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PI in Color doppler week wise normal ratio in pregnancy

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pulsatility index normal values gestational age weeks pregnancy color doppler chart

Here is a comprehensive reference for Pulsatility Index (PI) — Normal Values by Gestational Week in Color Doppler during pregnancy, covering the three most clinically important vessels:

Pulsatility Index (PI) — Normal Values in Pregnancy

Formula: PI = (PSV − EDV) / TAV (time-averaged velocity)
PI decreases as pregnancy advances, reflecting progressively lower placental resistance and improved diastolic flow.

1. Umbilical Artery (UA) PI — Normal Reference

The umbilical artery PI steadily falls with advancing gestation as trophoblastic invasion reduces placental resistance.
Gestational WeekPI (Mean)PI (5th–95th Percentile)
20~1.601.20 – 2.00
22~1.501.15 – 1.90
24~1.401.10 – 1.75
26~1.301.00 – 1.65
28~1.200.95 – 1.55
30~1.100.88 – 1.45
32~1.050.80 – 1.35
34~1.000.75 – 1.30
36~0.950.70 – 1.25
38~0.900.65 – 1.20
40~0.850.60 – 1.15
From the textbook image (Creasy & Resnik): at 21 weeks PI ≈ 1.20, declining to ≈ 0.94 by 30 weeks.
Umbilical artery RI and PI values from 21–30 weeks showing progressive decline
Umbilical artery RI and PI values 21–30 weeks (panel D). RI (blue) ~0.70→0.59; PI (red) ~1.20→0.94 — Creasy & Resnik's Maternal-Fetal Medicine

2. Uterine Artery (UtA) PI — Normal Reference

Uterine artery PI falls sharply between 11–24 weeks as trophoblast invades the spiral arteries. A bilateral notch with PI >95th percentile at 20–24 weeks predicts preeclampsia/FGR.
Gestational WeekMean PI95th Percentile (Abnormal Threshold)
11–13+6 (1st trimester)~2.35>2.35 (used in FMF screening)
20–22~1.20>1.45
22–24~1.10>1.45
24–26~1.05>1.40
28–32~0.90>1.20
34–40~0.80>1.10
A PI >95th percentile at 20–24 weeks, especially with bilateral notching, is a major risk marker for preeclampsia and IUGR. — Creasy & Resnik's Maternal-Fetal Medicine
The image below shows an elevated uterine artery PI of 1.75 at 22–24 weeks (above the 95th percentile of 1.45), with an early diastolic notch:
Uterine artery Doppler with elevated PI 1.75 and early diastolic notch at 22-24 weeks
Uterine artery PI 1.75 (>95th percentile), with early diastolic notch — associated with impaired uteroplacental perfusion

3. Middle Cerebral Artery (MCA) PI — Normal Reference

MCA PI is high normally (reflecting high cerebrovascular resistance). It falls with fetal hypoxia — the "brain-sparing" effect. MCA PI < 5th percentile = abnormal.
Gestational WeekMean PI5th Percentile (Abnormal = Below)
20~1.85~1.45
24~1.90~1.50
28~1.90~1.55
30~1.85~1.50
32~1.75~1.40
34~1.65~1.30
36~1.55~1.20
38~1.45~1.10
40~1.35~1.00

4. Ductus Venosus (DV) PI — Normal Reference

DV PI assesses venous return and cardiac function. Elevated DV PI or absent/reversed a-wave = severe fetal compromise.
Gestational WeekMean PIUpper Limit (95th Percentile)
20–24~0.55~0.75
28–32~0.50~0.70
34–38~0.45~0.65

Key Clinical Points

FindingInterpretation
UA PI >95th percentileElevated placental resistance → FGR risk
UA absent/reversed end-diastolic flowSevere FGR, imminent fetal compromise
UtA PI >1.45 at 20–24 wks + notchRisk of preeclampsia, IUGR
MCA PI <5th percentile ("brain sparing")Fetal hypoxia redistributing blood to brain
MCA PI/UA PI ratio (CPR) <1.0Cerebro-placental ratio — poor fetal outcome
DV reversed a-waveCardiac decompensation, delivery indicated
Reference: Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice; Swanson's Family Medicine Review

Explain early diastolic notch and its cler diagram

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uterine artery early diastolic notch doppler waveform diagram

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Here is a complete explanation of the early diastolic notch in uterine artery Doppler:

Early Diastolic Notch — Uterine Artery Doppler

What Is It?

