(Redrawn with permission from Rymer J, Davis G, Rodin A et al. 2003 Preparation and Revision for the DRCOG, 3rd edn. Edinburgh: Churchill Livingstone, p. 382.)

Figure 14.2 Diameters of the pelvis, the pelvic outlet. The boundary of the outlet from the symphysis pubis, down the inferior rami of the pubic bones to the ischial tuberosities, and then obliquely upwards and posterior along the sacrotuberous ligaments to the tip of the fifth sacral vertebra. Anteroposterior: 13 cm; transverse: 11 cm; oblique diameter 12 cm.

(Redrawn with permission from Rymer J, Davis G, Rodin A et al. 2003 Preparation and Revision for the DRCOG, 3rd edn. Edinburgh: Churchill Livingstone, p. 383.)

The pelvic outlet is the opposite, with a transverse diameter of 11 cm and an anteroposterior diameter of 13 cm. The ischial spines can be palpated vaginally and are used as the landmarks to define the descent or station (in centimetres above or below) of the fetal presenting part.

3. The passenger is the fetus and the fetal head diameters (Fig. 14.3) are important to allow ease of descent:

a. The attitude of the fetal head in labour is the degree of flexion, and the smallest diameter of the fetal head to allow ease of passage through the pelvis is at maximum flexion when the diameter is approximately 9.5 cm. A lesser degree of flexion (deflexed) will increase the diameter of the vertex or fetal head, with increasing deflexion resulting in a brow or face presentation.

b. Position of the fetal head describes the relationship of its sagittal suture to the pelvis and is described by the position of the fetal occiput. Usually, the fetal head enters the pelvis in a left occipital transverse (LOT) position and then rotates as it passes through the pelvis by 90° clockwise to an occiput anterior (OA) position. However, failure of the fetal head to rotate results in a persistent occiput transverse (OT) position and in fewer than 5% of cases the opposite is the case, where the occiput faces posteriorly (OP); both situations that result in a difficult spontaneous delivery without assistance.

c. The size of a normally formed fetal head will rarely cause obstruction. The fetal head is highly malleable and will mould as it passes through the pelvis, resulting in palpable overlapping suture lines on vaginal assessment. Cervical pressure on the fetal scalp during labour may result in scalp swelling or oedema, which is called caput. Both caput and the degree of moulding will be an indication of possible obstruction.

Figure 14.3 The fetal skull diameters.

(Redrawn with permission from Rymer J, Davis G, Rodin A et al. 2003 Preparation and Revision for the DRCOG, 3rd edn. Edinburgh: Churchill Livingstone, p. 381.)

Mechanical features of the vertex in labour

The mechanics of labour described above cause changes in the attitude of the fetal head during descent into the pelvis (Fig. 14.4) and are summarized in stages as:

1. Descent: the fetal head often descends during the last few weeks of pregnancy in the nulliparous patient, but this descent may not occur until just before the onset of labour in multiparous patients or also in Afro-Caribbean women because of the shape of their pelvises.

2. Engagement: this occurs when the maximum diameter of the fetal head has passed through the pelvic inlet. It is usually described in fifths of the fetal head that can be palpated abdominally, with engagement being defined as less than or equal to two-fifths of the fetal head palpable above the pelvic brim.

3. Flexion: the fetal head flexes as it descends through the pelvis in order to allow its smallest diameter to traverse the pelvis. With maximum flexion the posterior fontanelle can be easily palpated vaginally.

4. Internal rotation: as the fetal head descends it rotates from a LOT position to OA, as described above (Fig. 14.5).

5. Extension: the fetal head remains flexed until it reaches the perineum and then begins to extend as the head crowns as it is about to be delivered.

6. External rotation (restitution): as the fetal head is delivered it reverts to the transverse position (OT).

7. Lateral flexion: when the head is delivering the anterior shoulder appears, followed by the posterior shoulder with the trunk delivering by lateral flexion.

Figure 14.4 Descent of fetal head vaginally described in relation to the ischial spine.

