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Pain relief in labour
Introduction
Although there is an acceptance, to a degree, that labour is a painful experience, we must guard against the inevitability that labour should be painful. Mothers, especially primigravidae, find it difficult to conceptualize the amount of pain they may experience or their ability to cope with it, until they are in established labour. Mothers may choose to suffer some pain, but the extent to which the mother should experience pain should ideally be agreed, mainly by the mother but in consultation with a midwife and/or obstetrician and/or anaesthetist.
The pain of labour can be severe. It is a complex mix of physiological, psychological and emotional factors and can be difficult to treat. Many different forms of analgesia have been suggested and each has varying efficacies, risk profiles and potential complications.
Pain is unpleasant for the mother, although there is often some amnesia, which can positively influence its perception in retrospect. It is also recognized that the childbirth experience is influenced by maternal expectations and preparation and by the severity of pain in labour.
Factors influencing pain
The severity of labour pain can vary, depending on obstetric, psychological and emotional factors.
Pain scores have been shown to be higher in primigravid women than in multiparous women, especially if they have not had any antenatal preparation. Reports have also shown that primigravid women generally experience more sensory pain during early labour compared with multiparous women, who experience more intense pain much later in labour, as a result of rapid descent of the fetus.
Long labours are perceived as being more painful. Labour is also reported to be more painful with fetal malposition and, in particular, a woman whose baby is occipitoposterior may experience continuous backache and a prolonged labour.
Physiology of labour pain
There are two components to the pain of labour: visceral (relating to an organ, i.e. the uterus) and somatic (relating to other tissues).
Visceral labour pain occurs during the first stage of childbirth and is due to progressive mechanical dilatation of the cervix, distension of the lower uterine segment and contraction of the uterine muscles. Labour pain may also be as result of the myometrial and cervical ischaemia that occurs during contractions. Severity of this pain mirrors the duration and intensity of contractions. Visceral pain is transmitted by small unmyelinated ‘C’ fibres, which travel with sympathetic fibres and pass through the uterine, cervical and hypogastric nerve plexuses into the main sympathetic chain. The pain fibres from the sympathetic chain then enter the white rami communicantes associated with the T10 to L1 spinal nerves and pass via their posterior nerve roots to synapse in the dorsal horn of the spinal cord. Chemical mediators involved in this pain transmission include bradykinin, leukotrienes, prostaglandins, serotonin, substance P and lactic acid. This pain is dull in character and is sensitive to opioid drugs.
Somatic labour pain occurs during the late first stage and the second stage of labour and is due to stretching and distension of the pelvic floor, perineum and vagina. It occurs as a result of descent of the fetus, and during this stage of labour, the uterus contracts more intensely in a rhythmic and regular manner. 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 to S4 nerve roots. Somatic fibres from the cutaneous branches of the ilioinguinal and genitofemoral nerves also carry afferent fibres to L1 and, to some degree, L2.
All resulting nerve impulses (visceral and somatic) pass to dorsal horn cells and finally to the brain via the spinothalamic tract. Direct pressure of the fetus on the lumbosacral plexus also results in neuropathic pain during labour.
Psychology of labour pain
Maternal control makes labour a more positive experience. Attitudes to pain and pain relief in labour depend on personal aspirations, expectations, cultural factors, learned behaviours, peer group influences, desirability of the pregnancy, previous experiences of pain, pre-existing anxiety or depression, and preparation, education and communication.
Methods of pain relief
Non-pharmacological methods
Maternal support
Psychological support is extremely valuable and allows pharmacological intervention to be minimized. With continuous 1:1 support in labour mothers need less analgesia, are more likely to have a vaginal delivery, and are more satisfied with their labour. The supporting person does not need to be the mother’s partner or a midwife, and indeed it may be more useful if they are not part of the mother’s social network at all.
