Doppler measurements of the intraabdominal part of the umbilical arteries in normal pregnancies

Background: In the management of high risk pregnancies, blood flow measurements in the umbilical arteries (Aa. umb) have reduced perinatal morbidity and mortality. No consensus has been reached about the optimal location of measurements along the umbilical cord. The present study analyses the blood flow in both umbilical arteries where they pass by the fetal bladder. Patients and methods: In 48 normal pregnancies, Doppler examinations were used to measure the pulsatility indices (PI). From the 20th week of pregnancy onward, the PI were measured once every four weeks in the intraabdominal segments of the right and the left Aa. umb. lateral to the fetal bladder. Measurements were also done in a free loop and at the placental insertion. Results: For all locations, normal ranges were calculated. The PI at all four sites decreased as the pregnancies were approaching term. In the III. trimester, the standard deviations of PI were smaller than in the II. trimester. The PI at the intraabdominal segment of the right and the left umbilical arteries turned out to be similar to each other and exceeded the values measured at the free loop and at the placental insertion respectively. Conclusion: The intraabdominal segments of the umbilical arteries were defined as a new location for PI measurements. When adopting a fixed place of measurement, it is likely that the reproducibility of PI measurements will be increased. Discussion: The higher PI at the intraabdominal segment of the umbilical arteries are caused by the more central location compared to the placental insertion.