D-dimer Interpretation in Pregnancy

Physiologic Changes of D-dimer During Pregnancy

D-dimer levels increase progressively throughout normal pregnancy, with values rising by approximately 39% in each trimester compared to the previous one 1
Mean D-dimer concentrations during pregnancy have been reported as:

A retrospective study showed D-dimer had only 73% sensitivity and 15% specificity for pulmonary embolism in pregnancy, with a negative likelihood ratio of 1.8, making it inadequate to rule out pulmonary embolism 2, 3
The American Thoracic Society/Society of Thoracic Radiology guidelines recommend against using D-dimer to exclude pulmonary embolism in pregnancy due to these limitations 2, 4

Despite limitations, a normal D-dimer value still has some exclusion value for pulmonary embolism in pregnant women, particularly in early pregnancy 5, 6
If D-dimer testing is performed and results are normal, it may help avoid unnecessary radiation exposure to the fetus 6, 7
If D-dimer is elevated:

Clinical assessment with high index of suspicion (common symptoms like shortness of breath and rapid heart rate may be normal in pregnancy) 5, 7
Consider D-dimer testing (recognizing limitations):
Bilateral compression ultrasound of lower extremities:
Appropriate imaging based on clinical context and local expertise (perfusion lung scan or CT pulmonary angiography) 5, 7

The American Thoracic Society/Society of Thoracic Radiology explicitly recommends against using D-dimer to exclude pulmonary embolism in pregnancy 8
For pregnant women with suspected DVT, initial evaluation with proximal compression ultrasound (CUS) is recommended over other tests, including D-dimer 9, 10
If initial proximal CUS is negative but clinical suspicion remains high, serial CUS testing is recommended 9
For suspected iliac vein DVT, additional imaging with MRI or venography may be necessary 9

A clinical prediction model for DVT in pregnancy includes three variables: left leg symptoms, calf circumference difference ≥2 cm, and first trimester presentation 9, 10
With none of these criteria, DVT was not diagnosed in studied populations (0%) 10
With one variable, DVT occurred in 16.4% of cases 9
With two or three variables, DVT occurred in 58.3% of cases 9, 10

Avoid unnecessary radiation exposure by using ultrasound as the first-line imaging test when DVT is suspected 9, 8
Do not rely on a negative D-dimer to exclude thromboembolic events in pregnant women 8

D-dimer testing has limited but not negligible utility in the first trimester for excluding venous thromboembolism (VTE), though it should never be used as the sole diagnostic test and proximal compression ultrasonography remains the recommended first-line investigation, as recommended by the American College of Chest Physicians 11

D-dimer levels begin rising early in pregnancy, with mean concentrations increasing from pre-conception levels of 0.43 mg/L to 0.58 mg/L in the first trimester—representing a 39% relative increase 12

For suspected deep vein thrombosis (DVT) in first trimester, begin with proximal compression ultrasonography rather than D-dimer testing, as recommended by the American College of Chest Physicians with a Grade 2C recommendation for proximal CUS versus a moderately sensitive D-dimer 11
The American College of Chest Physicians explicitly recommends proximal CUS over D-dimer, with a Grade 1B recommendation versus highly sensitive D-dimer 11

First trimester presentation is itself a high-risk variable for DVT (adjusted OR 63.4), meaning clinical suspicion should be heightened during this period, as noted by the American College of Chest Physicians 11
When combined with left leg symptoms or calf circumference difference ≥2 cm, the probability of DVT reaches 58.3%, as reported by the American College of Chest Physicians 11