Do heart rate and velocity variability derived from umbilical artery velocity waveforms change prior to clinical pregnancy-induced hypertension?

OBJECTIVE To investigate the hypothesis that alterations in heart rate variability, peak systolic velocity variability and time-averaged velocity variability in the human umbilical artery may predict early signs of dysfunctional fetal-placental coupling in pregnancies that later develop pregnancy-induced hypertension. METHODS Doppler flow velocity recordings from the umbilical artery were performed at 10-20 weeks of gestation in 12 nulliparous women who subsequently developed pregnancy-induced hypertension. From umbilical artery velocity waveforms of at least 12 s in duration we determined absolute values and beat-to-beat variability in fetal heart rate, peak systolic and time-averaged velocity and compared these findings with those in normal nulliparous pregnant women matched for gestational age. RESULTS Absolute values for fetal heart rate, peak systolic and time-averaged velocity as well as beat-to-beat variability in fetal heart rate did not differ significantly between women later developing pregnancy-induced hypertension and normal controls. However, variability in peak systolic velocity and time-averaged velocity were decreased in women who subsequently developed pregnancy-induced hypertension. CONCLUSIONS Whereas fetal heart rate variability was similar, umbilical artery flow velocity variability was reduced in women developing pregnancy-induced hypertension compared with controls. It is proposed from this study that variability of the umbilical artery flow velocity is associated with mechanical changes in the vascular bed of women who later develop pregnancy-induced hypertension.