The prediction model M6 classifies pregnancy of unknown location (PUL) into a lor-risk or a high-risk group in developing ectopic pregnancy (EP). The aim of this study was to validate the two step M6 model’s ability to classify PUL in French women.
All women with a diagnosis of PUL over a year were included in this single center retrospective study. Patients with a diagnosis of EP at the first consultation of with incomplete data were excluded. For each patient, the M6 model calculator was used to classified them into “high risk of EP” and “low risk of EP” group. The reference standard was the final diagnostic: failed PUL (FPUL), intrauterine pregnancy (IUP) of EP. The statistical measures of the test’s performance were calculated.
Over the period, 255 womens consulted for a PUL, 197 has been included in the study. Final diagnosis were: 94 FPUL (94/197 ; 47,7%), 74 IUP (74/197 ; 37,6%) et 29 EP (29/197 ; 14,7%). The first step of the M6 model classified 16 women in the FPUL group of which 15 (15/16; 93,7%) correctly. The second step of the M6 model classified 181 women: 90 (90/181; 49,7%) in the “high risk of EP” group of which 63 (63/90; 70%) were FPUL/IUP and 27 (27/90; 30%) were EP. 91 (91/181; 50,3%) was classified in the “low risk of EP” group of which 90 (90/91; 98,9%) were FPUL/IUP and 1 (1/91; 1,1%) were EP. EP were correctly classified with sensitivity of 96,4%, negative predictive value of 98,9%, specificity of 58,8% and positive predictive value of 30,0 %.
The prediction model of PUL M6 classified EP in “high risk of EP group” with a sensitivity of 96,4%. It classified 50,3% of PUL in a “low risk of EP” group with a negative predictive value of 98,9%.

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