Abstract: We included 11 studies (four CTPA, five lung scintigraphy, two both) with a total of 695 CTPA and 665 lung scintigraphy results. Lung scintigraphy was applied by different techniques. No MRA studies matched our inclusion criteria. Overall, risk of bias and concerns regarding applicability were high in all studies as judged in light of the review research question, as was heterogeneity in study methods. We did not undertake meta-analysis. All studies used clinical follow-up as a reference standard, none in a manner that enabled reliable identification of false positives. Sensitivity and negative predictive value were therefore the only valid test accuracy measures. The median negative predictive value for CTPA was 100% (range 96% to 100%). Median sensitivity was 83% (range 0% to 100%). The median negative predictive value for lung scintigraphy was 100% (range 99% to 100%). Median sensitivity was 100% (range 0% to 100%). The median frequency of inconclusive results was 5.9% (range 0.9% to 36%) for CTPA and 4.0% (range 0% to 23%) for lung scintigraphy. The overall median prevalence of pulmonary embolism was 3.3% (range 0.0% to 8.7%). Both CTPA and lung scintigraphy seem appropriate for exclusion of pulmonary embolism during pregnancy. However, the quality of the evidence mandates cautious adoption of this conclusion. Important limitations included poor reference standards, necessary assumptions in the analysis regarding inconclusive test results and the inherent inability of included studies to identify false positives. It is unclear which test has the highest accuracy. There is a need for direct comparisons between diagnostic methods, including MR, in prospective randomized diagnostic studies.

Plain-language summary: We found 11 studies (current until July 2015) that described 695 computed tomography pulmonary angiography results, 665 lung scintigraphy results and no magnetic resonance angiography results. Studies on lung scintigraphy used varying techniques. Overall, these studies were of poor quality; therefore, we could not analyse results together to obtain a single estimate of their accuracy. The identified studies followed-up patients clinically to confirm the absence of pulmonary embolism as revealed on the initial scan, so information could be used to draw conclusions only on the ability of these imaging tests to exclude pulmonary embolism, not on their ability to establish the diagnosis. Both computed tomography pulmonary angiography and lung scintigraphy appear appropriate for excluding pulmonary embolism in pregnancy. Almost no cases were missed, especially when the imaging test indicated the absence of disease without a doubt. However, this result should be interpreted with care because of the low quality of and variation between identified studies. Around 5% of the scans were unclear, but this percentage was as high as 36% in one study. About 3% of all women included in the studies had pulmonary embolism. We do not know which of the tests is better because tests were not directly compared in the same patients, and because aspects besides test accuracy need to be taken into account. Major limitations of this review include the use of clinical follow-up within studies to confirm the absence of disease, unclear test results and the inability of studies to provide information on the accuracy of these tests in establishing rather than rejecting the diagnosis. High-quality research is needed to investigate the use of computed tomography pulmonary angiography, lung scintigraphy and magnetic pulmonary angiography in the same patient groups.