Application of ultrasonic transit time flowmetry to the measurement of umbilical vein blood flow at caesarean section.

Abstract

To determine the applicability of ultrasonic transit time flowmetry to the measurement at caesarean section of umbilical vein blood flow rate and to examine the relationship between flow rates and birthweight for gestational age. Umbilical vein blood flow was measured at caesarean section using a transonic time flow probe on a loop of the umbilical cord in 33 appropriate and 21 small for gestational age fetuses. The mean (SD) umbilical vein blood flow in the 54 fetuses was 78.4 (23.1) ml kg-1 min-1. There was a linear relation between umbilical vein blood flow measured by ultrasonic transit time flowmetry and birthweight (r = 0.63, P < 0.0001). The mean umbilical vein blood flow in appropriate for gestational age fetuses [90 (18) ml kg-1 min-1] was greater than that in the small for gestational age group [66 (23) ml kg-1 min-1], P < 0.04). Umbilical vein blood flow measurements obtained by the ultrasonic transit time flowmetry technique are simple to perform and compare well with reported values obtained by the Doppler ultrasound technique (when vessel diameter is greater than 4 mm). Umbilical venous blood flow rate is significantly lower in small for gestational age fetuses.