• vaginal delivery
• obstetric intervention
• time of day

The frequency of use of commonly performed obstetric procedures to assist in vaginal delivery has been shown to vary according to characteristics of both the patient and provider, independently of clinical indications for intervention.^1–5 This variation in procedure use according to “non-medical” factors is worthy of attention, as it raises the spectre of unnecessary intervention that increases the cost of maternity care, and possibly the risks of adverse maternal or neonatal outcomes as well. Mounting evidence of the additional maternal and neonatal morbidity associated with frequent episiotomy use ⁶ and operative vaginal delivery,^7,8 in particular, underscores the need to examine the extent, causes and consequences of the unnecessary use of these and other obstetrical interventions to assist in vaginal delivery.

Obstetrical procedures may be overused or misused, at least in part, for the purposes of convenience—that is, as a way for doctors and hospitals to control patient flow or manage time more efficiently.^1,9–13 While there is some empirical evidence for this “convenience” hypothesis with regard to caesarean section practices,^11,13 there is little such evidence where obstetric procedures to assist in vaginal delivery are concerned. We explored the extent to which “convenience” factors may be influencing the use of obstetric procedures other than caesarean section, for a geographically defined study population of women at relatively low risk for obstetric intervention. Specifically, the objective of the study was to document any time of day variation associated with labour augmentation, episiotomy, or instrumental delivery—variation that may indicate more willingness to perform these procedures during times when providers may be under additional pressures to influence (that is, …