Management of labour

Stages of labour

The early preparation (pre-labour phase) goes on for days and weeks, while the onset of painful uterine contractions and delivery is shorter and the process is called parturition or labour . The cervix ripens by becoming softer, shorter and dilated, which takes a greater speed with onset of uterine contractions.

For purposes of clinical management, the ‘observed’ labour, which is a continuum, is divided into three stages:

• The first stage commences with the onset of regular painful contractions and cervical changes until it reaches full dilatation and the cervix is no longer palpable. The first stage is divided into an early slow latent phase when the cervix becomes effaced and shortens from 3cm in length and dilates up to 5 cm. Following recent studies, the latent phase has been defined to continue to 5 cm, and an active phase when the cervix dilates from 5cm to full dilatation or 10cm. The evidence comes from recent studies that have described rates of cervical dilatation in a large number of nulliparous and multiparous women admitted in spontaneous labour. Median time in nullipara for cervical change of 3–4 cm was 1.8 hours, 4–5 cm was 1.3 hours, 5–6 cm was 0.8 hours, 6–7 cm was 0.6 hours, 7–8 cm was 0.5 hours, 8–9 cm was 0.5 hours and 9–10 cm was 0.5 hours. Based on this, one could state that the active phase starts from 5 cm cervical dilatation.

• The second stage is the duration from full cervical dilatation to delivery of the fetus. This is subdivided into a pelvic or passive phase, when the head descends in the pelvis, and an active or perineal phase, when the mother gets a stronger urge to push and the fetus is delivered with the force of the uterine contractions and the maternal bearing-down effort.

• The third stage is the duration from the delivery of the newborn to delivery of the placenta and membranes.

Onset of labour

It is often difficult to be certain of the exact time of onset of labour because contractions may be irregular and may start and stop with no cervical change, i.e. ‘false labour’. The duration of labour for management purposes is based on the observed progress of the contractions and cervical changes along with the descent of the head. This concept may have to be judged based on the place of practice, as in some remote areas a mother may be brought in after a day of labour with no progress. Her general condition and findings of the maternal and fetal conditions should dictate management. In the rare cases of cervical stenosis that can occur after surgery to the cervix, normal contractions of labour may produce thinning of the cervix without cervical dilatation.

The clinical signs of the onset of labour are:

• Regular, painful uterine contractions that increase in frequency, duration and intensity that produce progressive cervical effacement and dilatation and descent of the fetal presenting part.

• The passage of blood-stained mucus from the cervix, called the show , is associated with but is not on its own an indicator of the onset of labour.

• Similarly, rupture of the fetal membranes can be at the onset of labour, but this is variable and may occur without uterine contractions. If the latent period between rupture of membranes (ROM) to onset of painful uterine contractions is greater than 4 hours, it is called pre-labour rupture of membranes (PROM), and this can occur at term or in the pre-term period, when it is called pre-term pre-labour rupture of membranes (PPROM).

Uterine activity in labour: the powers

The uterus exhibits infrequent, low-intensity contractions throughout pregnancy. As full term approaches, uterine activity increases in frequency, duration and strength of contractions. By palpation or external tocography one can identify the frequency and duration of contractions, but intrauterine pressure catheters are needed to assess the strength of contractions. It is likely that labour would be established if two contractions each lasting for >20 seconds are observed in 10 minutes in a regular manner. Normal resting tonus in labour starts at around 10–20mmHg and increases slightly during labour ( Fig. 11.1 ). Contractions increase in intensity with progress of labour, which in some ways is characterized by the increasing duration of contractions. The World Health Organization (WHO) recommends contraction recording on the partograph based on the frequency and duration of contractions.

Progressive uterine contractions cause effacement and dilatation of the cervix as the result of shortening of myometrial fibres in the upper uterine segment and stretching and thinning of the lower uterine segment ( Fig. 11.2 ). This process is known as retraction . The lower segment becomes elongated and thinned as labour progresses, and the junction between the upper and lower segment rises in the abdomen. Where labour becomes obstructed, the junction of the upper and lower segments may become visible at the level of the umbilicus; this is known as a retraction ring (also known as Bandl’s ring ).

