Timing of induction of labor and association with nighttime delivery: a retrospective cohort

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To assess the risk of nighttime delivery associated with timing and method of labor induction.


We reviewed records of 692 patients undergoing full, late or post-term labor induction at two large hospitals. Primary independent variables were start time (morning or evening) and method (prostaglandin or oxytocin). Relative risk was assessed for the primary outcome of nighttime delivery.


Two hundred and ninety-seven (42.9%) patients experienced nighttime delivery. The relative risk of nighttime delivery adjusted for age in multiparous women using oxytocin in the morning compared with oxytocin inductions in the evening was 0.31 (95% confidence interval (CI): 0.22 to 0.45). Among nulliparous women in the same group, the adjusted relative risk was 0.65 (95% CI: 0.36 to 1.19). For prostaglandin inductions, there was no difference in the risk of nighttime delivery based on timing of the induction in the evening (relative risk: 0.89; 95% CI: 0.71 to 1.10).


The method used and the time at which induction is started affect risk of nighttime delivery. For multiparous patients receiving oxytocin, morning induction carries lower risk of nighttime delivery. For prostaglandins, timing of initiation did not affect risk of nighttime delivery.

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