Figure 14.5 Rotation of fetal head during descent from left occipital transverse to occiput anterior.

Assessment of labour

The prompt and accurate diagnosis of labour is crucial in the management and assessment of the progress of labour.

Management

Once the diagnosis of labour has been made then the membranes can be ruptured to assess the liquor for the presence of meconium, which will provide information on fetal well-being. A partogram is a visual record of labour progress and records a variable amount of information depending on each individual obstetric unit. The following is a list of usual information recorded in a partogram (Fig. 14.6):

1. Patient details

2. The date and time of admission

3. Maternal vital signs

4. A progressive representation of cervical dilatation (descent of the head). The partogram may include an action line denoting a minimum acceptable rate of cervical dilatation (usually 1 cm/h for a primigravid patient). If progress falls below the action line, then medical intervention may be considered

5. Details on the contractions should include frequency (usually described as the number occurring in 10 minutes), duration and strength

6. The fetal heart rate by intermittent auscultation or continuous fetal monitoring

7. Colour of liquor and time of rupture of membranes

8. Drugs given, including oxytocin and analgesics

9. Maternal urine production and urinalysis for ketones and/or protein.

Figure 14.6 Typical partogram illustrating graphically essential information of labour progress. BP, blood pressure.

Progress of labour

The fundamental process of labour is progressive dilatation of the cervix and descent of the presenting part.

Primiparous and multiparous patients are very different in their labour progress. A primiparous labour is often slow, but a slow multiparous labour is always of concern.

Primiparous labour

Labour should proceed at a rate of at least 1 cm cervical dilatation per hour in a primiparous patient. The first stage should, therefore, last for 10 hours with 2 hours for the second stage. Labour that lasts for longer than 12 hours is said to be prolonged. However, the primiparous uterus is notoriously inefficient as it has not experienced labour before, so that even if the contractions feel strong and frequent they may be having little effect on cervical dilatation. This is correctable if diagnosed early by performing an amniotomy if the membranes are still intact and by commencing an oxytocin infusion to augment labour. Careful clinical monitoring is required to ensure that contractions do not exceed one every 2 minutes or hypertonia results, with fetal hypoxia caused by restriction of the maternal placental blood flow. Oxytocin is, therefore, administered by titrating the infusion against the uterine contractions to achieve efficient uterine action and each obstetric unit will have protocols for concentration and infusion rates (Fig. 14.6). If full dilatation is not foreseeable within 12 hours, then caesarean section may need to be considered as the woman will become exhausted and there will be increasing risk of fetal hypoxia. The partogram is a crucial guide to labour progression. An individual decision is taken by each woman on the recommendation of the obstetrician and midwife.

Cephalopelvic disproportion is diagnosed when a woman has been unable to deliver a fetus despite adequate uterine activity and in the absence of malposition of the fetus. This disparity between the size of the fetus and the maternal pelvis is uncommon in the UK in the absence of pelvic abnormality.

Multiparous labour

The multiparous uterus is not inefficient as it has laboured previously. However, it should be noted that a multiparous patient may not have laboured before (i.e. caesarean section) and in this case the uterus will behave in the same way as that of a primiparous woman. Therefore, slow progress is a cause for concern and is usually the result of a larger baby in this pregnancy or because of malposition. The multiparous uterus is prone to rupture and so the use of oxytocin should only be considered after careful evaluation.

Fetal surveillance in labour

The aim of fetal monitoring in labour is to detect fetal hypoxia. Each fetus will behave differently during the stresses of labour depending on its individual reserve and in particular a fetus that is compromised antenatally is more vulnerable during labour.

Methods

1. Amniotic fluid and liquor: the absence of liquor is associated with intrauterine growth retardation. Meconium is the passage of stool by the fetus in utero and is caused by vagal stimulation of the gut as a result of an episode of hypoxia. Some units will grade the meconium during labour from 1 to 3. Grade 1 meconium is lightly stained fluid (meconium that is very diluted by adequate liquor), grade 2 is moderately stained and grade 3 is a heavy, thick liquid associated with the fresh passage of meconium in the presence of reduced liquor, which is of particular concern, indicating fetal hypoxia.

