Abstract: Thirteen studies (1053 women) reported the accuracy of 3D SIS for focal uterine abnormalities; 11 of these (846 women) were suitable for meta-analysis, and eight reported accuracy according to the type of focal abnormality. The design of the included studies seems applicable. The main problem involving the quality of included studies is insufficient reporting of study methods, resulting in unclear risk of bias for several of the quality domains assessed. Therefore, we considered the overall quality of the evidence as low. The summary estimate (11 studies reporting absence or presence of abnormality at 3D SIS) for sensitivity was 94.5% (95% confidence interval (CI) 90.6% to 96.9%) and for specificity 99.4% (95% CI 96.2% to 99.9%). Meta-analysis of the eight studies (N = 716) directly comparing 2D SIS versus 3D SIS showed summary sensitivity of 96.9% (95% CI 91.9% to 98.8%) and summary specificity of 99.5% (95% CI 96.1% to 100%) for 3D SIS. For 2D SIS, summary sensitivity was 90.9% (95% CI 81.2% to 95.8%) and summary specificity was 96.3% (95% CI 86.1% to 99.1%). The difference in accuracy between 2D SIS and 3D SIS was non-significant (P values of 0.07 for sensitivity and 0.10 for specificity). Low-quality evidence suggests that 3D SIS may be very accurate in detecting intracavitary abnormalities. Meta-analysis revealed no statistically significant differences between 2D SIS and 3D SIS. Summary sensitivity and summary specificity are higher for 3D SIS, but margins of improvement are limited because 2D SIS is already very accurate. When the technology and appropriate expertise are available, 3D SIS offers an alternative to 2D SIS. Both 2D SIS and 3D SIS should be considered alternatives to diagnostic hysteroscopy when intracavitary pathology is suspected in subfertile women and in those with abnormal uterine bleeding.

Plain-language summary: Review authors searched for studies published from inception until March 2016 and found 13 studies (in total 1053 women), eight of which directly compared 3D SIS versus 2D SIS. Data included all women reporting abnormal menstrual bleeding or difficulty getting pregnant. The number of patients in these studies varied from 23 to 180 women. In all studies, researchers checked the results of 2D SIS and 3D SIS against results obtained when a camera was used to look inside the womb (hysteroscopy); this is expected to give the true picture but is also more painful for the patient. All studies were performed in the usual way. Some studies did not report several items that might have influenced the results. For example, not all studies made it clear that the person evaluating the ultrasound pictures was unaware of the hysteroscopy results, and vice versa. The main problem involving the quality of included studies is insufficient reporting of study methods, resulting in unclear risk of bias for several of the quality domains assessed. Therefore, review authors considered the overall quality of the evidence as low. Low-quality evidence suggests that 3D SIS may be very accurate in detecting polyps and fibroids. Our analysis revealed no clear differences between 2D SIS and 3D SIS. Summary results are higher for 3D SIS but margins of improvement are limited because 2D SIS is already very accurate. Results show that 2D SIS missed a fibroid or polyp in 9 of 100 women and 3D SIS missed a polyp or fibroid in 3 of 100 women who had them. In 4 of 100 women, 2D SIS indicated the presence of polyps or fibroids when there were none, and in less than 1 in 100 women, 3D SIS was wrong. In theory, if both tests were used in a group of 1000 women with abnormal menstrual bleeding, 300 with fibroids or polyps, 27 of the 300 women with polyps/fibroids will be missed by 2D SIS, and 9 of 300 will be missed by 3D SIS. 3D SIS is an alternative to 2D SIS for which the technology and appropriate expertise are available. Both 2D SIS and 3D SIS should be considered alternatives to diagnostic hysteroscopy when intracavitary pathology is suspected in subfertile women and in those with abnormal uterine bleeding.