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The Pain of Labour
Simona Labor
Specialist Registrar in Anaesthesia
Simon Maguire
Consultant Anaesthetist, Wythenshawe Hospital, Manchester
summary points
• Labour is an emotional experience and involves both physiological and psychological mechanisms.
• The pain of labour is severe but despite this its memory diminishes with time.
• Labour pain has two components: visceral pain which occurs during the early first stage and the second
stage of childbirth, and somatic pain which occurs during the late first stage and the second stage.
• The pain of labour in the first stage is mediated by T10 to L1 spinal segments, whereas that in the
second stage is carried by T12 to L1, and S2 to S4 spinal segments.
• Pain relief in labour is complex and often challenging without regional analgesia.
• Effective management of labour pain plays a relatively minor role in a woman’s satisfaction with
childbirth.
Introduction The pain of labour has two components: visceral and somatic, and its
anatomy is well documented. The cervix has a central role in both the
The experience of labour is complex and subjective. Several factors first and second stage of labour.
affect a woman’s perception of labour making each experience unique.
However as a consistent finding, labour pain is ranked high on the Visceral pain
pain rating scale when compared to other painful life experiences1. Visceral labour pain occurs during the early first stage and the
The memory of this pain however is short lived and of parturients second stage of childbirth. With each uterine contraction, pressure
who experienced severe pain in labour, 90% found the experience is transmitted to the cervix causing stretching and distension and
satisfactory three months later2. This short term memory may be activating excitatory nocioceptive afferents. These afferents innervate
related to the positive outcome that often occurs at the end of labour. the endocervix and lower segment from T10 – L1.
The pattern of labour pain differs between nulliparous and multiparous
women and it is well documented that pain scores are higher in the
nulliparous compared to the multiparous woman especially if there
has been no antenatal education. Consistent findings also indicate
that nulliparous women on average experience greater sensory pain
during early labour compared to multiparous women3 who seem to
experience more intense pain during the pelvic phase of labour as a
result of sudden stimulation of nociceptors surrounding the vaginal
vault, vulva and perineum4 and rapid descent of the foetus5,6.
Labour pain as well as being unpleasant for the mother, can have
deleterious effects on the foetus (figure 1).
Mechanisms of Labour Pain
Labour is the active process of delivering a foetus and is characterised
by regular, painful uterine contractions which increase in frequency Figure 1
and intensity.
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Table 1 Stages of Labour
1st stage From the establishment of labour (progressive cervical dilatation associated with regular uterine contraction) to full cervical dilatation
2nd stage From full cervical dilatation to delivery of the infant
3rd stage From delivery of the infant to delivery of the placenta
Somatic pain Visceral pain
This occurs in addition to the visceral pain described above, in the Visceral pain is transmitted by small unmyelinated ‘C’ fibres which
late first stage of labour and also in the second stage. It arises due travel with sympathetic fibres and pass through the uterine, cervical
to afferents that innervate the vaginal surface of the cervix, perineum and hypogastric nerve plexuses into the main sympathetic chain.
and vagina and occurs as a result of stretching, distension, ischaemia The pain fibres from the sympathetic chain enter the white rami
and injury (tearing or iatrogenic) of the pelvic floor, perineum and communicantes associated with T10 to L1 spinal nerves and pass
vagina. It manifests during descent of the foetus and during this active via their posterior nerve roots to synapse in the dorsal horn of the
stage, the uterus contracts more intensely in a rhythmic and regular spinal cord. Some fibres cross over at the level of the dorsal horn with
manner. extensive rostral and caudal extension resulting in poorly localised
pain. Chemical mediators involved include bradykinin, leukotrienes,
The intensity of labour pain increases with greater cervical dilatation prostaglandins, serotonin, substance P and lactic acid.
and correlates well with the intensity, duration and frequency of
uterine contractions. The pain of early labour is referred to T10-T12 dermatomes such that
pain is felt in the lower abdomen, sacrum and back. This pain is dull
in character and is not always sensitive to opioid drugs; the response
Pathways of labour pain to opioids depends on the route of administration.