2. Intermittent auscultation with either a Pinard’s stethoscope or a Sonicaid. This is sometimes the method of choice in monitoring a low-risk labour and should be performed for 1 minute after a contraction and every 15 minutes to detect accelerations or decelerations of the fetal heart rate.

3. Continuous fetal monitoring using either an abdominal transducer (as part of the CTG) or a fetal scalp electrode. This will give a continuous real-time record of the fetal heart rate response to labour. The CTG should always be interpreted as part of the whole clinical picture, including stage of labour, maternal analgesia and status of the uterine contractions.

4. Fetal blood sampling is performed when the CTG suggests fetal compromise in labour and is interpreted on the basis of the fetal blood pH. A pH of greater than 7.25 is considered normal; a pH of between 7.20 and 7.25 is a borderline result that will need to be repeated within 1 hour; and a pH of less than 7.20 is abnormal, indicating immediate delivery.

Fetal heart rate patterns

There are three features of the fetal heart rate that should be noted – the baseline, beat-to-beat variability and the presence of accelerations or decelerations (see Fig. 14.7 for examples of CTG traces):

• Normal: the normal baseline should be between 110 and 160 beats per minute (bpm). Baseline beat-to-beat variability should be 5–25 bpm. Accelerations from baseline of 10–15 bpm will indicate a healthy fetus.

• Baseline tachycardia: a baseline fetal heart rate of greater than 160 bpm can be associated with prematurity, hypoxia, maternal pyrexia or drugs and fetal distress if also in the presence of any other abnormality.

• Baseline bradycardia: a baseline fetal heart rate of less than 110 bpm may be associated with postmaturity, hypoxia or heart block. A baseline of less than 90 bpm is usually indicative of impending fetal demise.

• Baseline variability: variability is the presence of irregular accelerations from baseline, and loss of beat-to-beat variability can indicate a sleep pattern if it lasts for less than 40 minutes. If it is prolonged beyond this it indicates hypoxia. Increase in variability may also indicate acute hypoxia.

• Early decelerations: these occur with the onset of a contraction and the fetal heart rate returns to baseline by the end of the contraction. These are usually caused by fetal head compression during descent and are benign.

• Late decelerations: these occur when the fetal heart rate drops after the peak of the contraction, with slow recovery to baseline after the contraction. Late decelerations are associated with fetal hypoxia.

• Variable decelerations: these decelerations, as the name suggests, occur at variable times during labour, often with no association to the contraction, and usually indicate cord compression.

Figure 14.7 (A) Normal baseline (between 110 and 160 beats per minute (bpm)) is indicated by the fetal heart rate when stable (note: accelerations and decelerations are absent in this trace section).

(B) Bradycardia is defined as a baseline heart rate of <110 bpm.

(C) A suspicious tachycardia is defined as being between 160 and 170 bpm, whereas a pathological pattern is above 170 bpm.

(D) Reduced variability (a flat trace).

(E) Acceleration is defined as a transient increase in heart rate of greater than 10–15 bpm for at least 15 seconds.

(F) Decelerations.

(H) Decelerations.

(G) Decelerations.

Third stage of labour

The third stage of labour is the period between delivery of the fetus and delivery of the placenta. In a normal physiological third stage, the uterus continues to contract, which in combination with the reduced surface area of the uterus causes the placenta to separate from the uterine wall. During this phase there is usually a small gush of blood indicating that separation has occurred. The normal haemostatic processes that occur during this stage will be interfered with in the following situations:

• Morbid adherence of the placenta

• A prolonged labour

• When the uterus has been overdistended as a result of a multiple pregnancy

• As a result of halothane anaesthesia.

Physiological management

Inform the woman of the benefits of active management and document her choice in her notes. Physiological management is contraindicated where there has been any intervention (e.g. induction of labour), previous postpartum haemorrhage or cause for current obstetric concern (i.e. antepartum haemorrhage, postpartum haemorrhage or preterm labour).

