Introduction
Normal labour
Normal labour is defined as painful uterine contractions accompanied by effacement and dilatation of the cervix that finally leads to delivery of the newborn, placenta, and membranes.
For management purposes, labour is divided into three stages:1. The first stage is defined as the duration of observed onset of painful contractions that is associated with cervical changes to full dilatation. The first stage is conventionally divided into a latent phase and an active phase. The latent phase is characterized by progressive cervical effacement and early cervical dilatation. This may be accompanied by mild, irregular uterine contractions and may occur insidiously before the woman presents to the delivery suite. A fully effaced cervix signals the end of the latent phase. There is less agreement on the cervical dilatation at which the latent phase ends and the active phase begins. Traditionally, this was thought to be at 3-4 cm but a limit of 6 cm has been more recently proposed (1). This observation established the rate of cervical dilatation at various points in labour in nulliparae as set out in Table 26.1.
This and earlier observations identify an active phase, characterized by more rapid cervical dilatation that culminates in full dilatation, commencing at 6 cm. Following the more recent observations, many centres in the United States consider the active phase to commence at 6 cm cervical dilatation. Prospective studies are needed to adopt such an approach into routine clinical practice.
2. The second stage is the period from full dilatation of the cervix to delivery of the fetus. In a nullipara, it is considered prolonged if the diagnosed second stage lasts more than 3 hours in a woman who has received regional anaesthesia and 2 hours in the absence of regional anaesthesia. Thresholds of 2 hours and 1 hour are usually applied in multiparous women in the presence and absence of regional anaesthesia, respectively.
These thresholds are somewhat arbitrary in that they refer to the diagnosed duration of the second stage. There is a popular view that, with modern methods of fetal surveillance, the second stage can be prolonged beyond these limits without adverse effects.3. The third stage is the period from delivery of the fetus to complete delivery of the placenta and membranes. Expectant and active management of the third stage are possible. Active management is shown to be beneficial as discussed further in this chapter.
The mechanism of labour
The mechanism of labour involves changes in the position of the fetal presenting part during labour and is described in relation to a vertex presentation. The following discrete steps are described:
1. Engagement.
2. Descent.
3. Flexion.
4. Internal rotation of the fetal head from an occipitotransverse to occipitoanterior position. This is termed internal rotation because it occurs within the pelvis.
5. Extension is the mechanism by which the fetal head is delivered.
6. Restitution—the rotation of the head to be in alignment with the shoulders.
7. External rotation of the fetal head outside the pelvis with rotation of the fetal shoulders within the pelvis. This is termed external rotation as it is visible to birth attendants, the fetal head having been delivered.
8. Expulsion of the rest of the fetus.
The partogram
A partogram is a continuous, pictorial/graphical overview of labour on which clinicians record labour observations. Modern partograms have three distinct sections to record details with regard to maternal condition, fetal condition, and labour progress. Friedman was the first obstetrician to describe the progress of normal labour graphically when he studied 500 primigravid women in labour (2). By plotting the progress of cervical dilatation in centimetres against duration of labour, he described a sigmoid- or ‘S’-shaped curve which became known as the cervicograph. Philpott devised a partogram (3) based on Friedman’s cervicograph which he used for clinical benefit in Zimbabwe (then Rhodesia). Philpott’s partogram had an alert
Table 26.1 Rate of cervical dilatation in spontaneously labouring nulliparae
| Cervical dilatation (cm) | Duration (hours) | ||
| From | ∣2°______ I | I Median | 95th centile |
line which represented the mean rate of dilatation of the slowest 10% of primigravid women.
An action line was plotted parallel and 4 hours to the right of the alert line (Figure 26.1 a). This partogram was an attempt to utilize midwives efficiently in a hospital where doctors were in short supply. The clinical protocol stipulated that women would be transferred from a peripheral unit to a central unit if progress of cervical dilatation crossed the alert line. If progress was further slowed such that it crossed the action line, an intervention such as amniotomy and/or oxytocin infusion for augmentation of labour would be introduced. More simplified versions of the partogram have been proposed including a version by the World Health Organization (WHO) (Figure 26.1b). These simplified versions omit a latent phase on the basis that women in spontaneous labour usually present in the active phase of labour. Other versions may omit action and alert lines (Figure 26.2), allowing the obstetrician to draw these when required. Another modification is the active management of labour (AML) partogram used by the National Maternity Hospital in Dublin, Ireland (Figure 26.3). The AML partogram similarly dispenses with a latent phase and places emphasis on establishing full effacement of the cervix as the sine qua non of labour rather than the degree of cervical dilatation. There is evidence that these simplified versions are preferred by clinicians.Research into whether a partogram reduces the caesarean section rate or improves maternal and neonatal outcomes has largely yielded divided results. A large multicentre trial showed a reduction in prolonged labours, caesarean sections in labour, and intrapartum stillbirths when the WHO partogram was utilized in units not previously using a partogram (4). Conversely, a Cochrane review showed no differences in clinical outcomes with or without partogram use (5).
Other modifications in the partogram include using a 2-hour or 3-hour action line as opposed to the original 4-hour action line. Some authors propose an alert line alone without an action line. These modifications also do not appear to alter clinical outcomes. Using an action line with a shorter duration results in more women receiving interventions such as amniotomy or augmentation with oxytocin (5).
Despite the lack of conclusive scientific evidence to support its use, it is widely accepted that the partogram is a useful tool in the management of labour. The pictorial nature of the partogram allows for easy identification of labours which are not progressing normally. The partogram also allows for systematic documentation of labour details as well as maternal and fetal parameters which may minimize omissions.
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