Well documented physiological knowledge provides the basis for Somatic pain
explaining the two components of labour pain: Somatic pain is transmitted by fine, myelinated rapidly transmitting ‘A
delta’ fibres. Transmission occurs via the pudendal nerves and perineal
branches of the posterior cutaneous nerve of the thigh to S2 - S4 nerve
roots. Somatic fibres from the cutaneous branches of the ilioinguinal
and genitofemoral nerves also carry afferent fibres to L1 and L2.
Somatic pain occurs closer to delivery, is sharp in character and
easily localised to the vagina, rectum and perineum. It radiates to the
adjacent dermatomes T10 and L1 and compared to visceral pain, is
more resistant to opioid drugs.
All resulting nerve impulses (visceral and somatic) pass to dorsal
horn cells where they are processed and transmitted to the brain
via the spino-thalamic tract. Transmission to the hypothalamic and
Figure 2a – Visceral Pain limbic systems accounts for the emotional and autonomic responses
associated with pain.
Psychology of labour pain
Labour pain is an emotional experience and presents a psychological
challenge for many parturients. Indeed a recent Cochrane review
concluded that women who had continuous intra-partum support were
less likely to have intra-partum analgesia or to report dissatisfaction.
Other groups have suggested that an underlying anxiety trait can both
result in a higher uptake of epidural analgesia as well as influence
the analgesic effect of the epidural block. There is current interest in
Figure 2b – Somatic pain determining whether the Pain Catastrophizing Score has any influence
on either labour outcome or analgesic uptake.
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Table 2 Management of labour pain
Complementary and alternative therapies for labour Pharmacological analgesia for labour pain
pain
Psychological e.g. hypnosis Inhalational analgesia e.g. entonox, isoflurane, desflurane, sevoflurane
(reduce pain perception)
Physical e.g. transcutaneous electrical nerve stimulation (TENS), Parenteral opioids e.g. pethidine, morphine, diamorphine, fentanyl,
acupuncture remifentanil (reduce pain perception)
Other complimentary e.g. aromatherapy, water immersion Regional analgesia e.g. epidural, combined spinal epidural, continuous
spinal analgesia (reduce pain transmission)
Interestingly there appears to be a circadian variation in labour pain complementary therapies which have minimal side effects and are
perception and one group have demonstrated lower mean daytime easy to administer. Few complementary therapies however are easily
visual analogue pain score compared to nocturnal scores. available or have been subject to proper scientific study. The majority
provide pain relief which is incomplete, unpredictable and inconsistent
Evidence also suggests that attitudes to pain relief in labour depend (TENS, acupuncture), and some simply increase the ability to cope
on personal aspirations, cultural factors and peer group influences.The with labour pain (hypnosis).
ability to cope with pain may be rated as more important than the
level of pain experienced. In one survey, only 9% of women wanted A systematic review of randomised controlled trials comparing
‘the most pain free labour that drugs can give me’. The majority, 67%, water immersion during labour with no immersion concluded that
wanted ‘the minimum quantity of drugs to keep the pain manageable’7. labouring in water in the first stage reduces the use of analgesia and
What seems to be important is that women are more likely to be reported maternal pain, without adverse outcomes on labour duration,
satisfied with pain relief if they felt they had been in control during operative delivery or neonatal outcomes9. These conclusions however
their labour. can only be accepted with caution because the study sample sizes
were small and blinding to the intervention was impossible. Water
immersion may be associated with increased uterine perfusion, shorter
Antenatal education labours and a decreased need for augmentation; the associated feeling
of weightlessness also adds to comfort and allows for easy change
No studies have shown that effective management of labour pain of position during labour. Warm water, as well as inducing muscle
plays a major role in a woman’s satisfaction with childbirth. Antenatal relaxation and reducing anxiety may also decrease the release of
childbirth preparation however has a role in increasing maternal catecholamines and stimulate the release of endorphins.
satisfaction and may reduce pain scores to some extent.
There is conflicting evidence to support the efficacy of TENS in labour.
It is important that anaesthetists are involved with patients antenatally, The majority of trials report it as being ineffective but the evidence for
and in educating midwives and obstetricians. Antenatal education is this is not strong, and in practice many parturients still utilise TENS
also essential when obtaining informed consent from the mother8; in labour. The Cochrane collaboration are currently reviewing all
the aim is to provide good information to facilitate mothers to form randomised controlled trials involving the use of TENS in labour to
realistic expectations and appreciate the limitations of certain methods determine its effectiveness and safety.
of analgesia.