Following delivery of baby, wait until cord pulsation has stopped, unless the baby requires resuscitation, is ill or requires observation, in which case active management should be undertaken. The baby can be handed to the mother, but kept at the same level as the uterus until the cord has been clamped and cut. When the cord pulsation has stopped, the cord is then clamped and cut and the mother should be encouraged to breastfeed. Release the clamp on the placental cord and allow cord blood to drain. Measure blood loss and observe the mother’s colour, pulse rate and respirations.

Active management

In order to reduce the risk of postpartum haemorrhage because of retained placenta many units have a policy of active management of the third stage unless the woman requests physiological management.

The active management of the third stage of labour is carried out with the use of drugs, early clamping and cutting of the umbilical cord and controlled cord traction for the delivery of the placenta. Controlled cord traction is performed using the Brandt–Andrews technique, which involves downward traction on the cord with the other hand placed suprapubically to lift the uterus upwards.

The oxytocic drug of choice is Syntometrine 1 ml (a combination of oxytocin and ergometrine), given intramuscularly as the anterior shoulder of the baby is delivered. Women who are anaemic or who have a history of postpartum haemorrhage should be given ergometrine 250 μg intravenously instead or in addition.

Contraindications to the use of Syntometrine/ergometrine include:

• Hypertension

• Cardiac conditions

• Asthma

• History of cholecystitis

• Women who have received betamimetics.

In these cases, give 10 units of oxytocin intramuscularly/intravenously and await signs of placental separation (a gush of blood, lengthening of the cord, contracted uterine fundus), which should occur within 10–15 minutes. The placenta may become visible at the vulva or the mother may feel a heavy sensation or an urge to push. If the signs of separation have occurred, but the placenta has not delivered, vaginal examination will confirm whether the placenta is in the vagina. If the placenta is undelivered by 30–60 minutes, then manual removal of the placenta under anaesthesia (epidural will suffice, if in place, otherwise a spinal or general) may need to be considered.

Once the placenta has delivered it should be carefully inspected to ensure completeness and the genital tract should be inspected for any lacerations that may need to be repaired.

Cephalic malpositions

1. OP: this is the commonest malposition and is caused by a posterior rotation of the fetal head during descent and results in deflexion of the fetal head and thus a larger head diameter traversing the pelvis so that obstruction is caused. It is associated with inefficient uterine action, pelvic shape variants and epidurals. This malposition may be corrected as labour progresses spontaneously or with an oxytocin infusion if the contractions are poor. The earlier slow progress is diagnosed as being caused by an OP presentation, the better the chance there is of rotation to OA. However, the fetus may be delivered in that position (face to pubis) spontaneously if the pelvic diameters are adequate, but an instrumental delivery may be required to rotate the fetal head to OA or to deliver face to pubis.

2. OT: again this is caused by incomplete rotation of the fetal head during labour. If this position persists in the second stage, then delivery will not occur unless rotated to OA manually or with Kielland forceps or the ventouse. Both OP and OT instrumental deliveries are increasingly being performed in theatre, with early recourse to caesarean section if required.

3. Brow presentation: this is caused by hyperextension of the fetal neck in labour and is generally incompatible with a vaginal delivery (may deliver if fetus is preterm) as the presenting diameter is too large (mento-vertex diameter is usually 13 cm), and a caesarean delivery is indicated unless flexion occurs during the course of labour.

4. Face presentation: this is the result of complete extension of the fetal neck. The facial features can be felt on vaginal examination and vaginal delivery may be possible if the chin is anterior (mento-anterior) as it will catch on the pubic bone during descent in the pelvis, causing the fetal neck to flex and, therefore, allow for further rotation. If the chin is posterior (mento-posterior), flexion is impossible and caesarean section is indicated.

