Abnormal umbilical artery pulsatility index in appropriately grown fetuses in the early third trimester: an observational cohort study

Abstract

Objective The aim of this study was to determine if appropriately grown fetuses (those that are not small-for-gestational-age) with a raised umbilical artery pulsatility index (>95th centile) in the early third trimester are at increased risk of placental dysfunction and adverse outcome. Methods This is a 5-year retrospective cohort study using routinely collected data. Inclusion criteria were singleton, non-anomalous pregnancies having a growth scan with umbilical artery Doppler velocimetry between 28 + 0 and 33 + 6 weeks’ gestation. Small-for-gestational-age fetuses were excluded. Cases were classified as group 1 (those with an umbilical artery pulsatility index >95th centile at any scan during target window) or group 2 (those where the umbilical artery pulsatility index was ≤95th centile at all scans). p-Values and odds ratios were calculated. Logistic regression was used to compute odds ratios adjusted for baseline estimated weight z-score, gestational age at delivery, and labor induction. Results After exclusions, there were 202 pregnancies in group 1 and 7950 in group 2. Differences in baseline characteristics between the groups include age (median age was 30 for group 1 and 32 for group 2, p < .001), smoking (group 1 were more likely to smoke, p < .001) and labor induction (more common in group 1, p = .03). Among those delivering ≥34 + 0, group 1 were more likely to be small-for-gestational-age and have an abnormal cerebro-placental ratio at the final scan (OR 6.76, CI 4.23–10.80 and OR 5.07, CI 3.37–7.63 respectively), and to develop features of growth restriction (OR 9.85, CI 6.27–15.49). Group 1 were also more likely to deliver <37 + 0 weeks’ gestation (OR 1.71, CI 1.13–2.58) and to have birthweight <10th or <3rd centile (OR 5.26, CI 3.65–7.58 and OR 6.13, CI 3.00–12.54 respectively). These associations remained significant when adjusted for estimated weight at the initial scan. Conclusions These data suggest that raised umbilical artery pulsatility index in an appropriately grown fetus at 28 + 0 to 33 + 6 weeks’ gestation is associated with subsequent development of growth restriction markers and an increased risk of moderate and severe small-for-gestational-age at birth. This is independent of the estimated weight of these babies at the index scan.