What is the role of Doppler ultrasound in diagnosing and managing deep vein thrombosis (DVT) or peripheral artery disease (PAD) in a pregnant patient with a history of DVT or PAD?

Doppler Ultrasound in Pregnancy for DVT Diagnosis

In pregnant patients with suspected DVT, compression ultrasound with Doppler imaging of the iliac veins should be the first-line diagnostic test, followed by serial ultrasound on days 3 and 7 if the initial study is negative. 1, 2

Initial Diagnostic Approach

Start immediately with proximal compression ultrasound (CUS) examining the common femoral and popliteal veins plus Doppler assessment of the iliac veins as a single examination. 1, 2 This approach is preferred over:

• D-dimer testing (physiologically elevated throughout pregnancy) 1
• Whole-leg ultrasound (increases false-positives from calf vein findings) 1, 2
• Venography (unnecessary radiation exposure) 1

The American Society of Hematology 2018 guidelines emphasize that proximal ultrasonography with iliac vein imaging is adequate in most pregnant women with suspected DVT. 1

If Initial Ultrasound is Positive

Treat immediately with therapeutic anticoagulation and perform no further testing. 2, 3 A positive proximal CUS is diagnostic and requires no confirmatory venography. 1, 2

If Initial Ultrasound is Negative

The American College of Chest Physicians recommends two options 1:

• Serial proximal CUS on days 3 and 7 (Grade 1B recommendation) 1
• Sensitive D-dimer at presentation (Grade 2B recommendation), with additional follow-up proximal CUS (days 3 and 7) if D-dimer is positive 1

Serial testing is safe and effective: In the largest prospective cohort study, serial proximal ultrasonography with iliac vein imaging over 7 days was associated with only 0.5% false-negative results (1 of 205 patients). 1 A 2013 Canadian study confirmed this safety profile, with a negative predictive value of 99.5% and only 0.49% incidence of VTE during follow-up. 4

A 2020 meta-analysis found that a single negative ultrasound had a pooled false-negative rate of only 1.27%, suggesting that serial testing may be unnecessary in some cases. 5 However, current guidelines still recommend serial testing given the catastrophic consequences of missed DVT in pregnancy. 1

Special Situation: Suspected Isolated Iliac Vein Thrombosis

Suspect isolated iliac DVT when the patient presents with swelling of the entire leg, with or without flank, buttock, or back pain. 1, 3

Standard proximal CUS cannot adequately visualize the iliac veins because the midportion runs beneath the clavicle and compression is impossible in this location. 1 In these cases, the American College of Chest Physicians suggests further testing with: 1

• Doppler ultrasound of the iliac vein (Grade 2C)
• MR venography (Grade 2C)
• Venography (Grade 2C)

Rather than standard serial CUS of the proximal deep veins. 1

The anatomical distribution of DVT in pregnancy differs significantly from non-pregnant patients, with 65% of cases isolated to the iliofemoral veins and 85% occurring on the left side due to compression of the left iliac vein by the right iliac artery and gravid uterus. 3, 4

Why Doppler is Essential

Doppler assessment of the iliac veins is critical because compression maneuvers are impossible in this anatomical location. 1 The absence of a color or Doppler signal within the lumen of the vein indicates thrombosis when compression cannot be performed. 1

Critical Pitfalls to Avoid

• Never rely on D-dimer alone - levels physiologically increase throughout pregnancy and peak at delivery, making negative results unlikely in the second and third trimesters. 1, 6
• Never skip serial testing after negative initial ultrasound - up to 24% of DVTs are detected during serial examinations rather than at presentation. 1
• Never dismiss unilateral leg swelling as "normal pregnancy edema" without objective imaging - pulmonary embolism can be fatal. 3, 7
• Never order whole-leg ultrasound routinely - it is not superior to proximal CUS and increases false-positives. 1, 2

Role in Peripheral Artery Disease

For suspected peripheral artery disease (PAD) in pregnancy, Doppler ultrasound can assess arterial flow and ankle-brachial indices without radiation exposure. However, the provided guidelines focus primarily on venous thromboembolism rather than PAD, as DVT represents the more common and immediately life-threatening vascular complication in pregnancy. 1, 8