At what time is it appropriate to perform a Doppler (Doppler Ultrasound) study?

Timing of Doppler Ultrasound in Pregnancy

For high-risk pregnancies with suspected fetal growth restriction (FGR), umbilical artery Doppler should be initiated at 26-28 weeks of gestation and performed every 2 weeks if normal, with increased frequency to weekly or 2-3 times per week when abnormalities are detected. 1, 2

Initial Screening in High-Risk Pregnancies

The optimal screening window for women at high risk of FGR is 19-24 weeks' gestation using maternal uterine artery Doppler, which can identify 90% of FGR cases delivering before 32 weeks. 2

• Umbilical artery Doppler surveillance should begin at 26-28 weeks in high-risk pregnancies once the fetus is considered potentially viable 1, 2
• Earlier assessment before 24 weeks should be avoided unless severe abnormalities are suspected, as accuracy and positive predictive values are unacceptable before this gestational age 2

Surveillance Frequency Based on Findings

Normal Umbilical Artery Doppler

• Perform Doppler studies every 2 weeks when umbilical artery flow remains normal 1
• Some protocols recommend testing at 2-4 week intervals when no abnormalities are detected 1

Abnormal Umbilical Artery Doppler with Forward Flow

• Increase to weekly Doppler assessment when decreased end-diastolic velocity is detected (flow ratios >95th percentile) 1, 2
• Weekly surveillance is also recommended for severe FGR with estimated fetal weight <3rd percentile 2

Absent End-Diastolic Velocity (AEDV)

• Perform Doppler studies 2-3 times per week when AEDV is detected 1, 2
• This finding may warrant hospitalization and consideration of antenatal corticosteroid administration 1

Reversed End-Diastolic Velocity (REDV)

• REDV mandates hospitalization with cardiotocography at least 1-2 times daily and Doppler assessment 3 times weekly 2
• This represents critical fetal compromise requiring intensive surveillance 2

Specific Clinical Scenarios

Monochorionic Twin Pregnancies

• Begin routine umbilical artery and middle cerebral artery (MCA) Doppler surveillance at 16-20 weeks of gestation for twin-twin transfusion syndrome (TTTS) screening 1
• In 84% of stage III or IV TTTS cases, abnormal Doppler findings were identified before TTTS diagnosis when surveillance included every-other-week Doppler evaluations 1
• Once TTTS is diagnosed, umbilical artery and ductus venosus Doppler are necessary for staging and clinical management 1

Preeclampsia

• Perform fetal biometry, amniotic fluid assessment, and Doppler studies immediately at diagnosis of preeclampsia, regardless of gestational age 2
• Continue serial surveillance from 26 weeks' gestation when preeclampsia is confirmed and pregnancy continuation is planned 2

Uterine Artery Abnormalities

• When uterine artery pulsatility index is above the 95th centile at 20 weeks, schedule growth ultrasounds and umbilical artery Doppler every 2 weeks 3
• If FGR develops, increase umbilical artery Doppler frequency to weekly 3

Adjunctive Doppler Studies

Middle Cerebral Artery (MCA) Doppler

• Consider MCA Doppler at 32 weeks or later in pregnancies with FGR 1
• Perform every 2-3 weeks if umbilical artery Doppler is normal 1
• MCA Doppler should not be relied upon for routine management as a primary screening modality; it is an adjunctive tool 2

Ductus Venosus Doppler

• Ductus venosus studies are of unclear value as a component of routine monochorionic twin surveillance 1
• However, ductus venosus Doppler is recommended following identification of atypical findings such as overt TTTS, isolated polyhydramnios, or coexisting FGR 1

Low-Risk Pregnancies

Routine Doppler ultrasound in low-risk or unselected populations is not recommended, as it does not confer benefit on mother or baby and does not result in improved perinatal outcomes. 1, 4

• 83% of international guidelines concur that there is no role for universal Doppler screening in low-risk populations 2
• Routine third-trimester ultrasound at 36 weeks for growth assessment is recommended by some guidelines, but Doppler is not part of routine low-risk surveillance 2

Critical Timing Considerations for Optimal Assessment

• The optimal window for comprehensive assessment is 30-35 weeks if follow-up imaging is needed, as physiologic myometrial thinning after 35 weeks can limit accurate assessment 2
• Avoid delaying Doppler assessment once FGR is suspected, as umbilical artery Doppler reduces perinatal death by 38% in high-risk pregnancies when incorporated into management 2

Common Pitfalls to Avoid

• Do not perform detailed Doppler assessment before 24 weeks unless severe abnormalities are suspected, as accuracy is inadequate 2
• Do not rely on MCA or ductus venosus Doppler as primary screening tools; umbilical artery Doppler is the primary modality 2
• Do not use the same surveillance protocol for all high-risk conditions; tailor frequency based on specific Doppler findings 1, 2
• When oligohydramnios accompanies IUGR with absent or reversed end-diastolic flow, surveillance up to 2-3 times per week is recommended 1