The effect of epidurals on the normal progress of labour
Epidurals have been used in labour for four decades. A valid criticism of epidurals during this time and an issue which has been the focus of much research is the effect which epidurals may have on the ‘normal’ progress of labour. Epidurals have been implicated in causing a prolongation of the duration of labour, an increase in instrumental deliveries (forceps) and an increase in caesarean section.
Prolonged labours can be associated with fetal distress and maternal exhaustion. When these conditions are present it is often considered important to speed up the delivery of the fetus. This can be done by an ‘assisted’ delivery with forceps or vacuum suction (ventouse), or by an ‘operative’ delivery, by caesarean section. Until recently, one of these would also have been performed if the labour was prolonged beyond conventionally accepted limits (for instance; 2 hours second stage) even when no signs of fetal or maternal distress were present.
Many women have described disappointment and a sense of failure as a result of having had a forceps delivery because they feel that their ability to participate in the birth was diminished.
Forceps deliveries have been associated with brain haemorrhage and birth asphyxia in the infant. Several points should be emphasised however. Firstly, that these problems have mainly occurred in severely premature and low-birth-weight babies (because the supportive tissue of the brain is under-developed) and in other high risk infants including twins and those presenting breech. Furthermore, they are associated with high or mid-cavity rotational forceps. This means that the forceps are applied to the infant’s head when it is still fairly high in the pelvis and may involve more traction. Nowadays, these are performed much less frequently: forceps deliveries in present times are most likely to be low, outlet forceps, or ventouse suction which are not associated with serious problems like those described. Most importantly however, much of the data available on this subject is dated and does not take into account modern obstetric and anaesthetic practices. This is particularly relevant to the practise of epidural analgesia.
Whilst the problems associated with ‘interventional’ deliveries should in no way be overlooked, it is important to appreciate that the vastly improved safety during childbirth for both mother and infant alike, which has been witnessed this century, comes as a result of modern practices such as these. It is reasonable to predict that most women would willingly accept the need for this type of delivery if complications with their labour had arisen as a result of unforseen circumstances (for instance; the fetal head fitting tightly in the birth canal). It is however, quite understandable that they would feel rather less accepting of a forceps delivery if it were needed simply as a result of the presence of an epidural.
The effect of epidurals which has been held most responsible for the observed association with forceps deliveries is weakness of the pelvic floor muscles and excessive numbness of the birth canal which may impair the mother’s ability to coordinate her efforts with the bearing down reflex.
The second (delivery or pushing) stage of labour begins at that time when the cervix has reached full dilatation (10 cm) and the head has descended within the pelvis to an appropriate station. At this point in time ‘involuntary’ activity of the pelvic floor muscles occurs in synchrony with uterine contractions. This is called the bearing down reflex and is often felt as a strong desire to open one’s bowels. These events act to push the fetal head through the open cervix and birth canal toward the vaginal opening (perineum). During this time ‘voluntary’ contracting of the abdominal wall and pelvic floor muscles by the mother will contribute to the effectiveness of the delivery.
In order to achieve a ‘spontaneous vaginal delivery’, the fetal head must negotiate the changing diameter of the birth canal as it descends through it. It does this by assuming a series of changes in head position in the following sequence: lateral flexion (head tilts to the side); internal rotation (the head rotates 90 degrees so that the back of the head, or occiput, faces forward); extension (head tilts back); restitution (the delivered head rotates back to its original position. These manoeuvres may fail to occur or occur slowly if either the uterus or the pelvic floor muscles are not contracting well. The fetus may become distressed if this stage is prolonged and until recently many centres maintained a policy of performing forceps deliveries if it exceeded 2 hours. More recently, investigators have demonstrated that a longer second stage is not associated with fetal distress as long as the fetus is monitored and the mother is well hydrated and has good pain relief.
The effect of epidurals in the progress of labour has been the subject of both scrutiny and applied research for some time. Unfortunately, so many ‘variables’ have existed that few of the studies are able to be compared to each other in a meaningful way. Whilst it is tempting to be impressed by the findings of a new research study, it is extremely unlikely that any one study will provide the exact answer to any question raised. A review of all the research which has been performed on an area like epidurals often reveals a lot of conflicting results. An even closer look usually reveals differences between the subjects (women in labour), the practices ( high concentration versus low concentration epidurals) and the criteria for deciding the outcomes (no differentiation between different types of forceps deliveries or different thresholds for performing them). It is possible to ‘select’ out studies which suit one’s point of view but this is a misuse of research.
With respect to research into epidurals three main problems have existed. Because women usually request epidurals very few studies have had random allocation of labouring women into ‘epidural’ versus ‘no epidural’ groups. Hence the question remains that women who request epidurals may experience labours which are more painful, more prolonged and intrinsically more likely to require interventions like forceps delivery. The request for an epidural may be a symptom of the complication rather than the cause of it!. Secondly, anaesthesia practice has changed so dramatically such that findings from twenty years ago are sometimes not relevant to current practices. Finally, the practice of obstetrics can vary greatly between units and obstetricians with respect to the ‘indications’ for performing instrumental deliveries. In order to be able to come to clear conclusions about the effects of epidural analgesia on the progress of labour and the likelihood of deliveries such as forceps and caesarean section, studies would have to involve thousands of women who are all experiencing similar labours, receiving similar types of epidural pain relief and whose labours were being managed along similar medical guidelines.
Nevertheless, three firm conclusions can be drawn about the effects of epidural analgesia on the progress of labour:
1. Overall, epidurals ‘per se’ are associated with an increased incidence of forceps deliveries but this effect is reduced by the use of progressively weaker concentrations of local anaesthetic agents and the addition of opioids. Low-concentration local anaesthetic and opioid solutions appear only associated with low and outlet forceps and ventouse suction.
2. Epidurals are associated with a prolongation of the second stage but this is not associated with any risk to the fetus in a properly managed labour.
3. There is no acceptable evidence that associates epidurals with an increased incidence of caesarean section.
Epidurals have the capacity to prolong the second stage of labour and as a result have been associated with a higher forceps delivery rate. In high concentrations given close to second stage they may increase the likelihood of midcavity forceps. The administration of high concentration local anaesthetic into the epidural is not common routine practice nowadays. Situations in which this approach might be employed include the following:
Several practices have developed which endeavour to preserve pelvic muscle strength during second stage. They include:
The incorporation of these practices into epidural analgesia have been responsible for many of the improvements which have occurred during recent years. Epidurals can provide excellent pain relief particularly during the longest stage of labour (stage 1) but without many of the side effects seen previously (eg; leg numbness) Unfortunately, the adoption of these practices also explain why epidurals may not provide good pain relief during the actual delivery
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