Single complete compression ultrasonography could be used to rule out suspected deep vein thrombosis (DVT) during pregnancy or the postpartum period, the findings of a study in the BMJ suggest.

A total of 210 women with suspected DVT were referred for vascular ultrasound examination of the venous system of both legs. A hundred and sixty seven were pregnant, the remaining 43 women presented during the postnatal period. All patients were scanned by highly experienced operators.

The clinical suspicion of DVT was confirmed most commonly in the first trimester and least in the second trimester. The vast majority of confirmed DVTs occurred in the third trimester and puerperium, see table 1.

DVT was diagnosed in 22 cases (10.5%). As is often the case, DVTs were more common in the left leg, 18 out of 112 suspected cases (16.1%) vs 4 out of 88 (4.5%) on the right, p = 0.02. It is thought that compression of the left common iliac artery by the right common iliac artery may be a factor.

The convention adopted to define a false-negative scan result was a thromboembolic event within three months of an initially negative scan. Of the 188 women with a negative scan, ten had anticoagulant therapy (mainly for superficial thrombophlebitis) and one was lost to follow up.

Two of the remaining 177 women developed a thromboembolic event. Both were in their twenties and in the third trimester. Neither had risk factors in their history though clinically both were classified as ‘intermediate risk’.

One returned the day after her initial test because of increasing symptoms and on re-scanning clearly had a DVT. The second case followed bed rest for preterm labour and emergency caesarean section. Her DVT was identified five days after operation. The former case constituted a genuine false-negative result. In the latter case the events after her initial scan appear to be more relevant.

The three-month thromboembolic rate was 2/177, 1.1% (95% CI: 0.3-4.0%). No false-negative results were identified among women initially scanned in the puerperium.

Leg pain and swelling is a common complaint during pregnancy and can signify a DVT. Untreated DVTs can cause life-threatening embolic events but false-positive diagnoses expose women to unnecessary anticoagulation, a treatment not without risk. So having a reliable test is important.

X-ray venography is considered the gold standard test for DVT but unlike ultrasonography it is invasive and may expose the fetus to ionising radiation. Previous studies have shown that thromboembolic events within three months of a negative venogram or compression ultrasonography occur in around 1.3 and 1.0% of cases respectively. Although the findings of this observational ‘management outcome study’ are in line with this, a direct comparison with venography would be useful.

Dr Chris Barclay

• Le Gal G, Kercret G, Ben Yahmed K et al on behalf of the EDVIGE study group. Diagnostic value of single complete compression ultrasonography in pregnant and postpartum women with suspected deep vein thrombosis: prospective study. BMJ 2012;344:e2635