A pacemaker for the uterus has never been demonstrated by anatomical, pharmacological, electrical or physiological studies. The electrical contraction impulse starts in one or the other uterine fundal region and spreads downwards through the myometrium. Contractions are stronger and last longer in the fundus and upper segment than in the lower segment. This fundal dominance is essential for progressive effacement and dilatation of the cervix. As the uterus and the round ligaments contract, the axis of the uterus straightens and pulls the longitudinal axis of the fetus towards the anterior abdominal wall in line with the inlet of the true pelvis.

The realignment of the uterine axis promotes descent of the presenting part as the fetus is pushed directly downwards into the pelvic cavity ( Fig. 11.3 ).

The passages

The shape and structure of the bony pelvis have already been described (see Chapter 1 ). The size and shape of the pelvis vary from woman to woman. Not all women have a gynaecoid pelvis; some may have a platypelloid, anthropoid or android pelvis, thus influencing the outcome of labour. Softening of the sacroiliac ligaments and the pubic symphysis allows expansion of the pelvic cavity, and this feature, along with the dynamic changes of the head diameter brought about by flexion, rotation and moulding, facilitates normal progress and spontaneous vaginal delivery.

The soft tissues of the pelvis are more distensible than in the non-pregnant state. Substantial distension of the pelvic floor and vaginal orifice occurs during the descent and birth of the head. The distensible nature of the pelvic soft tissues, vagina and perineum helps to reduce the risk of tearing of the perineum and vaginal walls during descent and birth of the head.

The mechanism of labour

The pelvic inlet offers a larger lateral than an anteroposterior diameter. This promotes the head to normally engage in the pelvis in the transverse position. The passage of the head and trunk through the pelvis follows a well-defined pattern because the upper pelvic strait is transverse, the middle pelvic strait is circular and the outer pelvic strait is anteroposterior. The fetal head presents by the vertex in 95% of the cases, and hence is called normal presentation . With the vertex presentation, the head is well flexed in 90% of the cases and the head rotates to an occipitoanterior position and presents the shortest diameters, i.e. anteroposterior suboccipitobregmatic (9.5cm) and lateral biparietal (9.5cm) diameters; hence, the occipitoanterior position where the occiput is in the anterior half of the pelvis is called the normal position . A deflexed or extended head presents as an occipitoposterior or transverse position and with further extension as a brow or face presentation. Labour with an occipitoposterior position is prolonged as a larger anteroposterior diameter of occipitobregmatic or occipitofrontal diameter (11.5cm) presents to the pelvis. With the brow presentation, entry of the head into the pelvic brim is difficult, as it presents the largest anteroposterior mentovertical diameter (13.5cm). The brow presentation can flex to a vertex or extend to a face presentation. If there is no progress of cervical dilatation, the baby is best delivered by caesarean section in a term brow presentation.

The process of normal labour therefore involves the adaptation of the fetal head to the various segments and diameters of the maternal pelvis, and the following processes occur ( Fig. 11.4 ):

• 1.

  Descent occurs throughout labour and is both a feature and a prerequisite for the birth of the baby. Engagement of the head normally occurs before the onset of labour in most primigravid women but may not occur until labour is well established in a multipara. Descent of the head provides a measure of the progress of labour.

• 2.

  Flexion of the head occurs as it descends and meets the medially and forward-sloping pelvic floor, bringing the chin into contact with the fetal thorax. Flexion produces a smaller diameter of presentation, changing from the occipitofrontal diameter, when the head is deflexed, to the suboccipitobregmatic diameter, when the head is fully flexed.

• 3.

  Internal rotation: The head rotates as it reaches the pelvic floor, and the occiput normally rotates anteriorly from the lateral position towards the pubic symphysis. This is due to the force of contractions being transmitted via the fetal spine to the head at the point the spine meets the skull, which is more posterior and due to the medially and forward-sloping pelvic floor. Occasionally, it rotates posteriorly towards the hollow of the sacrum, and the head may then deliver as a face-to-pubis delivery.

