Pulmonary embolism (PE) may not be the first thought for clinicians presented with a pregnant woman with leg swelling or sudden shortness of breath, but prompt evaluation for thromboembolism could be lifesaving. And D-dimer testing alone may not reveal the full spectrum of risk.

Pregnant women and women in the postpartum period carry a four- to fivefold higher risk for thromboembolism than nonpregnant women, and about 80% of these events are venous, reported the American College of Obstetricians and Gynecologists (ACOG).

Venous thromboembolism occurs in roughly 0.5-2 per 1000 pregnancies and remains a leading cause of maternal mortality in the US, contributing to more than 9% of pregnancy-related deaths. Given its prevalence and severity, careful attention to risk assessment, prompt diagnosis, and appropriate treatment or prophylaxis is essential, the ACOG reported.

But diagnosing thromboembolism, including PE, is challenging in this patient population because symptoms often mirror normal physiologic changes of pregnancy, making timely testing essential.

Potential Benefit of Clinical Prediction Tools

A recent review in CHEST highlights emerging evidence that clinical prediction tools that include D-dimer testing have potential to safely rule out suspected PE among pregnant women. Two prospective studies published in 2018 and 2019 evaluated the use of D-dimer testing within pregnancy-specific risk-assessment algorithms to rule out PE and reduce the need for chest imaging. Neither study was randomized.

In the first study, Diagnosis of Pulmonary Embolism During Pregnancy, researchers concluded that adiagnostic strategy based on clinical probability, D-dimer, compression ultrasonography, and CT pulmonary angiography (CTPA) can safely rule out PE in pregnant women. In the second, Pregnancy-Adapted YEARS (ARTEMIS), researchers found that pregnancy-adapted YEARS algorithm can safely rule out PE and reduce the need for CTPA in pregnant women.

Additional research is needed to better understand the feasibility of implementing PE risk-assessment tools in pregnancy. And more real-world evidence is needed to confirm the safety and effectiveness of clinical decision rules once they are incorporated into routine practice.

‘A False Sense of Reassurance’

Today, major professional organizations, including the ACOG, continue to advise against relying solely on D-dimer testing because of its limited reliability during pregnancy. In its “Thromboembolism in Pregnancy” Practice Bulletin, ACOG recommends proceeding directly to imaging with ventilation-perfusion (V/Q) scanning or CTPA.

On the surface, using D-dimer testing to rule out PE during pregnancy may seem helpful, but it can offer a false sense of reassurance, said Edward Springel, MD, associate professor of ob/gyn (maternal fetal medicine) at the Virginia Commonwealth University School of Medicine in Richmond, Virginia.

Springel, who co-authored the Thromboembolism in Pregnancy reference guide for Medscape, expounded on the testing limitations as it stands today.

“ACOG’s practice bulletin still discourages use of D-dimer in pregnancy, although the review suggests that D-dimer may be useful in some situations when the doctor thinks that the risk of thromboembolism is low to help reduce the number of unnecessary CT scans,” he told Medscape Medical News.

The two studies in the CHEST review, he said, sought to look at reducing CT scans, but the primary goal should be to not miss a life-threatening thromboembolism.

“CT scans expose the patient to a low amount of radiation — well below the level found to have an impact on a pregnancy,” Springel explained. “In cases of high suspicion for thromboembolism, it is important not to delay the CT scan due to pregnancy. I let the patients know that the risk of the CT scan is small, but missing a blood clot in the lungs can be lethal. The CT is often the right thing for the mother and the baby.”

Given common concerns about fetal risk during imaging, the review article in CHEST emphasizes the importance of clear, evidence-based counseling to support informed decision-making and avoid delays in urgent testing.

Detecting Potentially Life-Threatening PE

For Shameek Gayen, MD, acknowledging the patient’s anxiety over imaging is as important as emphasizing “that modern imaging carries very low fetal radiation exposure and that the greater risk lies in missing a potentially life-threatening PE. I also explain that our diagnostic algorithms are specifically designed to avoid unnecessary exposure whenever safely possible.”

Gayen, assistant professor of clinical thoracic medicine and surgery at the Lewis Katz School of Medicine at Temple University in Philadelphia, shared his common approach in suspect cases.

“I start by reviewing symptoms, vital signs, and risk factors such as immobility, thrombophilia, or prior venous thromboembolism,” he explained. “I would start with bilateral lower extremity dopplers, particularly if lower extremity symptoms are present, as a positive study confirms DVT [deep vein thrombosis], guiding me toward the need for anticoagulation without the need for chest imaging. If no DVT is found, validated decision scores like the pregnancy-adapted YEARS algorithm in conjunction with a D-dimer are valuable. If the D-dimer exceeds the score’s threshold or the pretest probability remains intermediate to high, I would obtain a CTPA or V/Q scan to assess for PE.”

In general, he says he trusts the pregnancy-adapted YEARS algorithm because evidence shows it can safely reduce unnecessary imaging by up to 40% while maintaining very low rates of missed PE.

“However, certain scenarios will still push me toward imaging,” Gayen said. These scenarios include patients with hemodynamic instability, severe or atypical symptoms, or unexplained hypoxia or when D-dimer interpretation is unclear, “especially in late pregnancy, when physiologic elevations can complicate results.”

Springel and Gayen reported having no relevant financial relationships.