Pharmacological analgesia for labour pain
Inhalational
Management of labour pain
Entonox
The aim of pain relief in labour is to render parturients relatively pain A 50:50 mixture of oxygen and nitrous oxide is the most widely
free whilst still able to participate in the birth experience. Ideally there available inhalational analgesia in the United Kingdom. Despite its
should be no associated side effects or risks to both mother and baby. widespread use, studies have shown that when used in labour for short
In reality, there are several methods of pain relief available but none periods, it is not a potent analgesic but does provide some analgesia
are ideal. and is safe for labouring women and their babies10.
Complementary and alternative therapies for pain management Isoflurane, Desflurane, Sevoflurane
in labour These inhalational gases can be used with or without nitrous oxide
It is not surprising that many mothers try to avoid invasive to improve analgesic efficacy during labour at sub anaesthetic
and pharmacological methods of pain relief in labour and seek concentrations. Compared to entonox, most women prefer sevoflurane,
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and at a concentration of 0.8%, sevoflurane gives significantly better assistance16. In practice the majority of women do not mobilise in
pain relief scores but is associated with more sedation11. labour.
In practice, inhalational gases are not commonly utilised in labour A synergistic effect has been demonstrated between neuraxial opioids
due to technical difficulties in their safe administration, scavenging, and local anaesthetics and the addition of opioids such as fentanyl
requirement of specific vaporisers and concerns about atmospheric to epidural local anaesthetic is associated with improved maternal
pollution. analgesia.The low-dose mixture can be used as a test dose by careful
titration; typically 10 mls 0.1% bupivacaine with 2 mcg/ml fentanyl,
Parenteral opioids contributing to early analgesia in a correctly placed catheter and
allowing early identification of accidental intrathecal injection
Pethidine manifested by rapid onset of analgesia, motor block (especially sacral)
Like entonox, pethidine is readily available and easy to administer. and sympathetic block.
In a survey by the UK National Birthday Trust (NBT), 16% of Maintenance of analgesia in labour is provided by intermittent
women receiving pethidine rated it as ‘helpful’ whereas 25% rated top-up by midwives, by continuous infusion or by use of patient-
it as ‘unhelpful’. Interestingly, midwives rated pethidine higher than controlled epidural analgesia (PCEA). Continuous epidural infusions
parturients, interpreting sedation as analgesia12. The optimal opioid are associated with more motor block than either top-ups or PCEA.
for labour analgesia remains unknown and a systematic review of PCEA in labour is set up with a small background infusion and
the available choices concluded that no other opioid appeared to be tops up that are smaller in volume than those usually administered
better than pethidine in providing pain relief in labour13. In practice, by midwives or anaesthetists, but which can be administered more
pethidine is still the most commonly utilised opioid as it can be easily often. It results in satisfactory analgesia with reduced overall dose of
administered by midwives. The effects of systemic opioids in labour bupivacaine and fentanyl.
are predominantly sedative rather than analgesic14; other opioids
when used in labour are usually administered as patient controlled Labour epidurals are associated with an increase in the duration of the
analgesia. second stage and an increased risk of instrumental vaginal delivery.
They are also associated with an increased need for stimulation of labour
Remifentanil contractions and may cause reduction in maternal blood pressure, and
This is increasingly being used due to its fast onset and short duration fever.They are the commonest cause of intrapartum pyrexia which
of action. A typical bolus dose of 0.25 – 0.5 µg/kg with a lockout is strongly associated with poor neonatal outcome in the form of
period of 1 – 2 minutes is currently being used. A small double blind neonatal encephalopathy and cerebral palsy. The exact mechanism is
crossover study has suggested than intravenous remifentanil when unknown but it is thought that an increased temperature of tissues
compared to entonox provides better pain relief15. increases their metabolic rate and therefore their oxygen requirements,
resulting in cerebral palsy.
The efficacy of systemic opioids for labour analgesia is limited and
undoubtedly inferior to regional analgesia, however there are often The sympathetic blockade accompanying low-dose epidural top-ups
times when regional analgesia is not appropriate and alternative is slow in onset and seldom extensive. Maternal hypotension in these
analgesia is essential. circumstances is usually associated with aorto-caval compression.
