Purpose: To determine reference values for umbilical Doppler pulsatility index in fetuses with isolated two-vessel cord and to compare these values with standard umbilical Doppler pulsatility index curves from 23 to 40 gestational weeks.
Methods: A retrospective longitudinal cohort study was conducted between January 2014 and December 2017 in a tertiary referral hospital and included 62 pregnant women with isolated single umbilical artery (two-vessel cord) and 174 measurements. Only uncomplicated term pregnancies were included. A reference curve for umbilical Doppler pulsatility index was built up and compared with a standard curve commonly used for fetuses with three-vessel cord.
Results: Umbilical Doppler pulsatility index values were much lower than expected in cases with two-vessel cord compared to 3-vessel cord: mean of the regression equations was 1.02 ± 0.23 vs. 0.86 ± 0.19, respectively (p value < 0.001). This difference was quite constant across the gestational weeks considered, showing that the slopes of the two regressions were very similar.
Conclusion: Reference curves for umbilical Doppler pulsatility index in two-vessel cord pregnancies were determined. Pulsatility index values were significantly different compared with those commonly used for three-vessel cord. Using lower reference values for umbilical pulsatility index in cases with two-vessel cord may allow a better identification of fetuses affected with intrauterine growth restriction, thus improving fetal surveillance.
Keywords: Linear regressions comparison; Reference curve; Single umbilical artery; Two-vessel cord; Umbilical pulsatility index.