Background: Parenteral opioids are used for pain relief in labour in many countries throughout the world.
Objectives: To assess the acceptability, effectiveness and safety of different types, doses and modes of administration of parenteral opioids given to women in labour.
Search strategy: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (January 2010) and reference lists of retrieved studies.
Selection criteria: We included randomised controlled trials examining the use of intramuscular or intravenous opioids (including patient controlled analgesia) for women in labour. We looked at studies comparing an opioid with placebo or another opioid.
Data collection and analysis: At least two review authors independently assessed study eligibility, collected data and assessed risk of bias.
Main results: We included 54 studies involving more than 7000 women that compared an opioid with placebo or another opioid administered intramuscularly or intravenously. The 54 studies reported on 27 different comparisons, and for many outcomes only one study contributed data. Overall the evidence was of poor quality regarding the analgesic effect of opioids, satisfaction with analgesia, adverse effects and harm to women and babies. There were few statistically significant results. Many of the studies had small sample sizes, and low statistical power. Overall, findings indicated that parenteral opioids provided some pain relief and moderate satisfaction with analgesia in labour, although up to two-thirds of women who received opioids reported moderate or severe pain and/or poor or moderate pain relief one or two hours after administration. Opioid drugs were associated with maternal nausea, vomiting and drowsiness, although different opioid drugs were associated with different adverse effects. There was no clear evidence of adverse effects of opioids on the newborn. We did not have sufficient evidence to assess which opioid drug provided the best pain relief with the least adverse effects.
Authors' conclusions: Parenteral opioids provide some relief from pain in labour but are associated with adverse effects. Maternal satisfaction with opioid analgesia was largely unreported but appeared moderate at best. We did not examine the effectiveness and safety of parenteral opioids compared with other methods of pain relief in labour and this review needs to be examined alongside related Cochrane reviews. More research is needed to determine which analgesic intervention is most effective, and provides greatest satisfaction to women with acceptable adverse events for mothers and their newborns.