Pain during labour is normal and its management is influenced by an interaction between a woman's mental and emotional state and the physiological changes that occur during labour. The use of pain-relieving drugs during labour is now part of standard care in many countries throughout the world. In recent years, many women in Western countries have chosen to have epidural analgesia to relieve pain. However, some women prefer not to have an epidural, or in some settings an epidural is not available. In many maternity units intramuscular injections of opioid drugs are widely used for pain relief in labour and options for intravenous infusions may also be available. The opioid drugs used include pethidine (also known as meperidine or demerol), diamorphine, nalbuphine, butorphanol, meptazinol, pentazocine, fentanyl and tramadol, and are relatively inexpensive. It is not clear how effective these drugs are, which opioid is best, and how unpleasant side effects (such as vomiting or sleepiness) or harm to women or their babies can be avoided.
We included 57 randomised controlled trials involving more than 7000 women that compared an opioid with placebo, another opioid or transcutaneous electrical nerve stimulation (TENS). Overall, our findings indicated that opioids provided some pain relief during labour, although substantial proportions of women still reported moderate or severe pain. Opioid drugs were associated with nausea, vomiting and drowsiness, and different types of opioids were associated with different side effects. There was no clear evidence of adverse effects of opioids on the newborn. Maternal satisfaction with opioid analgesia was largely unreported but appeared moderate. We did not have sufficient evidence to assess which opioid drug women were most satisfied with, or which provided the best pain relief with the least side effects for mothers and babies.
In this review the 57 studies reported on 29 different comparisons, and for many outcomes only one study contributed data. We did not examine the effectiveness and safety of intramuscular or intravenous (parenteral) opioids compared with other pharmacological methods of pain relief in labour (such as epidural analgesia) and this review needs to be examined alongside related Cochrane reviews. As parenteral opioid drugs are so widely used it is important that more research is carried out so that women can make informed choices about these forms of pain relief.