Induction of labour

Labour is induced when external methods are used to start labour artificially. This is different to augmentation, which is use of external methods to enhance uterine contractions after labour has begun spontaneously. After induction of labour has commenced, the risk of operative vaginal delivery is increased 1.5-fold and that of caesarean section is increased 1.8-fold.

Indication

This is a decision made between the obstetrician, midwife and patient. There are few definite indications for induction and the decision is usually a carefully weighted one to ensure the delivery of a healthy baby from a healthy mother, weighing up the risk/benefit ratio of the fetus remaining in utero versus delivery. In all these decisions two factors must always be considered:

1. The risk to mother and fetus if the pregnancy were allowed to continue

2. The risk to the mother of complications of induction and to the fetus of prematurity.

Common reasons for induction include:

• Postmaturity: when pregnancy extends beyond the due date, as studies have demonstrated an increase in perinatal mortality with increasing postmaturity as a result of decreased placental function. The time frame for this varies between units, but is usually at 41–42 weeks (despite the definition of term being until 42 weeks)

• Intrauterine growth retardation or antepartum haemorrhage

• Maternal hypertension

• Diabetes

• Poor obstetric history

• Maternal request.

Contraindications are defined as the following:

• Absolute: acute fetal compromise, unstable lie (if the lie stabilizes to cephalic, then controlled artificial rupture of the membranes (ARM) may be performed), placenta praevia and pelvic obstruction.

• Relative: previous caesarean section (although there are differing opinions in this situation), breech presentation and prematurity.

Method

The method of induction will usually depend on the cervical assessment, which will normally be undertaken at the time of the decision to induce (Table 14.1):

• Medical: insertion of prostaglandin gel or pessaries into the posterior vaginal fornix. Particular care should be exercised when using prostaglandins in a multiparous woman or a woman with a uterine scar, because of the risk of overstimulation. All prostaglandin administrations should be followed by a CTG for a minimum recording of 1 hour. Usually, following the second dose of prostaglandin, labour will start spontaneously. Alternatively, the cervix will have ripened sufficiently to allow surgical induction to proceed.

• Surgical induction of labour (ARM): if the cervix is favourable (Bishop’s score of >7) (Table 14.1), or the hindwaters are ruptured, there is no advantage in further use of prostaglandin. A vaginal examination should reveal the presence of fetal membranes in advance of the fetal head, and ARM can be performed using an amnihook.

• Following ARM multiparae may go into labour spontaneously as prostaglandins are released as the membranes rupture. To reduce unnecessary venous cannulation they may be left to mobilize for 2–4 hours to allow spontaneous contractions to begin. This will rarely be effective in primiparae and, therefore, an oxytocin infusion should be commenced immediately. The oxytocin regime for induction of labour is the same as that used for augmentation.

Table 14.1 Bishop’s score used to assess suitability for induction

Complications

• Uterine hypertonia with possible rupture

• Fetal distress

• Precipitate delivery

• Operative delivery

• Iatrogenic prematurity

• Amniotic fluid embolus

• Systemic effects of prostaglandins, including vomiting and diarrhoea.

Operative delivery

Instrumental delivery allows the use of traction, usually combined with maternal effort, to expedite delivery of the fetus in the second stage of labour. The shape of the maternal pelvis will only allow the fetal head to deliver if it is in the OA or, occasionally, if the pelvis is adequate, the OP position. Therefore, rotation to these positions may be required either manually or with the use of a ventouse or rotational forceps.

Indications

• Fetal distress in the second stage

• Delivery of the aftercoming head in a breech delivery

• Prolonged second stage (usually after 1 hour of active pushing) or maternal distress

• Maternal disease where active pushing would be harmful, e.g. cardiac disease

• Dural tap.

Criteria for operative vaginal delivery

If an operative vaginal delivery is deemed appropriate, the operator must be confident that delivery will be easily achieved. If there is any doubt, then the procedure should be performed in the operating theatre (trial of instrumental delivery) with a full team present (obstetrician, midwife, anaesthetist and paediatrician) and ready to proceed immediately to caesarean section.

