What does a pulsatility index (PI) of 2.235 on a fetal doppler scan in the first trimester indicate for fetal development and what are the recommended next steps?

First Trimester Uterine Artery Doppler PI 2.235: Interpretation and Management

A uterine artery pulsatility index of 2.235 in the first trimester indicates elevated placental vascular resistance and identifies this pregnancy as high-risk for developing fetal growth restriction (FGR) and early-onset preeclampsia, warranting initiation of low-dose aspirin prophylaxis before 16 weeks and enhanced surveillance throughout pregnancy.

Understanding the Clinical Significance

What This PI Value Means

• Elevated placental impedance: A PI of 2.235 in the first trimester reflects abnormal trophoblastic invasion of maternal spiral arterioles, which normally should decrease impedance progressively with advancing gestational age 1.

• Risk stratification tool: In high-risk women assessed at 19-24 weeks, abnormal uterine artery Doppler can identify 90% of FGR cases delivering before 32 weeks with a 10% false-positive rate 2.

• Maternal-side assessment: Uterine artery Doppler assesses the maternal side of placental flow, indicating inadequate maternal adaptation to pregnancy rather than direct fetal compromise 2.

Critical Limitation to Understand

• Not for ongoing management: The American College of Obstetricians and Gynecologists explicitly states that uterine artery PI Doppler should not be used for routine clinical management of FGR or preeclampsia, as it does not add clinically valuable information beyond umbilical artery Doppler for guiding delivery timing or improving outcomes 2.

• Screening versus surveillance distinction: This measurement serves as a one-time risk assessment tool, not a parameter for serial monitoring or delivery decisions 2.

Immediate Management Steps

Aspirin Prophylaxis (Most Critical Intervention)

• Start low-dose aspirin immediately: Five of six international guidelines (83%) recommend low-dose aspirin for prevention of small-for-gestational-age (SGA) infants, with three specifying initiation by 16 weeks 1.

• Specific dosing: Administer 75-160 mg daily, taken in the evening to maximize efficacy based on randomized controlled trial evidence 1.

• Timing is essential: Aspirin must be started before 16 weeks (ideally) or no later than 20 weeks to provide benefit 1.

Risk Factor Assessment

• Comprehensive evaluation: Assess for additional risk factors including prior preeclampsia, prior FGR, chronic hypertension, renal disease, diabetes, antiphospholipid syndrome, and smoking 1.

• Smoking cessation: If applicable, initiate smoking cessation counseling immediately, as this is a modifiable risk factor 1.

Surveillance Protocol Throughout Pregnancy

Serial Growth Monitoring

• Fundal height measurements: Implement serial fundal height measurements on a customized chart starting at 22-26 weeks, with ultrasound if measurements fall below the 10th centile or show static/slow growth 1.

• Ultrasound biometry: Schedule growth ultrasounds every 3-4 weeks starting in the second trimester to detect FGR early 1.

When to Initiate Umbilical Artery Doppler

• Once FGR is suspected: If estimated fetal weight (EFW) falls below the 10th percentile, immediately initiate umbilical artery Doppler surveillance, as this is the primary vessel with Level I evidence for reducing perinatal mortality 3, 4.

• Umbilical artery is the key parameter: The American College of Obstetricians and Gynecologists recommends umbilical artery Doppler as the primary vessel to observe in FGR, not continued uterine artery assessment 3.

Doppler Surveillance Algorithm (If FGR Develops)

Normal umbilical artery Doppler:

• Weekly Doppler assessment 3
• Continue until 37 weeks, then deliver 3

Decreased end-diastolic flow (but forward flow present):

• Weekly umbilical artery Doppler 3
• Delivery at 37 weeks 3

Absent end-diastolic velocity (AEDV):

• Doppler assessment 2-3 times per week 3
• Administer antenatal corticosteroids 3
• Delivery at 33-34 weeks 3

Reversed end-diastolic velocity (REDV):

• Hospitalization required 3
• Cardiotocography monitoring 1-2 times daily 3
• Administer antenatal corticosteroids 3
• Delivery at 30-32 weeks 3

Common Pitfalls to Avoid

Do Not Repeat Uterine Artery Doppler for Management

• Single assessment only: Uterine artery Doppler is for initial risk stratification, not serial surveillance 2.

• Switch to umbilical artery: Once FGR is diagnosed, umbilical artery Doppler becomes the primary surveillance tool with Level I evidence for reducing perinatal mortality (RR 0.71; 95% CI, 0.52-0.98) 3.

Do Not Delay Aspirin Initiation

• Time-sensitive intervention: The window for aspirin efficacy closes after 20 weeks, making immediate initiation critical 1.

• Evening dosing matters: Administer aspirin in the evening rather than morning to maximize efficacy 1.

Do Not Assume Normal Growth Excludes Risk

• Late-onset FGR can occur: Even with normal early growth, 15-20% of late-onset growth-restricted fetuses with normal umbilical artery Doppler show cerebral vasodilation, indicating compromise 4.

• Maintain vigilance: Continue serial fundal height measurements and growth ultrasounds throughout pregnancy 1.

Preeclampsia Surveillance

• Comprehensive assessment at diagnosis: If preeclampsia develops, perform fetal biometry, amniotic fluid volume, and both uterine and umbilical artery Doppler as a one-time comprehensive assessment to characterize placental dysfunction severity 2.

• Ongoing surveillance shifts to umbilical artery: After initial assessment, serial umbilical artery Doppler every 1-2 weeks guides subsequent management 2, 3.