What is the significance of a uterine Pulsatility Index (PI) Doppler scan in a pregnant individual with a history of previous pregnancy complications, chronic hypertension, or placental insufficiency?

Uterine Artery Pulsatility Index Doppler in High-Risk Pregnancy

Uterine artery PI Doppler should not be used for routine clinical management of fetal growth restriction (FGR) or preeclampsia, as it does not add clinically valuable information beyond umbilical artery Doppler for guiding delivery timing or improving outcomes. 1

Primary Role: Risk Stratification, Not Management

Screening Context (Not Recommended for Routine Use)

• Uterine artery Doppler is not recommended as a screening tool for identifying pregnancies that will develop FGR because of inconsistent evidence of benefit and lack of standardization for technique, gestational age, and abnormality criteria 1

• In high-risk women at 19-24 weeks, abnormal uterine artery Doppler (PI >95th percentile or notching) can identify 90% of FGR cases delivering before 32 weeks with a 10% false-positive rate, but this does not translate to improved clinical management 2

• The test performs better in high-risk populations: an elevated RI (≥0.58 or ≥90th percentile) in the second trimester has a positive likelihood ratio of 10.9 for severe FGR, with a negative likelihood ratio of 0.20 1

What Abnormal Findings Mean

• Abnormal uterine artery Doppler reflects failed trophoblastic invasion of the myometrial spiral arteries, resulting in reduced uteroplacental perfusion and high-impedance maternal placental circulation 1, 3

• An elevated PI (>95th percentile) or persistent diastolic notching indicates increased risk for preeclampsia (relative risk 7.3), FGR (relative risk 3.9), and overall placental insufficiency (relative risk 4.5) 4

• When combined with umbilical artery Doppler, uterine artery assessment offers better prediction of adverse perinatal outcomes than either measure alone, but this does not improve clinical management 1

Why It's Not Used for Management

Umbilical Artery Doppler is Superior

• Umbilical artery Doppler is the preferred vessel for guiding management in FGR, as it significantly reduces perinatal deaths (RR 0.71), cesarean deliveries (RR 0.90), and inductions of labor (RR 0.89) 1, 5

• Once FGR is diagnosed, serial umbilical artery Doppler every 1-2 weeks (or more frequently with abnormalities) directly guides delivery timing based on fetal compromise 1

• Uterine artery Doppler assesses the maternal side of placental flow, while umbilical artery Doppler assesses the fetal side—the latter is what determines fetal well-being and delivery timing 1

Limited Diagnostic Accuracy

• Despite strong associations with adverse outcomes, uterine artery Doppler has limited diagnostic accuracy and clinical utility in predicting FGR, small-for-gestational-age birth, and perinatal mortality 1

• The sensitivity for detecting FGR is low (12% in first trimester), and even second-trimester screening shows wide variation in performance across studies 1

When Uterine Artery Doppler May Be Considered

Preeclampsia Surveillance

• At initial diagnosis of preeclampsia, fetal biometry, amniotic fluid volume, and both uterine and umbilical artery Doppler should be performed as part of comprehensive assessment 1

• This is a one-time assessment to characterize placental dysfunction severity, not ongoing surveillance 1

Research and Risk Prediction Models

• First- and second-trimester prediction models combining maternal factors, biochemical markers (PAPP-A, PlGF, sFlt-1), and uterine artery Doppler can achieve >90% detection rates for early-onset preeclampsia and FGR 1, 6

• However, these models lack external validation and have not demonstrated improved pregnancy outcomes, limiting clinical applicability 1

• A mean PI cutoff of 2.27 at 11-14 weeks shows 92.9% sensitivity and 97.1% specificity for preeclampsia prediction, but this remains investigational 6

Common Pitfalls to Avoid

• Do not use uterine artery Doppler to guide delivery timing in FGR—umbilical artery Doppler, cardiotocography, and biophysical profile are the appropriate tools 1, 2

• Do not delay umbilical artery Doppler surveillance while waiting for uterine artery results, as umbilical artery assessment reduces perinatal death by 38% when incorporated into management 2

• Do not rely on uterine artery Doppler alone for risk stratification—it performs best when combined with maternal history and biochemical markers, but even then does not change management 1, 7

• Avoid performing uterine artery Doppler in low-risk populations for screening, as it does not confer benefit and is not cost-effective 1, 2

Practical Algorithm for High-Risk Pregnancy

1. At 19-24 weeks in high-risk women (prior preeclampsia, chronic hypertension, placental insufficiency history): Consider uterine artery Doppler for risk stratification only 2

2. If abnormal (PI >95th percentile or notching): Increase surveillance frequency with serial growth scans every 2-4 weeks and plan for umbilical artery Doppler initiation at 26-28 weeks 2, 5

3. Once FGR is diagnosed: Switch to umbilical artery Doppler as primary surveillance tool every 1-2 weeks, with uterine artery Doppler providing no additional management value 1, 2

4. If preeclampsia develops: Perform comprehensive assessment including uterine artery Doppler once at diagnosis, then follow with serial umbilical artery Doppler and other fetal well-being tests 1