Umbilical venous flow rate in term fetuses: can variations in flow predict intrapartum compromise?

The objective of the study was to investigate the distribution of umbilical venous flow rates, measured in early labor, in a cohort of normal term pregnancies and to establish the relationship between umbilical venous flow and subsequent intrapartum outcome.

Five hundred eighty-nine women with uncomplicated, term, singleton pregnancies were recruited to this prospective observational study prior to active labor (dilation of 4 cm or less) at Queen Charlotte's and Chelsea Hospital (London, UK). All participants underwent an ultrasound examination, during which fetal biometry, umbilical venous flow velocity, and umbilical vein diameter were recorded. Umbilical venous flow rate was then calculated. Following delivery, intrapartum and neonatal outcomes were correlated with the ultrasound findings. Cases were subdivided according to mode of delivery, and mean umbilical venous flow rates were compared between the groups. Cases were also subdivided according to umbilical venous flow rate (less than the 20th centile, 20th-80th centile, and greater than the 80th centile), and the incidence of diagnoses of fetal compromise was compared.

Fetuses delivered by emergency cesarean for presumed fetal compromise had the lowest umbilical venous flow rates (both corrected for and uncorrected for birthweight) (P = .02 and P = .001, respectively). Fetuses with the lowest umbilical venous flow rates were significantly more likely to require emergency cesarean for presumed fetal compromise than those with the highest flow rates (15.7% vs 5.6%, relative risk, 2.83; 95% confidence interval, 1.16-6.91).

Fetuses with the lowest umbilical venous flow rates are at increased risk of a subsequent diagnosis of intrapartum fetal compromise. Measurement of umbilical venous flow could contribute to the risk stratification of pregnancies prior to labor.