Regional analgesia Immediate serious complications of epidural analgesia include: massive
misplaced injection intravascularly, intrathecally, or subdurally, high
Epidural or total spinal block (rare), hypotension, and local anaesthetic induced
Epidural analgesia is thought to be the most effective method of convulsions and cardiac arrest (rare). Delayed complications include
providing pain relief in labour and involves injecting local anaesthetic post dural puncture headache, transient backache, urinary retention,
close to the nerves that transmit pain. It also gives the option of epidural haematoma, abscess or meningitis (rare) and permanent
providing regional anaesthesia for obstetric interventions such as neurological deficit (rare). The majority of neurological injuries in this
forceps delivery and caesarean sections, and obese and other parturients setting are not as a result of neuraxial analgesia but are intrinsic to
who are at risk of obstetric interventions particularly benefit from an labour and delivery.
early epidural.
The amide local anaesthetic, levobupivacaine, is less cardiotoxic than
Low –dose local anaesthetic and opioid mixtures; typically 10 – 15 racemic bupivacaine when given intravenously. However, cardiotoxic
mls 0.1% bupivacaine with 2mcg/ml fentanyl are currently in use in doses of bupivacaine are unlikely to be reached if low-dose infusions
most delivery units, however some units still use higher concentrations or top-ups are used. 20% lipid emulsion is now widely available as
of bupivacaine for labour analgesia.Low-dose mixtures are thought treatment for cardiac arrest secondary to overdose of these long acting
to provide excellent analgesia while preserving motor function with local anaesthetics17.
the mother more likely to mobilise during labour or deliver without
reviews in pain
Vo l . 2 , N o . 2 , D e c e m b e r 2 0 0 8 19
Combined Spinal Epidural (CSE) 7. Green JM, Coupland V, Kitzinger JV. Expectations, Experiences,
This involves an initial injection of a low dose of local anaesthetic and Psychological Outcomes of Childbirth: A Prospective Study
and opioid (e.g. bupivacaine 2.5mg + fentanyl 15 –25mcg) into the of 825 Women Birth 2007; 17: 15
subarachnoid space followed by an epidural top-up. This method is
thought to provide more rapid and complete analgesia with less motor 8. The Association of Anaesthetists of Great Britain and Ireland.
block compared with the conventional epidural method18. In practice, Guidelines on Consent for Anaesthesia. Revised Edition 2006
traditional epidurals are performed far more frequently for labour
analgesia than CSEs. There appears to be little basis for offering CSEs 9. Cluett ER, Nikodem VC, McCandlish RE, Burns EE. Immersion
over epidurals in labour and it is debatable whether breaching the dura in water in pregnancy, labour and birth. Cochrane Database
can ever be justified. of Systematic Reviews 2002, Issue 2. Art. No.: CD00011.
DOI:10.1002/14651858.CD000111.pub2
Evidence shows no difference in retrospective maternal satisfaction,
ability to mobilise and obstetric and neonatal outcome. Many units 10. Rosen M. Nitrous oxide for pain relief of labor pain: a systematic
reserve this technique for those in rapidly advancing labour when review. Am J Obstet Gynecol 2002; 186: S110-26
analgesia, particularly sacral is needed in the second stage of labour
and for the multiparous parturient who had an ineffective epidural 11. Yeo ST, Holdcroft A, Yentis SM, et al. Sevoflurane compared with
on a previous occasion.Perceived risks of the CSE technique include Entonox for labour analgesia. Br J Anaesth 2007; 98: 110-15
increased incidence of post-dural puncture headache, meningitis and
epidural catheter migration through the dural hole. 12. Chamberlain G, Wraight A, Steer P, eds. Pain and its relief in
childbirth: the results of a national survey conducted by the
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may be inherently more dangerous than the other two techniques. 15. Volmanen P, Akural E, Raudaskoski T, Ohtonen, P. Alahuhta, S.
Comparison of remifentanil and nitrous oxide in labour analgesia.
Acta Anaesthesiol Scand 2005; 49: 453-8
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Dr S Maguire
6. Ranta P, Jouppila R. The intensity of labour pain in grand
multiparas. Acta Obstet Gynecol Scand 1996; 75: 250-4 Consultant Anaesthetist
Wythenshawe Hospital - Southmoor Road Wythenshawe
Greater Manchester, M23 9LT
email: simonmacguire@doctors.org.uk
