Uterine artery Doppler in early labor and perinatal outcome of low-risk term pregnancies: prospective multicenter study.

OBJECTIVE: The prediction of adverse perinatal outcomes in low-risk pregnancies is poor, mainly due to the lack of reliable biomarkers. Uterine artery Doppler is closely associated with placental function and could assist in the peripartum detection of subclinical placental insufficiency. The objective of this study was to evaluate the relationship between mean uterine artery pulsatility index (PI) measured in early labor with obstetric intervention for suspected intrapartum fetal compromise and adverse perinatal outcomes in uncomplicated singleton term pregnancies.

METHODS: This was a prospective multicenter observational study conducted across four tertiary Maternity Units. Low-risk term pregnancies with spontaneous onset of labor were included. The mean uterine artery PI was recorded in between uterine contractions in women admitted for early labor and converted into multiples of the median (MoM). The primary outcome of the study was the occurrence of obstetric intervention - i.e., cesarean section or instrumental delivery - due to suspected intrapartum fetal compromise. The secondary outcome was represented by the occurrence of composite adverse perinatal outcome, defined as one of the following: acidemia (umbilical artery pH<7.10 and/or base excess >12) at birth and/or 5-min Apgar score < 7 and/or neonatal intensive care unit (NICU) admission.

RESULTS: Overall, 804 women were included, of whom 40 (5%) had a mean uterine artery PI MoM ≥95th percentile. Women who had an obstetric intervention for suspected intrapartum fetal compromise were more frequently nulliparous (72.2% vs 53.6%, P=0.008), had a higher frequency of mean uterine artery PI MoM ≥95th percentile (13.0% vs 4.4%, P=0.005), and had a longer duration of labor (456±221 vs 371±192 minutes, p=0.01). Logistic regression only retained as independently associated with obstetric intervention for suspected intrapartum fetal compromise mean uterine artery PI MoM ≥95th percentile (adjusted odds ratio (aOR), 3.48 (95% CI, 1.43-8.47), P=0.006) and multiparity (aOR, 0.45 (95% CI, 0.24-0.86), P=0.015). Mean uterine artery PI MoM ≥95th percentile was associated with a 0.13 (95% CI, 0.05-0.25) sensitivity, 0.96 (95% CI, 0.94-0.97) specificity, 0.18 (95% CI, 0.07-0.33) positive predictive value, 0.94 (95% CI, 0.92-0.95) negative predictive value, 2.95 (95% CI, 1.37-6.35) positive likelihood ratio and 1.10 (95% CI, 0.99-1.22) negative likelihood ratio for obstetric intervention for suspected intrapartum fetal compromise. Pregnancies with mean uterine artery PI MoM ≥ 95th percentile also showed a higher incidence of birthweight <10th percentile (20% vs 6.7%, P=0.002), NICU admission (7.5% vs 1.2%, P=0.001) and composite adverse perinatal outcome (15.0% vs 5.1%, P=0.008).

CONCLUSION: Our study conducted on a cohort of low-risk term pregnancies enrolled in early spontaneous labor shows an independent association between increased mean uterine artery PI and obstetric intervention for suspected intrapartum fetal compromise, albeit with moderate capacity to rule in and poor capacity to rule out this condition. This article is protected by copyright. All rights reserved.