Introduction: The accuracy of ultrasound (US) for diagnosing lower extremity deep vein thrombosis (DVT) in non-pregnant patients has been well validated. However, in pregnant women with suspected DVT and an initial negative US (with imaging of the iliac veins), serial US is recommended. We aimed to determine the ability of single negative US to exclude DVT in symptomatic pregnant women. Methods: Two authors independently reviewed the following databases: MEDLINE, PubMed and EMBase from inception until May 2017. Three authors reviewed all full text papers and data were extracted from included studies by four authors. An overlap among study populations was identified in 4 of the manuscripts, all from one multicentre Canadian study. Two authors performed data re-extraction from the hard copy research charts from this study. We assessed the risk of bias using the CLARITY group tool for prognostic studies. Results: Of 109 potentially relevant articles, 8 studies (7 prospective studies and 1 retrospective) were included. Risk of bias was low for the included populations, and low or moderate for method of measurement and for completeness of follow up. A total of 635 pregnant patients with symptoms of DVT had an initial negative US examination. Of those, 6 had positive DVT during serial US (0.94%) and 3 developed DVT during 3-month follow-up after serial ultrasound (0.47%). Using random-effects model, the pooled false negative rate of a single ultrasound was 1.27% (95% confidence interval, 0.42 to 2.56), I2= 27%. Conclusion: The false negative rate of a single ultrasound with iliac vein imaging for DVT in pregnancy is low. Our results will help inform shared decision making around planning repeat ultrasound scans in these patients.
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