• 4.

  Extension: The acutely flexed head descends to distend the pelvic floor and the vulva, and the base of the occiput meets the inferior rami of the pubis. The head now extends until it is delivered. Maximal distension of the perineum and introitus occurs just prior to the final expulsion of the head, a process that is known as crowning when the head is seen at the introitus but does not recede in between contractions.

• 5.

  Restitution: Following delivery of the head, it rotates back to be in line with its normal relationship to the fetal shoulders. The direction of the occiput following restitution points to the position of the vertex before the delivery.

• 6.

  External rotation: When the shoulders reach the pelvic floor, they rotate into the anteroposterior diameter of the pelvis. This is accompanied by rotation of the fetal head so that the face looks laterally at the maternal thigh.

• 7.

  Delivery of the shoulders: Final expulsion of the trunk occurs following delivery of the shoulders. The anterior shoulder is delivered first by traction posteriorly on the fetal head so that the shoulder emerges under the pubic arch. The posterior shoulder is delivered by lifting the head anteriorly over the perineum, and this is followed by rapid delivery of the remainder of the trunk and the lower limbs.

The occiput normally rotates anteriorly, but if it rotates posteriorly, it deflexes and presents a larger diameter to the pelvic cavity. As a result, the second stage may be prolonged and the damage to the perineum and vagina is increased.

The third stage of labour

The third stage of labour starts with the completed expulsion of the baby and ends with the delivery of the placenta and membranes ( Fig. 11.5 ).

Once the baby is delivered, the uterine muscle contracts, shearing off the placenta and pushing it into the lower segment and the vault of the vagina.

The classic signs of placental separation include trickling of bright blood, lengthening of the umbilical cord and elevation of the uterine fundus within the abdominal cavity. The uterine fundus becomes firm to hard and smaller and rounded instead of being broad and globular and sits on top of the placenta as it descends into the lower segment.

The duration of placental separation may be compressed using oxytocic drugs administered at the delivery of the anterior shoulder.

As the placenta is expelled, it is accompanied by the fetal membranes, although the membranes often become torn and may require additional traction by using a sponge forceps to grasp them. Uterine exploration is rarely needed to complete their removal. The completeness of the placenta and membranes should be recorded after checking the cord, placenta and membranes from the amniotic as well as the chorionic sides.

The whole process lasts between 5 and 10 minutes. If the placenta is not expelled within 30 minutes, a diagnosis of retained placenta is made and the third stage considered abnormal.

Most complications of labour and delivery such as postpartum haemorrhage, pelvic or perineal haematoma and any deterioration of the maternal or newborn condition take place within the first few hours of delivery and hence in most settings the mother and baby are closely examined with periodic observations in the delivery unit for up to 2 hours before the mother and baby are sent to the postnatal ward. The observations are continued for 6 hours if the mother is to be discharged home from the delivery unit.

Pain in labour

Contractions in labour are invariably associated with pain, particularly as they increase in strength, frequency and duration with progress of labour. The cause of pain is uncertain, but it may be due to compression of nerve fibres in the cervical zone or to hypoxia of compressed muscle cells. Pain is felt in the lower abdomen and as lumbar backache when the intrauterine pressure exceeds 25mmHg.

The management of normal labour

The primary aim of intrapartum care is to deliver a healthy baby to a healthy mother. The preparation of the mother for the process of parturition begins well before the onset of labour. It is important for the mother and her partner to understand what happens during the various stages of labour. Strategies to deal with pain in labour, including mental preparation with controlled respiration, should be introduced during antenatal classes, as well as educating the mother about the regulation of expulsive efforts during the second stage of labour.

Antenatal classes should also include instructions about neonatal care and breast-feeding, although this is a process that requires reinforcement in the postdelivery period.

The mother should be advised to come into hospital, or to call the midwife in the event of a home birth, when contractions are at regular 10- to 15-minute intervals, when there is a show or when the membranes rupture. If the mother is in early labour, she should be encouraged to take a shower and to empty her bowels and bladder. Shaving of the pubic hair or abdomen is no longer considered necessary and is likely to cause abrasions with some bleeding that may become the nidus for bacterial proliferation and subsequent infection.

