Optimal Timing for Fetal Doppler Ultrasound
For high-risk pregnancies with suspected or confirmed fetal growth restriction, umbilical artery Doppler should be initiated once FGR is diagnosed and performed weekly, with increased frequency (2-3 times per week) if absent end-diastolic velocity is detected. 1
Clinical Context Determines Timing
The appropriate timing for fetal Doppler ultrasound depends entirely on the clinical indication and risk profile:
Low-Risk Pregnancies
- Routine Doppler screening is not recommended in uncomplicated, low-risk pregnancies 2
- Standard anatomic ultrasound at 18-22 weeks does not routinely include Doppler assessment in this population
- If growth concerns arise later (fundal height >3 cm less than gestational age), Doppler can be added at that time 2
High-Risk Pregnancies: Screening Window
For women at high risk of fetal growth restriction, the optimal screening window is 19-24 weeks' gestation 1
- Maternal uterine artery Doppler at 19-24 weeks can identify 90% of FGR cases delivering before 32 weeks with a 10% false-positive rate 1
- 20 weeks is the single most appropriate gestation in the second trimester for uterine artery Doppler studies if enhanced screening is desired 3
- Umbilical artery Doppler at 19-22 weeks shows significant association with small-for-gestational-age infants, particularly those below the 5th centile 4
Preeclampsia: Immediate Assessment
When preeclampsia is diagnosed at any gestational age, fetal Doppler should be performed immediately 1
- Umbilical artery and uterine artery Doppler studies should be obtained at the time of preeclampsia diagnosis 1
- Serial surveillance from 26 weeks onward is then recommended if pregnancy continuation is planned 1, 2
Surveillance Protocol Once FGR is Diagnosed
The frequency of Doppler assessment escalates based on severity:
Weekly Doppler Assessment
- Indicated when FGR is diagnosed with decreased end-diastolic velocity (flow ratios >95th percentile) 1
- Also recommended for severe FGR with estimated fetal weight <3rd percentile 1
2-3 Times Per Week
- Required when absent end-diastolic velocity (AEDV) is detected in the umbilical artery 1
- This frequency reflects the potential for rapid deterioration 5
Daily to Multiple Times Daily
- Reversed end-diastolic velocity (REDV) mandates hospitalization with cardiotocography at least 1-2 times daily 1
- Doppler assessment should occur 3 times weekly in this critical scenario 1
Specific High-Risk Conditions
Placenta Accreta Spectrum Disorder
- Duplex Doppler should be performed whenever possible when evaluating for placental invasion 1
- Follow-up imaging at 28-32 weeks for women with placenta previa overlying a uterine scar 1
Twin Pregnancies
- Monochorionic twins require Doppler surveillance for twin-twin transfusion syndrome, selective intrauterine growth restriction, and other complications 1
- Dichorionic twins need Doppler only when growth discrepancy is identified 1
Critical Timing Considerations
Avoid MRI and detailed Doppler assessment before 24 weeks unless severe abnormalities are suspected, as accuracy, sensitivity, and positive predictive values are unacceptable before this gestational age 1
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 1
Common Pitfalls to Avoid
- Do not perform routine Doppler in low-risk pregnancies - this increases interventions without improving outcomes 2
- Do not delay Doppler assessment once FGR is suspected - umbilical artery Doppler reduces perinatal death by 38% in high-risk pregnancies when incorporated into management 1
- Do not rely on middle cerebral artery or ductus venosus Doppler for routine management - these are adjunctive tools, not primary screening modalities 1
- Do not perform growth scans more frequently than every 2 weeks - inherent biometric error makes shorter intervals unreliable 5
Most Predictive Parameters
The cerebroplacental ratio and umbilical artery pulsatility index have the highest diagnostic accuracy (81.11%) for predicting adverse fetal outcomes 6
These parameters outperform other Doppler indices and should be prioritized when assessing fetal well-being in high-risk pregnancies 6