The following criteria must be met before proceeding to operative vaginal delivery, as both forceps and ventouse are potentially dangerous instruments:

• Patient understands and accepts the need for intervention.

• There is a valid indication for expediting delivery.

• Fetus must be in a cephalic presentation and the head not palpable above the pelvic brim (the exception being the use of forceps to aid delivery of the aftercoming head in vaginal breech delivery). On vaginal examination the head must be at or below the level of the ischial spines.

• Cervix must be fully dilated and the membranes ruptured.

• Maternal bladder should be empty.

• There should be no excessive moulding or caput, and the operator must be certain of the position of the fetal head.

• There must be adequate analgesia.

Caesarean section

Caesarean section rates are continuing to rise throughout the world and this is a cause for concern for many, including the World Health Organization. In the developed world, rates of 15–25% are common. The procedure is described later, but is usually performed through a Pfannenstiel incision and an incision through the lower uterine segment. A classical caesarean section is one performed through a vertical upper uterine segment incision.

Complications

• Haemorrhage

• Infection: although this is less of a problem when prophylactic antibiotics are used

• Thrombosis: less common if anticoagulants are used appropriately in at-risk patients

• Ileus.

Labour following caesarean section

The indication for repeat caesarean section depends on the reason for the first caesarean section and a clear history of that labour is essential in this decision-making. There is little clear evidence on the appropriate choice of delivery for women who have had one previous caesarean section, although most would advise a woman with two previous sections to have caesareans for any future pregnancy. Some obstetricians would advocate the adage ‘once a caesarean, always a caesarean’; however, approximately 70% of women with one previous caesarean will achieve a vaginal delivery. Rupture of the uterine scar can occur in up to 0.5% of these women and so a ‘trial of labour’ must be carefully managed.

Management

• Caution regarding induction of labour. If the cervix is favourable, an ARM may be performed with cautious use of oxytocin, but few would consider administering prostaglandins to ripen the cervix.

• Continuous fetal monitoring should be carried out.

• Epidurals are appropriate.

• Avoid prolonged labours: failure to progress should alert the obstetrician to consider caesarean section. Women with a previous caesarean section who present in spontaneous labour should not have augmentation for slow progress.

Complications

The major complication of ‘trial of labour’ (or ‘trial of scar’) is that of scar rupture. This is an obstetric emergency and can be recognized by:

• Evidence of fetal distress

• Scar pain and tenderness

• Vaginal bleeding (and occasionally haematuria)

• Diminished contractions

• Maternal collapse.

In this situation or if there is even suspicion of scar rupture, the woman must be resuscitated (see Chapter 17, unconscious patient) and immediate arrangements made for laparotomy and caesarean section.

Prelabour rupture of membranes

At term, this occurs in 10% of women and the cause is often unknown. A clear history can be taken from the woman, who characteristically will describe a ‘gush’ of fluid followed by a continuous trickle. The diagnosis is crucial as many women at term may experience urinary incontinence. Diagnosis can only be made by direct visualization of amniotic fluid draining through the cervix by speculum examination. Ultrasound and the use of nitrazine sticks are of limited benefit.

If rupture of the membranes is suspected, digital examination should be avoided and the diagnosis made using a sterile speculum. A vaginal swab is taken and maternal observations recorded to ensure there is no evidence of infection. Similarly, the fetal heart rate is monitored to assess fetal well-being. The majority of women (80%) will labour within 24–48 hours, and if this is not the case then augmentation of labour is recommended. If there is any evidence of compromise – maternal infection, fetal distress on CTG or meconium – then labour should be augmented immediately.