The home birth rate in the UK is about 2–3%, but it is common practice to organize ‘domino’ ( dom iciliary in and o ut) deliveries, whereby the mother is discharged home 6 hours after delivery, provided that the delivery is uncomplicated.

General principles of the management of the first stage of labour

The guiding principles of management are:

• Observation of the progress of labour and intervention if it is slow

• Monitoring the fetal and maternal condition

• Pain relief during labour and emotional support for the mother

• Adequate hydration and nutrition throughout labour

Observation: the use of the partogram

The introduction of graphic records of progress of cervical dilatation and descent of the head was a major advance in the management of labour. It enables the early recognition of a labour that is non-progressive. The partogram ( Fig. 11.6 ) is a single sheet of paper on which there is a graphic representation of progress in labour. On the same sheet, other observations related to labour can be recorded. There are sections to enter the frequency and duration of contractions, fetal heart rate (FHR), colour of liquor, caput and moulding, station or descent of the head, maternal heart rate, BP and temperature. The partogram should be started as soon as the mother is admitted to the delivery suite, and this is recorded as zero time, regardless of the time at which contractions started. However, the point of entry on the partogram depends on a vaginal assessment at the time of admission to the delivery suite. The value of this type of record system is that it draws attention visually to any aberration from normal progress in labour.

The use of partograms at an applied level was first introduced in remote obstetric units in Africa, where recognition that progress in labour is becoming abnormal enables early transfer to specialist units before serious obstruction occurs.

This has led to a major reduction in maternal mortality due to avoidance of uterine rupture, sepsis and postpartum haemorrhage and reduction in severe morbidity of vesico or recto vaginal fistula. Earlier recognition of obstructed labours and immediate attention by caesarean delivery where indicated prevents such tragedies.

Fetal condition

The FHR is auscultated every 15 minutes for a duration of 1 minute soon after a contraction in the first stage of labour and after every 5 minutes or after every other contraction for a duration of 1 minute in the second stage of labour. Counting for 15 seconds and multiplying by 4 or counting for 30 seconds and multiplying by 2 lead to error in the FHR observation. The FHR is charted as beats/min in the designated space in the partogram, and decelerations of heart rate that are heard soon after contractions are recorded by an arrow down to the lowest heart rate recorded on the partogram. These records are an adjunct to the actual recording of auscultated FHR in the notes and/or electronic fetal monitoring (EFM) by continuous cardiotocography (CTG).

The time of ROM, the nature of the amniotic fluid, i.e. whether it is clear or meconium stained, and quantity are also recorded. Moulding of the fetal head and the presence of caput are also noted, as they provide an indicator of cephalopelvic disproportion. The suture lines meeting is moulding +, over-riding but reducible with gentle pressure is ++ and overriding and not reducible with gentle pressure is +++. The soft tissue swelling of the scalp called caput is also marked from + to +++ but is based on the relative impression formed by the clinician.

Progress in labour

Progress in labour is measured by assessing the rate of cervical dilatation and descent of the presenting part. The progress is assessed by vaginal examination on admission and every 3 to 4 hours afterwards during the first stage of labour. Cervical dilatation is plotted in centimetres along the scale of 0–10 of the cervicograph. The cervix is expected to efface and dilate from 0 to 5cm (latent phase) in 6–8 hours in a multipara and 8–10 hours in a nullipara, followed by approximately 1 cm per hour from 5 to 10cm dilatation (active phase) in nulli and multipara, although multipara tend to dilate faster. The expected progress recorded on the chart at a rate of 1 cm per hour from admission dilatation in the active phase of labour is called the alert line, which helps to identify those who are progressing slowly. A line 2 hours parallel with the alert line called the action line can be drawn to decide on when to actively intervene with artificial ROM or oxytocin infusion to augment labour in the absence of malpresentation, disproportion or concern for fetal condition.

