DVT Is More Likely to Occur on the Left Side in Pregnant Women

Laurie Barclay, MD

March 30, 2010

March 30, 2010 — Deep vein thrombosis (DVT) is more likely to occur on the left side, particularly the left leg, in pregnant women, according to the results of a review reported online March 29 in the Canadian Medical Association Journal.

"Prospective studies of nonpregnant patients have demonstrated that most ...DVTs of the lower extremity originate in the calf veins and progress proximally, but the anatomic distribution of thromboses in pregnant patients is unclear," write Wee-Shian Chan, MD, MSc, from the University of Toronto in Ontario, Canada, and colleagues. "An understanding of the anatomic distribution of ...DVT in pregnancy has important implications for optimizing diagnostic imaging protocols. We undertook this study to determine the anatomic distribution of ...DVT of the lower extremity in symptomatic pregnant patients."

Using prespecified criteria, the reviewers systematically searched MEDLINE (1966 to January 2009), Embase (1980 to January 2009), and the Cochrane Library for articles including objective diagnostic and anatomic data for unselected or consecutive symptomatic pregnant patients with DVT.

From an initial list of 1098 titles, 6 studies enrolling a total of 124 pregnant women with DVT met the selection criteria. Among 96 patients for which the side affected was reported, 84 (88%) had involvement of the left leg, and 87 (71%) of 122 thromboses occurred in the proximal veins without involvement of the calf veins. Among these proximal DVTs, 56 (64%) were limited to the iliac and/or femoral vein.

"Despite a paucity of studies in this area, the results of our review suggest that the anatomic distribution of ...DVT in pregnant women differs from that for nonpregnant patients," the study authors write. "In addition to what was previously known — that left-sided ...DVT is more common in pregnancy — we also found that proximal ...DVT, restricted to the femoral or iliac veins, is also more common (> 60% of cases). If confirmed by larger studies, these findings could affect our understanding of the pathophysiology and derivation of diagnostic algorithms for examination of pregnant women with suspected ...DVT."

Study Limitations

Limitations of this study include pooling of small observational studies, exclusion of articles in languages other than English, possible reporting bias and selection bias, and possible underestimation of the prevalence of isolated calf vein or iliac vein thrombosis.

Commentary: Site of Thrombosis May Vary

In a related commentary, Risto Kaaja, MD, PhD, from Turku University and Satakunta Central Hospital in Pori, Finland, notes that the site of the thrombosis and propagation in pregnant women can vary depending on thrombophilic status, possible immobilization, and varying degrees of the effect of a growing uterus on venous stasis in the lower limbs.

"The results of Chan and colleagues' study suggest that the distribution of ...DVT in pregnant women may differ from that in nonpregnant women," Dr. Kaaja writes. "The increased prevalence of isolated proximal ...DVT is clinically important because of the high risk of pulmonary embolism (40%–50%). These findings should be confirmed by larger prospective studies."

This study received no external funding. Coauthor Frederick A. Spencer, MD, is the recipient of a Career Investigator Award from the Heart and Stroke Foundation of Ontario. Coauthor Jeffrey S. Ginsberg, MD, is the recipient of a Career Investigator Award from the Heart and Stroke Foundation of Ontario and the David Braley and Nandy Gordon Chair in Thromboembolic Disease. Dr. Kaaja has disclosed no relevant financial relationships.

CMAJ. Published online March 29, 2010.

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