You are planning a cohort study of the possible influence of elective induction of labor at 39 weeks’ gestation on the risk of several adverse maternal and fetal outcomes, including the need for cesarean section.

As a basis for comparison to the women receiving elective induction, you are considering two possibilities:

(a) Women who delivered a child at 39 weeks who went into labor spontaneously and (like the women who were electively induced) did not have any indication for induction (e.g., preeclampsia, gestational diabetes)

(b) Women who at 39 weeks had not yet delivered and (as of that time) had no indication for induction.