If the progress of cervical dilatation lags more than 2 hours behind the expected rate of dilatation, it will cut the action line, indicating the poor progress in the active phase of labour. The UK National Institute for Health and Clinical Excellence guidelines suggest that when encountered with slow progress of <1cm in 3 hours with no other changes such as cervical effacement or descent of the head in the presence of ruptured membranes, cephalopelvic disproportion should be excluded and labour augmented first by artificial ROM, and if there is no or slow progress, with an oxytocin infusion. Descent of the station of the head is charted on the partogram based on the palpable portion of the head above the pelvic brim in fifths, i.e. whether it needs 5, 4, 3, 2 or 1 finger to cover the head.

The station of the head is plotted on the 0–5 gradation of the partogram.

Descent is also recorded by assessing the level of the presenting part in centimetres above or below the level of the ischial spines and marked as −1, −2 and −3 when it is above the spines and +1, +2 and +3 if it is below the spines.

The nature and frequency of the uterine contractions are recorded on the chart by shading in the number of contractions per 10 minutes. Dotted squares indicate contractions of less than 20 seconds’ duration, cross-hatched squares are contractions between 20 and 40 seconds’ duration, while contractions lasting longer than 40 seconds are shown by complete shading of the squares. Frequency and duration of contractions can be measured by clinical palpation or external tocography. The intensity of contractions cannot be assessed by the degree of pain felt by the mother or by palpating the uterus abdominally and can only be determined by intrauterine pressure catheters. However, intrauterine catheters are not used routinely in the management of labour because their use has been shown not to improve the outcome.

Fluid and nutrition during labour

In most maternity units in the developed world, caesarean section rates now exceed 20%. The issue of what can be taken by mouth therefore becomes particularly important. If there is a likelihood that the mother will need operative delivery under general anaesthesia, then it is clearly important to avoid oral intake at any significant level during the first stage of labour. Delayed gastric emptying may result in vomiting and inhalation of vomitus if general anaesthesia for operative delivery is needed. On the other hand, most operative deliveries are now achieved under regional anaesthesia, and therefore there is a case for giving some fluids and light nutrition orally if labour is progressing normally and a vaginal delivery can be anticipated. Recent clinical trials have suggested little concern with feeding the mother with soft, easily digestible, solid nutrition in addition to fluids. Intravenous (IV) fluid replacement should be considered after 6 hours in labour if delivery is not imminent. The major cause of acidosis and ketosis is dehydration, and urine should be checked for ketones in addition to sugar and protein whenever the mother passes urine. Administration of normal saline or Hartmann’s solution is preferred, and the fluid input and output should be monitored so not to over- or under-hydrate the mother.

The classic signs of dehydration in labour include tachycardia, mild pyrexia and loss of tissue turgor. Remember that labour can be hard physical work and that the environmental temperature of delivery rooms is often raised to meet the needs of the baby rather than the mother, leading to considerable insensible fluid loss.

Pain relief in labour

A number of strategies are used in labour for the relief of pain, and these should be discussed with the pregnant mother in the antenatal period. Essentially, these techniques are aimed at reducing the level of pain experienced in labour whilst invoking minimal risk for the mother and baby.

The level of pain experienced in labour varies widely – some experience very little, whilst others suffer from abdominal and back pain of increasing intensity throughout their labour. Thus, any programme for pain relief must be tailored to the needs of the individual. The caregiver may be able to advise the best mode of pain relief based on whether the mother is nulliparous or multiparous, the current cervical dilatation, the rate of progress of labour and the extent to which the mother is feeling the pain. The mode of pain relief is best decided by the mother based on the advice given. Often this may result in a combination of methods, starting from the least to most effective method to alleviate her pain. The only technique that can provide complete pain relief is epidural analgesia.

Regional analgesia

Epidural analgesia is the most effective and widely used form of regional analgesia. It provides complete relief of pain in 95% of labouring women.

