Studies report an increased risk of maternal and fetal adverse side effects when combined spinal-epidural, rather than standard epidural, analgesia is provided for labour and delivery. Intrathecal opioids used with local anaesthetic in combined spinal-epidural analgesia may be a cause. It is not known whether this is due to the addition of opioid to local anaesthetic in the intrathecal space only or due to concomitant administration into the intrathecal and epidural spaces.