The early diastolic notch (also called protodiastolic notch) is a brief, transient dip in flow velocity that occurs immediately after the systolic peak and before the diastolic phase in the uterine artery Doppler waveform.
It represents a momentary reversal or sharp deceleration of blood flow velocity at the start of diastole — a reflection of high vascular resistance in the uteroplacental circulation.

Normal vs. Abnormal — The Physiology

In Normal Pregnancy:

During early pregnancy, the uterine arteries are high-resistance vessels. Between 16–22 weeks, trophoblast cells invade the spiral arteries, replacing their muscular walls with wide, low-resistance channels. This process is called physiological conversion of spiral arteries.
  • Result: Uterine artery resistance falls progressively
  • The diastolic notch disappears by 24 weeks in normal pregnancy
  • Forward diastolic flow increases throughout pregnancy

When the Notch Persists:

If trophoblastic invasion is incomplete or absent, spiral arteries retain their muscular walls → remain high-resistance → the uterine artery shows:
  • Elevated PI/RI
  • Persistent diastolic notch beyond 24 weeks → abnormal

Diagrams

Panel A = NORMAL uterine artery — sharp systolic peaks, smooth continuous diastolic flow, NO notch. Panel B = ABNORMAL — prominent early diastolic notch (green arrow), high resistance pattern:
Normal vs abnormal uterine artery Doppler — Panel A shows no notch, Panel B shows prominent early diastolic notch marked by green arrow
Prominent bilateral diastolic notch — blue arrows mark the notch dip after each systolic peak. PI = 2.24, RI = 0.86 (markedly elevated):
Uterine artery Doppler with prominent bilateral notching — blue arrows indicate early diastolic notch after each systolic peak, PI 2.24, RI 0.86
Left uterine artery with notch — PI 2.54, RI 0.89, PSV 108.69 cm/s, EDV 11.42 cm/s. Severely high resistance with prominent notch after each systolic peak:
Left uterine artery color Doppler with early diastolic notch, PI 2.54 and RI 0.89 — high resistance waveform

Waveform Anatomy — Labeled

Velocity
  ↑
  |    /\
  |   /  \
  |  /    \___↓(NOTCH)___/‾‾‾‾\_____
  | /                              diastole
  |/__________________________ time →
       ↑         ↑
     Systolic   Notch = early diastolic dip
      peak      (high resistance marker)
Part of WaveformWhat It Represents
Rapid upstrokeSystolic ejection — cardiac contraction
Peak (PSV)Peak systolic velocity
Sharp downtrokeDeceleration after systole
Notch/dipTransient flow reversal = high resistance
Post-notch riseDiastolic flow — reflects downstream compliance
EDV (trough)End-diastolic velocity — reflects placental resistance

Clinical Significance

FindingInterpretation
Notch disappears by 20–22 wksNormal trophoblast invasion — good
Unilateral notch at 22–24 wksBorderline — repeat in 4 weeks
Bilateral notch persisting >24 wksAbnormal — failed spiral artery remodeling
Notch + PI >95th percentileHigh risk for preeclampsia + IUGR
Notch + elevated AFP/low PAPP-ARisk also for placental abruption

Associated Conditions (Persistent Notch)

  1. Preeclampsia — most strongly associated
  2. Intrauterine Growth Restriction (IUGR/FGR)
  3. Placental abruption
  4. Stillbirth / perinatal death
"Persistent notching of the waveform after 24 weeks was associated with increased risk for abruption as well as IUGR and preeclampsia." — Creasy & Resnik's Maternal-Fetal Medicine

Screening Use (First Trimester)

At 11–13+6 weeks, uterine artery PI >95th percentile (>~2.35) combined with PAPP-A <10th percentile and maternal risk factors forms the FMF combined screening algorithm for early-onset preeclampsia, with sensitivity ~75–90% for early preeclampsia at 10% FPR.
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