Inclusion and exclusion criteria of studies
We used “pregnancy of unknown location[Title]” as free text search strings to search all studies diagnosed as PUL in MEDLINE, web of science and Embase at the first visit. All studies exploring PUL outcomes can be included. Other studies related to pregnancy diagnosis were excluded. The eligibility criteria were as follows: (a) the study population was adult patients diagnosed as PUL; (b) the diagnosis of ectopic pregnancy was confirmed by ultrasound, non-visualized treatment (increase in hCG after uterine evacuation) or surgery; and (c) data regarding the true-positive (TP), false-positive (FP), false-negative (FN) and true-negative (TN) rates can be found either directly or indirectly in all studies. All prospective or retrospective randomized controlled trials, case-control studies, cohort studies and observational studies met the inclusion. All reviews, meta-analyses, poster or oral meeting presentation, case reports, letters, responses or comments, and non-English written studies were excluded. The studies before 1984 was excluded, because transvaginal ultrasound had not been a routine test for early pregnancy evaluation before that8.