DISPARATE BLOOD-FLOW PATTERNS IN PARALLEL UMBILICAL ARTERIES

Objective: To compare resistance to blood flow between two umbilical a rteries at the same cord site during the second half of pregnancy. Met hods: We evaluated 80 patients with singleton pregnancies cross-sectio nally at gestational ages ranging from 20-40 weeks' gestation. Resista nce to blood flow was measured separately by means of systolic-diastol ic ratio (S/D) for both umbilical arteries of each subject at the same site of transverse cord section. The higher mean Value of the one umb ilical artery was designated S/D-max, whereas the lower mean value of the other paired umbilical artery was designated S/D-min. The percent difference between the two values was calculated for each pair of meas urements. Then these data were stratified by gestational age.Results: The overall mean (+/- standard deviation [SD]) S/D-max was significant ly different from S/D-min (2.62 +/- 0.58 versus 2.27 +/- 0.40, respect ively P < .001). The mean (+/- SD) calculated percent difference of 14 .9 +/- 10.4% ranged in a downward trend over the course of late pregna ncy from 29.2 +/- 17.1% in the 20-28 weeks' gestational age group to 1 0.4 +/- 6.1% among those at term (37-40 weeks); the slope of this tren d was -1.32 +/- 8.55% per week, a statistically significant trend (P < .001). There was a more than 20% difference in more than one quarter (29%) of the 80 pairs of umbilical arteries we studied. Cases with the se large differences were concentrated mostly among those with earlier gestational ages: At term, only 8.6% showed this difference in now re sistance measurements. Conclusion: The resistance to blood flow in one umbilical artery often differs considerably from that in the other. T he difference, which equalizes gradually as pregnancy advances, perhap s as a result of functional maturation of the Hyrtl anastomosis betwee n the vessels, may have clinical importance for identification and eva luation of the potentially jeopardized fetuses, either as an early mar ker of fetal hypoxia or in interpretating fetal status. (C) 1998 by Th e American College of Obstetricians and Gynecologists.