Study selection
By searching MEDLINE, SCIE and EMBASE, 219 articles were found after
eliminating duplicate citations.
After reading the full text, ninety-one citations were retained. Next,
the following citations were excluded: thirty-nine were
not intended to describe and predict
the outcome of PUL, twelve had insufficient data integrity to support
the analysis, nine did not have high-risk category (i.e., EP or PPUL),
and two did not propose specific prediction protocols. The flow of paper
retrieval is summarized in figure 1. As a result, twenty nine studies
were included.7, 10-37 Among them, three used M1
model, four used single progesterone threshold protocol, two used M6
model, nine used M4 model, one used P1 model, five used hCG ratio (hCG
48 hours / hCG at 0 hours) protocol, two used the two steps method, the
combination of progesterone and hCG threshold protocol, seven used
single hCG cut-off protocol, one used FFN protocol, one used ultrasound
imaging results and hCG, one used ultrasound imaging results and one
used Activin-A protocol.