Acute increase of umbilical artery vascular flow resistance in compromised fetuses provoked by uterine contractions

Abstract

Background: An impaired placental circulation is involved in the mechanism of late fetal heart rate (FHR) decelerations. Objectives: To explore umbilical artery (UA) Doppler velocimetry changes in response to uterine contractions during the oxytocin challenge test (OCT) and assess the potentially clinical value of ‘OCT Doppler velocimetry’. Methods: 111 women with pregnancy complications were subjected to an OCT with simultaneous recordings of FHR and UA pulsatility index (PI). Positive OCT cases (late FHR decelarations) were compared with negative OCT cases (normal FHR patterns). Only negative OCT cases were allowed a trial of vaginal delivery. Results: The UA PI was higher in OCT positive ( N=21) than in negative cases ( N=90) during uterine contractions and relaxations ( P<0.05), but not during basal measurements. A positive OCT, but not negative, was associated with an increase of PI during contractions and relaxations compared with basal measurements ( P<0.05). Fetal growth restriction ( N=58), operative delivery for fetal distress (ODFD) in labor ( N=10), and birth asphyxia ( N=8) were not associated with PI changes significantly different from cases without these complications. Conclusions: During uterine contractions and relaxations, but not during basal measurements, a significantly higher UA PI evolved in OCT positive cases compared with OCT negative cases. This indicates a pathophysiological mechanism disclosed only during uterine activity. Although these changes would not have been revealed by traditional Doppler velocimetry, the data suggest a limited predictive value of ‘OCT Doppler velocimetry’ on the short-term neonatal outcome.