Attributes and levels Mean coefficient (95%CI) Standard deviation (95% CI) Constant# 3.65 (1.41 to 5.89)* 1.56 (0.34 to 2.78)* Cervix length measurement              No measurement (omitted) 1.64 (1.10 to 2.18)* 1.69 (0.29 to 3.19)*          Abdominal -0.77 (-1.03 to -0.51)* 0.38 (-0.03 to 0.79) Vaginal -0.87 (-1.39 to -0.35)* 0.63 (0.05 to 1.21)* Progesterone administration                No (omitted) 0.71 (0.63 to 0.99) 0.21 (0.03 to 0.39)*            Oral -0.21 (-0.26 to -0.16)* 0.05 (0.00 to 0.09)            Vaginal -0.49 (-0.70 to -0.28)* 0.12 (0.01 to 0.23)* Short-term complication rate (per 1%) -0.16 (-0.24 to -0.08)* 0.04 (-0.06 to 0.15) Long-term complication rate (per 1%) -0.37 (-0.55 to -0.19)* 0.12 (-0.05 to 0.29) Number of responses 6624   Number of respondents 138   Log likelihood -874   AIC 91   BIC 97   #Alternative specific constant for no treatment (the opt-out) *P<0.01

Table 3: Four attributes were used for discrete choice experiment to assess women’s preferences for. The negative sign of the coefficient reflects a negative effect on utility, the value indicates the relative importance of the attribute to total relative utility. A statistically significant coefficient indicates that respondents considered that attribute important.