What is the role of Doppler ultrasound in obstetrics, particularly for high-risk pregnancies or those with a history of complications?

Doppler Ultrasound in Obstetrics

Primary Recommendation for High-Risk Pregnancies

Umbilical artery Doppler should be initiated when the fetus is viable and intrauterine growth restriction (IUGR) is suspected in high-risk pregnancies, as this significantly reduces perinatal deaths by 29% (from 1.7% to 1.2%), decreases inductions of labor, and reduces cesarean deliveries. 1, 2

Role and Indications

High-Risk Pregnancies Requiring Doppler Surveillance

Doppler ultrasound is reserved exclusively for high-risk pregnancies, as routine use in low-risk populations provides no benefit and may cause iatrogenic prematurity from false-positive results. 1, 3

Specific indications include: 3

• Suspected IUGR or fetal growth restriction
• Hypertensive disorders and preeclampsia
• Diabetes (gestational or pregestational)
• Advanced maternal age
• History of unexplained stillbirth
• Decreased fetal movement
• Oligohydramnios or polyhydramnios
• Multiple gestations
• Chronic renal disease, thyroid disorders, thrombophilia

Low-Risk Pregnancies: No Role

Routine umbilical artery Doppler screening in low-risk populations has not been shown effective in predicting IUGR and should not be performed. 1 A meta-analysis of 11,375 women found no significant difference in outcomes with systematic Doppler use versus controls in unselected populations. 1

Specific Vessel Assessment

Umbilical Artery Doppler: The Gold Standard

This is the only Doppler assessment with Level I evidence demonstrating improved outcomes in IUGR pregnancies. 1

Key findings and their significance: 1

• Normal flow: Continuous forward flow throughout diastole indicates adequate placental perfusion
• Decreased end-diastolic flow: Suggests increasing placental resistance; warrants increased surveillance
• Absent end-diastolic flow (AEDF): Indicates severe placental compromise; consider delivery at ≥34 weeks after corticosteroids 1
• Reversed end-diastolic flow (REDF): Represents advanced placental failure with 70% obliteration of placental vessels; consider delivery at ≥32 weeks 1

Surveillance protocol when IUGR suspected: 1

• Initiate weekly umbilical artery Doppler when fetus is viable
• If normal: Continue weekly surveillance, consider delivery at 38-39 weeks
• If decreased diastolic flow: Increase testing frequency, consider delivery at >37 weeks
• If AEDF: Test 2-3 times weekly, administer corticosteroids if <34 weeks, deliver at 34 weeks
• If REDF: Test 2-3 times weekly or more, deliver at 32 weeks

Middle Cerebral Artery (MCA) and Ductus Venosus: Research Only

Doppler studies of vessels other than the umbilical artery should be reserved for research protocols, as there is currently a lack of randomized trials showing benefit for routine clinical use. 1 While these vessels have prognostic value and can identify fetuses with acidemia (sensitivity 70-90%), they have not been proven to improve outcomes. 1

Uterine Artery Doppler: Limited Screening Value

First-trimester uterine artery Doppler has poor sensitivity (12%) for predicting IUGR and lacks clinical value. 1 Second-trimester screening shows variable results, with positive likelihood ratios of 3.6-14.6 for IUGR depending on the population, but is not recommended for routine screening. 1, 4

Timing and Frequency

Initiate antepartum surveillance at 32-34 weeks' gestation in high-risk pregnancies, though timing must be adjusted based on specific indication and gestational age. 3

Standard surveillance intervals: 1, 3

• Weekly or twice-weekly testing has become standard practice (though optimal interval lacks rigorous evidence)
• With normal umbilical artery Doppler: Weekly intervals acceptable
• With abnormal arterial Doppler: Weekly surveillance if forward flow persists
• With AEDF or REDF: 2-3 times weekly or more frequently
• With oligohydramnios plus abnormal Doppler: 2-3 times weekly

Integration with Other Fetal Surveillance

Doppler assessment should be combined with other surveillance modalities: 1, 3

• Nonstress testing (NST): Twice weekly when IUGR suspected, or more frequently with abnormal Doppler
• Biophysical profile (BPP): Weekly or as indicated by NST results
• Amniotic fluid assessment: Essential component of modified BPP
• Fetal biometry: Serial growth assessments every 2-4 weeks

Clinical Management Based on Doppler Findings

Corticosteroid Administration

Antenatal corticosteroids should be administered if AEDF or REDF is noted at <34 weeks in pregnancies with suspected IUGR. 1 Close observation for 48-72 hours post-administration is reasonable, as there may be transient return of end-diastolic flow in approximately two-thirds of cases. 1

Delivery Timing Algorithm

Based on umbilical artery Doppler findings: 1

• Normal Doppler: Deliver at 38-39 weeks
• Decreased diastolic flow: Deliver at >37 weeks
• AEDF: Deliver at 34 weeks (after corticosteroids)
• REDF: Deliver at 32 weeks (after corticosteroids)

Hospitalization Considerations

Admission may be offered when fetal testing more than 3 times per week is deemed necessary, particularly with AEDF or REDF. 1

Critical Limitations and Caveats

No antenatal test, including Doppler ultrasound, can predict stillbirth related to acute events such as placental abruption or cord accidents. 3 These acute catastrophic events account for many stillbirths even when recent testing was normal.

Common pitfalls to avoid:

• Do not use Doppler screening in low-risk populations 1
• Do not rely on MCA or ductus venosus Doppler alone for clinical management decisions outside research protocols 1
• Do not delay delivery beyond recommended gestational ages with abnormal Doppler findings 1
• Do not use uterine artery Doppler as a standalone screening test 1

The negative predictive value of normal umbilical artery Doppler is excellent, with false negatives (stillbirth within 1 week of normal test) being uncommon. 3 However, ongoing surveillance remains necessary as fetal status can deteriorate between testing intervals.

Intrapartum Considerations

IUGR fetuses require continuous electronic fetal monitoring during labor due to their impaired placental function, chronic hypoxemia, and limited physiologic reserve to withstand repetitive decreases in uteroplacental blood flow with contractions. 5 The intrapartum monitoring represents continuation of close antenatal surveillance that should have been performed throughout pregnancy. 5