Accuracy of first trimester ultrasound in the diagnosis of an intrauterine pregnancy prior to the development of the yolk sac: a systematic review and meta-analysis

OBJECTIVES: To evaluate the diagnostic accuracy of ultrasound in confirming intrauterine pregnancy location prior to development of the yolk sac.

METHODS: The systematic review was conducted in accordance with PRISMA and registered with PROSPERO. We searched MEDLINE, Embase and the Cochrane Library for citations. Studies were selected in a two-stage process and their data extracted by two reviewers. Accuracy measures were calculated for each test i.e. gestation sac, double decidual sac sign, intradecidual sign, chorionic rim sign and yolk sac. Individual study estimates were plotted in summary ROC and forest plots for examination of heterogeneity. The quality of studies was assessed using the QUADAS-2 checklist.

RESULTS: Seventeen studies including 2564 women were selected from 19959 potential papers. Following meta-analysis, a gestation sac was found to predict an intrauterine pregnancy with a sensitivity of 42.1% (95% CI 25.3% to 61.0%) and specificity of 96.1% (95% CI 85.2% to 99.1%). The corresponding values for the double decidual sac sign, intradecidual sign, chorionic rim sign and yolk sac are: 81.8% (95% CI 68.1% to 90.4%) and 97.3% (95% CI 76.1% to 99.8%); 66.1% (95% CI 58.9% to 72.8%) and 100% (95% CI 91% to 100%); 79.9% (95% CI 73.0% to 85.7%) and 97.1% (95% CI 89.9% to 99.6%).

CONCLUSION: Visualisation of a gestation sac, double decidual sac sign, intradecidual sign or chorionic rim sign increases the probability of an intrauterine pregnancy but are not as accurate as detection of the yolk sac. The findings were however limited by the small number and poor quality of the studies included and heterogeneity in the index test and reference standard.