Preterm prelabour rupture of membranes (PPROM) is defined as rupture of the membranes before labour at less than 37 weeks’ gestation. The cause is often unknown, but it occurs in approximately 40% of all preterm labours. The clinical features are similar to the above and similarly the diagnosis is vital, but the management is very different. In PPROM the risks of maternal and fetal infection must be balanced against the risks of prematurity. At gestations of greater than 34 weeks there is little to be gained by waiting and the labour should be induced. However, at gestations before this the management is conservative and the patient is usually admitted for regular monitoring of both herself and the fetus, and steroids administered. The use of prophylactic antibiotics is now accepted in improving perinatal outcome. Management should involve the following:

• Admit patient for observation

• Four-hourly maternal temperature and pulse

• Daily CTG

• Twice-weekly blood tests for white cell count and C-reactive protein

• Weekly or 2-weekly fetal ultrasound assessment

• Can consider allowing patient home to self-monitor with instruction to return if there are any concerns.

Signs of impending infection or chorioamnionitis include:

• Maternal pyrexia

• Maternal leukocytosis or raised C-reactive protein

• Uterine tenderness

• Fetal tachycardia

• Meconium or foul-smelling liquor.

Preterm labour

This is defined as the delivery of a fetus between 24 and 37 completed weeks of pregnancy.

Low-birth-weight infants are those weighing less than 2500 grams and very-low-birth-weight infants are those weighing less than 1500 grams at delivery.

Incidence

Preterm labour occurs in 5–10% of cases, but a further 5% of labours are complicated by ‘threatened’ preterm labours that continue on to deliver at term. Although preterm labour accounts for the main cause of perinatal mortality and morbidity, survival rates are improving as neonatal intensive care advances. However, long-term morbidities, like cerebral palsy, blindness and lung disease, are common in this group of infants.

Aetiology

The pathophysiological processes involved in preterm labour are still unknown, although much research is ongoing and various factors, described below, have been shown to have an association.

Maternal

• Infection (e.g. urinary tract)

• Chorioamnionitis

• Antepartum haemorrhage

• Pre-eclampsia

• Polyhydramnios

• Uterine abnormalities like cervical incompetence.

Fetal

• Intrauterine growth retardation

• Congenital abnormality

• Intrauterine death

• Multiple pregnancy.

Other risk factors include maternal age <20 years, maternal smoking and low socioeconomic group. However, the greatest risk factor for preterm labour is a previous preterm labour.

Maternal genital tract infection has been linked to preterm labour, in particular with the organisms Trichomonas vaginalis and Chlamydia trachomatis, or infection with bacterial vaginosis. Recent trials have shown benefit in the use of prophylactic antibiotics in women with bacterial vaginosis demonstrated on a high vaginal swab.

Assessment

A correct diagnosis of labour is just as important in preterm patients:

• History and examination will include precipitating factors and cervical assessment.

• Ensure accurate dating information regarding gestation.

• CTG to assess fetal well-being and uterine activity.

• Ultrasound assessment to confirm fetal well-being, exclude fetal abnormality, estimate fetal weight and confirm presentation.

Management

1. Steroids to promote fetal lung maturity: glucocorticoids administered by injection to the mother 24 hours before delivery have been shown to reduce perinatal mortality and morbidity by promoting lung maturity in babies born between 24 and 34 weeks. There is at present no evidence to suggest that repeated doses are of any benefit.

2. Tocolysis: tocolytics act by inhibiting uterine smooth-muscle contractility. The most common agents used are the beta-sympathomimetics like ritodrine and salbutamol given as an infusion intravenously. This delays rather than stops preterm labour, to allow administered steroids to have an effect or if the mother needs to be transferred due to inadequate neonatal facilities being available. Tocolysis is contraindicated in cases with ruptured membranes or following an antepartum haemorrhage and should be used with caution with careful maternal monitoring as these infusions have significant side effects, including tremor, anxiety, tachycardia and pulmonary oedema.

3. Delivery: adequate neonatal care facilities must be available to ensure optimum outcome, otherwise an in-utero transfer should be arranged. Vaginal delivery is usually recommended for preterm delivery, especially if there is a cephalic presentation. Mode of delivery of a breech presentation is controversial, but again can be safely carried out vaginally in the care of an experienced obstetrician. Instrumental delivery is conducted for the usual reasons, but the ventouse is contraindicated in fetuses of less than 34 weeks’ gestation, because of possible risk of injury to the immature fetal head and intracranial haemorrhage.

