Fig. 1

A conceptual framework in selecting compatible subjects for comparison. The intervention group (preventive induction) and expectant management (ongoing pregnancies as control group) at a particular gestational age (e.g., 37 weeks) were further divided based on the propensity score for preventive induction. Propensity score levels are divided based on the propensity scores in the preventive induction group (<25th, 25th–49th, 50th–74th, and ≥ 75th percentiles). These cut-off points were then applied to the expectant management group. 1 = least likely to have preventive induction; 4 = most likely to have preventive induction. Comparisons were made between the intervention and control groups at the corresponding propensity score level