Randomised controlled trials (RCTs), prospective and retrospective cohort studies that reported on the effects of early epidural analgesia (3cm or less) versus late epidural analgesia (at least 4cm) on mode of delivery were eligible for inclusion. Nulliparous women with a gestational age of at least 36 weeks, spontaneous or induced labour, with a singleton in vertex presentation were included. The primary outcome rate of caesarian or instrumental vaginal deliveries.
Four of the included studies reported only on women in spontaneous labour. The other studies included a mixture of spontaneous and induced labour. Most women who received late epidural analgesia received systemic opioids before the epidural (drugs and doses varied). Other analgesics were used (doses varied). No further patient characteristics were reported.
Two reviewers independently screened and selected studies for inclusion. Disagreements were resolved with a third reviewer where necessary.