Pain relief in labour

Labour is painful, although each woman’s response to labour is different, as is each individual woman’s experience with her own previous labours.

A woman’s expectation of pain can be greatly diminished by carefully addressing her fears and giving precise, accurate and relevant information on the options for pain relief in labour.

Causes of labour pain

• Stretching of the cervix during dilatation

• Ischaemia of the uterine muscular wall during labour

• Stretching of the vagina and perineum during the second stage.

Self-help and natural sources (non-pharmacological methods)

Increasing numbers of women use non-pharmacological methods to maintain control of their labour. An important feature of any labour is the removal of anxiety and the support of a trusted companion and this can be emphasized in the antenatal class:

• Relaxation: being aware of physical tension and being able to relax consciously both during and between contractions helps to reduce pain.

• Changing position and moving: many women find pelvic rocking and other rhythmic movements help with pain.

• Massage can be a great aid to localized pain in the lower back, hips and thighs.

• Music: this can be both relaxing and a distraction from the pain of contractions.

• Warm baths or showers: many women find warm water very soothing, especially in early labour, and some professionals may advocate the options of a water birth in low-risk pregnancies.

• Natural therapies include acupuncture, aromatherapy, herbal remedies, homeopathy and hypnotherapy and many women find these helpful during labour. A properly qualified practitioner must be consulted.

• Transcutaneous electrical nerve stimulation (TENS) consists of a machine which sends small electrical impulses between four electrodes taped to the woman’s back. The woman controls the strength of the impulses by turning a small dial. It reduces pain by interfering with the pain messages to the brain and also by increasing the production of the woman’s endorphins (natural painkillers). Women are advised to start using TENS in early labour as the pain-relieving effect is built up over time.

Pharmacological methods of pain relief

Entonox is a premixed 50% oxygen/50% nitrous oxide gas that is self-administered and is available in all delivery suites. Entonox has a short half-life, but is safe for both mother and fetus. It is important to educate the woman beforehand as to the correct use of Entonox. Ideally, she should take deep inspirations of the gas at the onset of the contraction and not at the peak of the contraction pain to allow adequate analgesia.

Pethidine is usually administered as an intramuscular injection of between 50 and 150 mg. It generally works within 20 minutes, but many women become nauseous so it is often given in conjunction with an antiemetic like metoclopramide 10 mg. It may be administered 4–6-hourly, but it is rare that more than two doses are required. It does cross the placenta, causing reduced variability in the fetal heart rate, and, if given within 4 hours of delivery will cause significant respiratory depression in the neonate. If this occurs, then the narcotic antagonist naloxone should be given to the neonate.

Epidural analgesia provides the most effective form of pain relief in labour and is becoming a more popular choice with most women. The epidural space is the potential space lying outside the dura mater. Injection of local anaesthetic into this space will produce analgesia in the spinal nerve roots (Fig. 14.12). The nerve roots T10–L1 need to be targeted to give adequate analgesia during the first stage of labour and the sacral nerve roots for the second stage. A more extensive block to T8 will be required for caesarean sections. To administer an epidural, an indwelling plastic catheter is introduced into the epidural space (usually at L2–3 or L3–4) through a needle with a curved tip (Tuohy needle). The local anaesthetic usually administered is bupivacaine, but this causes motor blockade so that more often it is given in combination with the opioid fentanyl, to good effect. This mixture is becoming more popular as it can allow the woman limited mobility with effective analgesia. After an initial test dose, the analgesia can be topped up periodically as required or an infusion pump can be commenced. Contraindications to epidurals include:

• Coagulopathy: this may cause haemorrhage into the epidural space. This may be a particular problem in pre-eclampsia

• Recent antepartum haemorrhage: epidural analgesia may be associated with a profound hypotensive episode, especially in the presence of haemorrhage

• Sepsis at the potential site for epidural

• Spinal abnormalities

• Active neurological disease

• Allergy to local anaesthetic.