What is a normal umbilical‑cord Doppler pulsatility index at 38 weeks gestation in a fetus without growth restriction?

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Normal Umbilical Cord Doppler at 38 Weeks

A normal umbilical artery Doppler pulsatility index (PI) at 38 weeks gestation is defined as a value below the 95th percentile for gestational age, with continuous forward flow throughout diastole. 1

Defining Normal Doppler Parameters

The umbilical artery Doppler is considered normal when:

  • The pulsatility index (PI), resistance index (RI), or systolic-to-diastolic (S/D) ratio falls below the 95th percentile for gestational age 1
  • Continuous forward end-diastolic flow is present throughout the cardiac cycle 1
  • There is no absent or reversed end-diastolic velocity (AEDV or REDV) 1

Technical Considerations for Measurement

  • Doppler waveforms can be obtained from any segment along the umbilical cord, though waveforms near the placental end show slightly higher end-diastolic velocities than those near the fetal insertion 1
  • This variation along the cord is minimal and does not significantly affect clinical decision-making 1
  • In fetuses with isolated two-vessel cord (single umbilical artery), PI values are significantly lower (mean 0.86 ± 0.19) compared to three-vessel cords (mean 1.02 ± 0.23), requiring different reference ranges 2

What Constitutes an Abnormal Doppler

An abnormal umbilical artery Doppler is defined as:

  • PI, RI, or S/D ratio greater than the 95th percentile for gestational age 1
  • Absent end-diastolic velocity (AEDV), indicating severe placental insufficiency 1
  • Reversed end-diastolic velocity (REDV), representing critical fetal compromise 1

Clinical Implications at 38 Weeks

For a fetus without growth restriction at 38 weeks:

  • Normal Doppler values indicate adequate placental function and low-resistance flow in the fetoplacental circulation 3
  • The gestational age-related decrease in PI values throughout pregnancy reflects progressive reduction in placental vascular resistance 3
  • If growth restriction is present with normal Doppler at 38 weeks, delivery is recommended at 38-39 weeks 4, 5

Important Caveats

  • Sampling both umbilical arteries rather than one may detect abnormalities in 57.7% of cases where only one artery is abnormal, potentially altering surveillance decisions 6
  • The mean discrepancy between paired umbilical artery PI values is 11.7%, and exceeds 20% in 15.8% of growth-restricted fetuses 6
  • Using the highest PI of the two arteries increases detection of abnormal values to 28.9% compared to 19.2% when averaging both arteries 6

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

3
Research

Doppler assessment of the fetoplacental circulation in normal and growth-retarded fetuses.

European journal of obstetrics, gynecology, and reproductive biology, 1984

4
Guideline

Management of Intrauterine Growth Restriction at 38 Weeks with Severe Oligohydramnios

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

5
Guideline

Timing of Delivery for Fetal Growth Restriction (FGR) with Abnormal Dopplers

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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