Adult; D001783:Blood Flow Velocity; D005069:Evaluation Studies as Topic; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008137:Longitudinal Studies; D010547:Persistent Fetal Circulation Syndrome / Q000000981:diagnostic imaging*; D011169:Portal Vein / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011256:Pregnancy Outcome; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D014463:Ultrasonography