D Dimer during Pregnancy
Pulmonary embolism is the sixth leading cause of maternal mortality in the United States. Diagnosis of pulmonary embolism during pregnancy is particularly challenging because many of the most common signs and symptoms of pulmonary embolism such as dyspnea, tachycardia and tachypnea, occur in normal pregnancy.
The most widely validated pretest probability (PTP) score for pulmonary embolism in the nonpregnant patient is the Wells score. Wells score is calculated using the following criteria:
- Clinical symptoms of deep vein thrombosis (DVT) (3 points)
- Other diagnoses are less likely than PE (3 points)
- Heart rate >100 (1.5 points)
- Immobilization three or more days or surgery in previous four weeks (1.5 points)
- Previous DVT/PE (1.5 points)
- Hemoptysis (1 point)
- Malignancy (1 point)
Unfortunately, the Wells score has limited value in determining the likelihood of pulmonary embolism in the pregnant population because leg edema and tachycardia are common in normal pregnancy and risk factors such as malignancy or recent surgery are uncommon. For these reasons, most obstetrical guidelines suggest against the use of clinical prediction rules to rule out deep vein thrombosis or pulmonary embolism.
D-dimer levels have limited utility for the diagnosis of venous thromboembolism or pulmonary embolism in pregnancy. D-dimer levels increases with gestational age and slowly declines postpartum. Interpretation of D-dimer levels during pregnancy and the puerperium is complicated by a lack of pregnancy specific reference ranges. The sensitivity and specificity of D-Dimer for pulmonary embolism during pregnancy have been estimated to be 73 and 15 percent, respectively. Considering the low sensitivity (high false negative rate) and specificity (high false positive rate) of D-dimer during pregnancy, an elevated D-dimer is not diagnostic of pulmonary embolism and a value <500 ng/mL cannot rule it out.
Neither the Wells score nor D-Dimer can be used during pregnancy to rule out venous thromboembolism or pulmonary embolism. A definitive diagnosis of pulmonary embolism in the pregnant patient is made by the demonstration of a high probability ventilation perfusion (V/Q) scan or visualization of clot by computed tomographic pulmonary angiogram (CTPA), magnetic resonance, or contrast angiography.
References
- McLean K, Cushman M. Venous thromboembolism and stroke in pregnancy. Hematology Am Soc Hematol Educ Program. 2016;2016(1):243-250.
- Wan T et al. Guidance for the diagnosis of pulmonary embolism during pregnancy: Consensus and controversies. Thromb Res. 2017;157:23-28.
- Chan WS, et al. D-dimer testing in pregnant patients: towards determining the next 'level' in the diagnosis of deep vein thrombosis. J Thromb Haemost 2010; 8:1004.
- Damodaram M, et al. D-dimers as a screening test for venous thromboembolism in pregnancy: is it of any use? J Obstet Gynaecol 2009; 29:101.
