Adverse perinatal outcomes are strongly associated with degree of abnormality in uterine artery Doppler pulsatility index.

Objective: To investigate the association between varying degrees of abnormality in the Doppler uterine artery pulsatility index (UtA-PI) and adverse perinatal outcome.

Methods: This was a prospective study of women with a singleton, non-anomalous pregnancy in whom UtA-PI was measured universally in midpregnancy and who gave birth in Oxford University Hospitals, Oxford, UK, between 2016 and 2023. Relative risk ratios (RRR) for the primary outcomes of extended perinatal mortality and live birth with a severe small-for-gestational-age (SGA) neonate were calculated using multinomial logistic regression, for early preterm birth (before 34 + 0 weeks' gestation) and late preterm/term birth (at or after 34 + 0 weeks). Risks were also investigated for iatrogenic preterm birth and a composite adverse outcome before 34 + 0 weeks.

Results: Overall, 33 364 pregnancies were included in the analysis. Compared to those with a normal UtA-PI, the risk of extended perinatal mortality with delivery before 34 + 0 weeks was higher in women with UtA-PI ≥ 90^th percentile (RRR, 4.7 (95% CI, 2.7-8.0); P < 0.001), but this was not demonstrated in births at or after 34 + 0 weeks. The risk of live birth with severe SGA was associated strongly with abnormal UtA-PI for early births (RRR, 26.0 (95% CI, 11.6-58.2); P < 0.001) and later births (RRR, 2.3 (95% CI, 1.8-2.9); P < 0.001). Women with raised UtA-PI were more likely to have an early iatrogenic birth (RRR, 7.8 (95% CI, 5.5-11.2); P < 0.001). For each outcome before 34 + 0 weeks and the composite outcome, the risk increased significantly in association with the degree of abnormality in the UtA-PI (from < 90^th, 90-94^th, 95-98^th to ≥ 99^th percentile) (P_trend < 0.001). When using the 90^th percentile as opposed to the 95^th, there was a significant improvement in the overall predictive accuracy (as determined by the area under the receiver-operating-characteristics curve) for the composite adverse outcome (χ² = 6.64, P = 0.01) and iatrogenic preterm birth (χ² = 4.10, P = 0.04).

Conclusions: Elevated UtA-PI is a key predictor of iatrogenic preterm birth, severe SGA and perinatal loss up to 34 + 0 weeks' gestation. The 90^th percentile for UtA-PI should be used, and management should be tailored according to the degree of abnormality, as pregnancies with very raised UtA-PI measurement constitute a group at extreme risk of adverse outcome. © 2024 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.