Uterine Artery doppler during NT screening

Role of Uterine Artery doppler

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Uterine artery Doppler assesses blood flow resistance in the uterine arteries, which supply the placenta. Abnormal flow patterns in the first trimester (11–14 weeks) can indicate impaired placentation, which may lead to complications like.

• Preeclampsia
• Fetal Growth Restriction (FGR)
• Placental insufficiency

Patient Preparation

No special preparation is needed for first-trimester Umbilical Artery Doppler assessment. A moderately full bladder may aid in optimal imaging of the fetal anatomy during NT screening.

Technique

Using a transabdominal probe (3.5–5 MHz), the umbilical cord is visualized near the fetal insertion site. Color Doppler is applied to locate the umbilical artery. Pulsed-wave Doppler is then used to record waveforms, ensuring the angle of insonation is <30°. Record at least 3 uniform waveforms in the absence of fetal movement.

Interpretation

While not standard in NT screening, the presence of high resistance or absent/reversed end-diastolic flow (if observed) may indicate early signs of placental insufficiency. However, definitive interpretation should be deferred to second trimester when vascular beds are more developed.

Clinical Use

Umbilical artery Doppler during NT screening is generally reserved for research or select high-risk pregnancies. Its use is more clinically valuable from 20 weeks onward for evaluating fetal well-being and guiding FGR management.

Normal Ranges During NT Screening (11–13+6 weeks)

Parameter	Normal Range	Clinical Interpretation
Pulsatility Index (PI)	< 2.5 (mean ~1.5–2.3)	Elevated PI (>95th percentile) may suggest impaired placental perfusion
Resistance Index (RI)	0.45–0.80	RI > 0.80 may indicate increased resistance in uterine arteries
Peak Systolic Velocity (PSV)	50–70 cm/s	Normal range; may vary depending on gestational age and equipment sensitivity
A-wave (in uterine artery waveform)	Forward flow (positive A-wave)	Absent or reversed A-wave suggests increased downstream resistance or abnormal placental implantation

Note: Bilateral uterine artery notching and elevated PI (>95th percentile) are associated with increased risk of early-onset preeclampsia, placental insufficiency, and fetal growth restriction (FGR).

These indices are often plotted against gestational age-based reference charts or MoMs (Multiples of Median) for interpretation.

Clinical Implications of High Uterine Artery PI

Condition	Explanation
Early-onset Preeclampsia (PE)	High PI (>95th percentile) reflects increased resistance in uterine arteries, which is a key marker for predicting early PE.
Fetal Growth Restriction (FGR / IUGR)	Poor placental blood flow leads to inadequate fetal nutrition and oxygenation, resulting in restricted growth.
Placental Insufficiency	Impaired remodeling of spiral arteries causes high-resistance flow, leading to a dysfunctional placenta.
Increased Risk of IUFD (Intrauterine Fetal Demise)	In severe cases, poor placental perfusion may result in fetal demise.

What to Do if High PI is Detected

Action	Details
Follow-up Anomaly Scan	Schedule a detailed fetal anomaly scan at 18–22 weeks to assess structural development.
Serial Growth Monitoring	Conduct regular fetal biometry scans during 2nd and 3rd trimesters to monitor growth trends.
Aspirin Prophylaxis	Start low-dose aspirin (75–150 mg daily) before 16 weeks to reduce the risk of preeclampsia.
Monitor Preeclampsia Signs	Track maternal blood pressure, check for proteinuria, and observe for clinical symptoms.
Specialist Referral	Refer to a maternal-fetal medicine (MFM) specialist if high-risk or severe findings are present.

Clinical Interpretation of Low Uterine Artery PI (< 5th percentile) during NT Screening (11–13+6 weeks)

Aspect	Explanation
Normal Trophoblastic Invasion	Suggests good placental development due to adequate remodeling of spiral arteries and reduced vascular resistance.
Low Risk of Preeclampsia or FGR	Associated with a lower likelihood of early-onset preeclampsia, fetal growth restriction (FGR), or placental insufficiency.
Good Uteroplacental Perfusion	Indicates efficient blood flow from mother to placenta, supporting optimal fetal development.
No Immediate Concern	Typically requires no intervention if other screening parameters (NT, DV flow, PAPP-A, etc.) are normal.

Note: Interpretation should always be in context—combine with NT thickness, serum markers (PAPP-A, free β-hCG), ductus venosus flow, and clinical risk factors.

Clinical Interpretation of High Uterine Artery RI (> 0.80)

Condition	Explanation
Increased Uterine Vascular Resistance	High RI reflects restricted blood flow in uterine arteries, typically due to inadequate trophoblastic invasion and spiral artery remodeling.
Risk of Early-Onset Preeclampsia	Elevated RI is a predictor of impaired placental perfusion and increased risk for preeclampsia, especially when combined with other markers.
Fetal Growth Restriction (FGR / IUGR)	Inadequate maternal blood supply to the placenta may result in poor fetal growth.
Placental Insufficiency	Persistent high resistance indicates poor uteroplacental circulation and inefficient nutrient/oxygen exchange.
Increased Likelihood of Abnormal Doppler Findings Later	May correlate with uterine artery notching and abnormal PI or A-wave later in pregnancy.

Note:
High RI alone should not be used in isolation—always interpret alongside:

• Uterine artery PI and A-wave
• NT thickness
• Biochemical markers (PAPP-A, free β-hCG)
• Maternal clinical risk factors

Clinical Interpretation of Low Uterine Artery RI (< 0.40–0.45)

Aspect	Explanation
Good Spiral Artery Remodeling	Low RI indicates reduced resistance in uterine arteries, reflecting normal trophoblastic invasion and placental development.
Low Risk of Preeclampsia or FGR	Associated with decreased likelihood of uteroplacental insufficiency, preeclampsia, and fetal growth restriction.
Optimal Uteroplacental Perfusion	Suggests healthy maternal blood flow to the placenta, supporting normal fetal growth and development.
No Immediate Concern	Low RI alone is not considered pathological; typically no intervention needed if other parameters (PI, NT, PAPP-A) are normal.

Note:
Interpretation should always be done in context—combine RI findings with:

• Uterine artery PI and presence of early diastolic notch
• NT measurement
• Serum markers (PAPP-A, free β-hCG)
• Ductus venosus Doppler
• Maternal clinical history and risk factors

Clinical Interpretation of Absent or Reversed A-Wave in Uterine Artery Doppler (11–13+6 Weeks)

Condition	Explanation
Impaired Spiral Artery Remodeling	Absent or reversed A-wave reflects high resistance and poor transformation of spiral arteries by invading trophoblasts.
Early Marker of Placental Insufficiency	This waveform abnormality is associated with compromised placental perfusion and may precede other signs of dysfunction.
High Risk of Early-Onset Preeclampsia (PE)	Strongly linked to increased risk of early-onset PE, particularly when combined with high PI/RI and low PAPP-A.
Fetal Growth Restriction (FGR/IUGR)	May indicate insufficient maternal blood flow to the placenta, increasing the risk of restricted fetal growth and hypoxia.
Possible Indication for Prophylaxis	Low-dose aspirin initiated before 16 weeks may help reduce risk of PE and improve outcomes in high-risk cases.

Clinical Note:
Absent or reversed A-wave should always be interpreted in combination with:

• Uterine artery PI and RI
• NT measurement
• Serum markers (PAPP-A, free β-hCG)
• Ductus venosus flow
• Maternal risk factors (e.g., history of PE, chronic hypertension, autoimmune conditions)