A large number of pregnant women are assessed as being ‘low-risk’ and are predicted to have a normal labour, but the diagnosis of normal labour is retrospective.
The parameters for normal labour are:
• Contractions once in every 3 minutes, lasting 45 seconds
• Progressive dilatation of the cervix
• Progressive descent of the presenting part
• Vertex presentation with the head flexed and the occiput anterior
• Labour not lasting less than 4 hours (precipitous) or longer than 18 hours (prolonged)
• Delivery of a live healthy baby
• Delivery of a complete placenta and membranes
• No complications
A low-risk mother would traditionally have midwife-led care. Low-risk multiparous women may choose to give birth at home or in a midwifery-led unit, where the rate of intervention is lower and neonatal outcome the same. There is a small increase (of about 4 per 1000 births) in adverse neonatal outcomes for low-risk nulliparous women who choose a home birth.
A labour record is kept to measure and record the vital signs of the mother and fetus, together with the progress of labour. It also serves as a record of events should an adverse outcome occur, especially if there is subsequent medicolegal involvement (see Chapter 170, Medicolegal aspects; Chapter 171, Record keeping). A list of items recorded would normally include:
• Fetal heart rate every 15 minutes
• Cervical dilatation at least every 4 hours
• Descent of the presenting part
• Colour of the liquor
• Fetal pH if relevant
• Amount of oxytocics given
• Strength and frequency of uterine contractions
• All drugs administered, including those for an epidural
• Maternal blood pressure, pulse rate and temperature
• Urine volume and analysis for ketones, protein or glucose
• Fluid input
The most commonly used means of charting the progress of labour is the partogram, which presents the data in a graphical form. ‘Normal’ curves may be printed on the partogram, obtained from large numbers of healthy primigravidae and multigravidae, against which it is easier to assess the progress of labour. An example of a partogram is shown in Figure 19.1.
First stage of labour
During the latent phase, the cervix effaces and then cervical dilatation begins. This may be associated with painful contractions. A woman is said to be in established labour once regular contractions occur and there is progressive cervical dilatation from 4 cm. The rate of cervical dilatation should be around 0.5 cm per hour for a primiparous woman and 1 cm per hour for a multigravid woman.
It is standard practice to perform a vaginal examination every 4 hours to assess the dilatation of the cervix, or more frequently if there is cause for concern. The fetal heart may be monitored intermittently by auscultation using Pinard’s stethoscope or by cardi- otocographic monitoring (see Chapter 20, Intrapartum fetal monitoring). The cardiotocogram (CTG) is recorded either intermittently or continuously depending on the condition of the fetus. Continuous recording of fetal heart rate may be done using either an abdominal transducer or a clip applied to the fetal head. Radiotelemetry is available in some units, and this allows the woman to be mobile while her baby is monitored. Uterine contractions may be monitored externally by an abdominal transducer or internally by an intrauterine catheter. The fetal heart rate and the uterine contractions are recorded together.
Second stage of labour
The second stage of labour commences at full dilatation of the cervix and terminates at the delivery of the baby.
At full dilatation of the cervix, the character of the contractions changes and they are usually, but not invariably, accompanied by a strong urge to push. In normal labour, there is an increase in circulating oxytocin secondary to Ferguson’s reflex, with consequent increased strength of uterine contractions at full dilatation. Higher-dose epidural analgesia is thought to diminish the effect of this reflex.
The second stage of labour can be divided into passive and active stages, and this is particularly relevant when epidural analgesia is used. With epidural analgesia, especially using older, higher-dose techniques, the labouring woman may not have the normal sensation at the start of the second stage of labour. Therefore, the active stage of pushing should only commence when the vertex is visible or the woman has a strong urge to push. In normal labour, the active stage usually commences at full dilatation. Traditionally, the second stage is limited to 2 hours because of the risk of fetal acidosis; up to 3 hours is often allowed in the presence of epidural analgesia, in recognition of the slower descent of the fetal head. It is difficult for a woman to push efficiently for more than 1 hour, and after this time fetal acidosis is felt to be more likely. If there is not good progress, the advice of the obstetrician should be sought. Intramuscular oxytocics are given to hasten the delivery of the placenta and to stimulate uterine contraction: 10 U oxytocin (Syntocinon) intramuscularly after delivery of the anterior shoulder (so as not to exacerbate shoulder dystocia if present) is now considered the drug of choice, as it is associated with fewer side effects than oxytocin/ergometrine (Syntometrine).
Figure 19.1 Example of a partogram for assessing and recording the progress of labour. Reproduced with permission from Perinatal Institute, Birth Notes Version 17.1 (May 2017). © Perinatal Institute.
Third stage of labour
The third stage of labour is the complete delivery of the placenta and membranes and the contraction of the uterus. It is usually managed actively by administering an oxytocic as above, but it may also be managed physiologically without oxytocics. This may prolong the third stage and increase the risk of postpartum haemorrhage.
During the third stage of labour there is a major redistribution of (and increase in) maternal circulating blood volume. This is potentially dangerous to those women who have cardiac disease, who may be precipitated into heart failure immediately postpartum.
Figure 19.1 (cont.)
Departure from a normal labour
Certain signs may trigger departure from a normal labour and/or necessitate transfer to obstetric-led care:
• Maternal tachycardia (> 120 beats/minute on two occasions 30 minutes apart)
• Maternal hypertension (diastolic blood pressure (DBP) > 110 mmHg or systolic blood pressure (SBP) > 160 mmHg, or two consecutive readings of DBP > 90 mmHg or SBP > 140 mmHg)
• Proteinuria (2+ on urinalysis) and a single reading of raised blood pressure of 140/ 90 mmHg
• Pyrexia of 38 °C on a single reading, or 37.5 °C on two consecutive readings 1 hour apart
• Vaginal blood loss other than a show
• Rupture of membranes more than 24 hours before the onset of established labour
• Significant meconium
• Abnormal presentation or lie
• A high (> 4/5 palpable) or free-floating head in a primiparous woman
• Anhydramnios or polyhydramnios
• Fetal heart rate < 110 or > 160 beats/minute
• A fetal heart rate deceleration
• Reduced fetal movements reported in the last 24 hours
• A delay in the first or second stage of labour
• A retained placenta or a third/fourth-degree tear
• A request for regional analgesia; this does not in itself confer ‘abnormality’ to an otherwise uncomplicated labour, but may require transfer to obstetric-led care depending on local policy.
Key points
• Normal labour can be anticipated but can only be diagnosed after delivery.
• Routine recording of labour is a standard of care in maternity units.
• The partogram is used to chart labour, and for reference should a bad outcome or legal proceedings occur.
• The first stage comprises cervical effacement and dilatation.
• During the second stage, the baby passes through the birth canal.
• The placenta and membranes are delivered during the third stage.
Further reading
Ferguson E, Owen P. The second stage of labour. Hosp Med 2003; 64: 210-13.
National Institute for Health and Care Excellence. Intrapartum Care for Healthy Women and Babies. Clinical Guideline 190. London: NICE, 2014 (updated 2017). www.nice.org.uk/ guidance/cg190 (accessed December 2018).
Steer P, Flint C. Physiology and management of normal labour. BMJ 1999; 318: 793-6.