Solo Ultrasound for DVT Enough in Pregnancy

It appears to be safe to use a single complete compression ultrasound scan to rule out deep vein thrombosis (DVT) in pregnant women and those who have recently given birth, researchers found.

Among women with a negative sonographic scan, just 1.1% developed a confirmed DVT through 3 months of follow-up, Gre’goire Le Gal, MD, PhD, of the Centre Hospitalier Universitaire de la Cavale Blanche in Brest, France, and colleagues reported online in BMJ.

That rate was consistent with the rate following a normal phlebography - the reference test - in nonpregnant individuals, they noted.

“These data suggest that a negative single complete compression ultrasonography result may safely exclude the diagnosis of deep vein thrombosis in this setting,” they wrote.

Diagnosing DVT during pregnancy, and the immediate postpartum period, can be challenging because pregnancy is a risk factor for venous thromboembolism. Also, some symptoms, including pain, tenderness, and swelling of the legs, occur in both the settings of pregnancy and DVT.

Phlebography is the reference method for diagnosing DVT, but in recent years, compression ultrasonography has become widely used in clinical practice. The technique has been shown to safely rule out DVT in nonpregnant individuals, although it had not been prospectively evaluated during and shortly after pregnancy.

Arteries have thin muscles within their walls to be able to withstand the pressure of the heart pumping blood to the far reaches of the body. Veins don’t have a significant muscle lining, and there is nothing pumping blood back to the heart except physiology. Blood returns to the heart because the body’s large muscles squeeze the veins as they contract in their normal activity of moving the body. The normal activities of moving the body returns the blood back to the heart.

There are two types of veins in the leg; superficial veins and deep veins. Superficial veins lie just below the skin and are easily seen on the surface. Deep veins, as their name implies, are located deep within the muscles of the leg. Blood flows from the superficial veins into the deep venous system through small perforator veins. Superficial and perforator veins have one-way valves within them that allow blood to flow only in the direction of the heart when the veins are squeezed.

A blood clot (thrombus) in the deep venous system of the leg is not dangerous in itself. The situation becomes life-threatening when a piece of the blood clot breaks off (embolus, pleural=emboli), travels downstream through the heart into the pulmonary circulation system, and becomes lodged in the lung. Diagnosis and treatment of a Deep venous thrombosis (DVT) is meant to prevent Pulmonary embolism.

Clots in the superficial veins do not pose a danger of causing pulmonary emboli because the perforator vein valves act as a sieve to prevent clots from entering the deep venous system. They are usually not at risk of causing Pulmonary embolism.

Le Gal and colleagues conducted a prospective study at two tertiary care centers and 18 private practices specializing in vascular medicine in France and Switzerland. The study included 167 pregnant women and 43 women who had given birth within the prior 3 months.

All had been referred for suspected DVT and underwent a single proximal and distal compression ultrasound scan performed by specialists with at least a decade of experience in vascular ultrasound imaging.

Blood clots most often develop in the calf and thigh veins, and less often in the arm veins or pelvic veins. This topic focuses on blood clots in the deep veins of the legs, but diagnosis and treatment of DVT in other parts of the body are similar.

Each year in the United States, between 350,000 and 600,000 people get a blood clot in the legs or in the lungs.

What causes deep vein clots to form?
Blood clots can form in veins when you are inactive. For example, clots can form if you are paralyzed or bedridden or must sit while on a long flight or car trip. Surgery or an injury can damage your blood vessels and cause a clot to form. Cancer can also cause deep vein thrombosis. Some people have blood that clots too easily, a problem that may run in families.

Overall, 10.5% of the women received a diagnosis of DVT, a rate somewhat lower than the rate seen in other European venous thromboembolic diagnostic studies (Circulation 1981; 64: 622-625, J Thromb Haemost 2007; 5: 55-59), according to the researchers.

“However,” they wrote, “the proportion of confirmed venous thromboembolic disease is usually lower in pregnant women, which has been related to a lower threshold for clinical suspicion.”

The vast majority of the women with a negative scan did not receive anticoagulant therapy during the 3-month follow-up period. Of the 10 who had a negative scan but who received full-dose anticoagulation for at least 6 weeks, it was mostly for a superficial thrombophlebitis.

Only two of the women who had a negative scan, and who did not receive anticoagulation during follow-up, developed an objectively confirmed proximal DVT (1.1%, 95% CI 0.3% to 4%).

The authors acknowledged the wide confidence interval, saying that it could be the result of the relatively small sample size. They called for larger studies to confirm the finding.

They noted some additional limitations of the analysis, including the use of both pregnant women and those in the postpartum period, the lack of confirmation by phlebography, and the fact that the researchers did not use measurements of clinical probability and D-dimer before imaging, as is currently used for diagnosis in nonpregnant individuals.

Those limitations “prevent us from drawing firm conclusions,” Le Gal and colleagues wrote. “Further investigations should aim at confirming these results and evaluating the use of compression ultrasonography in a sequential diagnostic strategy including assessment of clinical probability and D-dimer measurement.”

The study was supported by grants from the Projet Hospitalier de Recherche Clinique in France and from the Swiss National Foundation.

The authors reported that they had no conflicts of interest.

Primary source: BMJ
Source reference: Le Gal G, et al “Diagnostic value of single complete compression ultrasonography in pregnant and postpartum women with suspected deep vein thrombosis: prospective study” BMJ 2012; DOI: 10.1136/bmj.e2635.

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