Left-leg DVT more common during pregnancy

The anatomic distribution of deep vein thromboses differed among pregnant and nonpregnant women, findings from a meta-analysis suggested, and pregnant women were more likely to experience left-sided deep vein thrombosis.

Although results of observational studies have suggested this link before, little remains known about the anatomic distribution of DVT in pregnant women because of the risks involved with exposing the fetus to radiation or contrasting agents necessary for noninvasive imaging studies.

Researchers analyzed six studies involving 124 pregnant women and abstracted data concerning the side of the thrombosis; the anatomic distribution of the thrombosis; and the involvement of each venous segment at the time of DVT diagnoses. Eligible studies consisted of case series or observational cohorts that involved three or more participants in which DVT was diagnosed using compression ultrasonography, MRI, CT or venography.

The researchers found that 84 of 96 patients (88%) for which the affected side was known experienced left-leg involvement and that 87 of the 122 thromboses (71%) were restricted to the proximal veins without calf-vein involvement. Furthermore, among cases of proximal thromboses, 56 of 87 cases (64%) occurred in the iliac and/or femoral vein.

“These observations strongly suggest that the anatomic distribution of DVT in pregnant women, and perhaps the pathophysiology of the condition, may indeed differ from that reported in the general population,” the researchers wrote.

Data from previous studies involving nonpregnant patients indicated that proximal thrombosis involving calf veins was common (58% to 87%), whereas isolated proximal vein thrombi were uncommon (0% to 13%).

“We might speculate that among pregnant women, a May-Thurner–like syndrome brought on by compression of the left iliac vein by the gravid uterus … plays a major role in the increased incidence of iliofemoral DVT in late pregnancy,” the researchers wrote, but noted that DVT frequency among pregnant women was equal during all three trimesters. “Until prospective diagnostic studies are available for pregnant patients, it may be prudent to conduct a routine examination of the iliofemoral venous system when a pregnant patient presents with suspected DVT.”

Chan W-S. CMAJ. 2010;doi:10.1503/cmaj.091692.