The procedure may be instituted at any time and does not interfere with uterine contractility. It may reduce the desire to bear down in the second stage of labour due to lack of pressure sensation at the perineum and reduced uterine activity due to loss of ‘Ferguson’s reflex’, which is an increased uterine activity due to reflex release of oxytocin due to the presenting part stretching the cervix and upper vagina.

A fine catheter is introduced into the lumbar epidural space, and a local anaesthetic agent such as bupivacaine is injected ( Fig. 11.7 ). The addition of an opioid to the local anaesthetic greatly reduces the dose requirement of bupivacaine, thus sparing the motor fibres to the lower limbs and reducing the classic complications of hypotension and abnormal FHR.

The procedure involves:

• Insertion of an IV cannula and preloading with no more than 500mL of saline or Hartmann’s solution.

• Insertion of the epidural cannula at the L3–L4 interspace and injection of the local anaesthetic agent at the minimum dose required for effective pain relief.

• Monitoring BP, pulse rate and FHR and adjusting maternal posture to achieve the desired analgesic effect.

The complications of epidural analgesia include:

• Hypotension: this can be avoided by preloading and the use of low-dose anaesthetic agents and opioid solutions.

• Accidental dural puncture: occurs in fewer than 1% of epidurals.

• Postdural headache: about 70% of mothers will develop a headache if a 16- or 18-gauge needle is used. A postdural headache that persists for more than 24 hours should be treated with an epidural blood patch.

Contraindications to regional anaesthesia include:

• maternal refusal

• coagulopathy

• local or systemic infection

• uncorrected hypovolaemia

• inadequate or inexperienced staff or facilities

Many women set out in labour without requesting any form of pain relief. However, as labour progresses, the realization that labour can be painful will change the requirements of the mother. It is therefore essential to have an epidural service that can be readily available so that the labour is not too far advanced before the epidural can become established.

Other forms of regional anaesthesia

Spinal anaesthesia is commonly used for operative delivery, particularly as a single-shot procedure. It is not used for control of pain in labour because of the superior safety of epidural analgesia and the ability to top up with suitable doses or as continuous infusion to get pain relief over a long period. Often a ‘spinal–epidural’ combination is used for caesarean section, with the spinal providing quick and effective anaesthesia whilst the epidural can be continued over the next 24 hours for good pain relief.

Paracervical blockade involves the infiltration of local anaesthetic agents into the paracervical tissues. This is rarely used for obstetric procedures and has the greater chance of side effects to the fetus should it enter a vessel.

Pudendal nerve blockade involves infiltration around the pudendal nerve as it leaves the pudendal canal and the inferior haemorrhoidal nerve ( Fig. 11.8 ). It was a widely used form of local anaesthesia for operative vaginal deliveries in the past but is now less frequently used, as it has been replaced by epidural anaesthesia.

Infiltration directly into the perineal tissues over the episiotomy site is still widely used for the repair of perineal wounds. Great care must be taken to avoid direct IV injection of the drug at the time of local infiltration. Toxic symptoms such as cardiac arrhythmias and convulsions may result from accidental injection of the anaesthetic drug, especially with larger dosages.

Posture in labour

Some women prefer to remain ambulant or to sit in a chair during the first stage of labour. However, most women prefer to lie down as labour advances into the second stage, although some will prefer to squat to use the forces of gravity to help expel the baby. In the past, women who had epidural anaesthesia had to remain supine because of temporary motor impairment. This has been overcome using low-dose anaesthesia combined with opiates. With such mixed epidurals, women can move about and often ambulate.

Fetal monitoring

Changes in the FHR or the passage of new meconium-stained liquor (fetal bowel motion) may suggest possibility of fetal hypoxia. These signs can occur in normal labour but more so in high-risk pregnancies and need to be studied to determine the fetal condition, if necessary, with the adjunct use of fetal scalp blood sampling (FBS). Diminution of fetal movements (FMs) on admission may indicate fetal jeopardy, and cessation of movements may indicate death and hence enquiry about FM should be made on admission in labour.

Intermittent auscultation

The FHR is monitored every 15 minutes for a period of 1 minute soon after a contraction using a handheld Doppler ultrasound transducer or Pinard fetal stethoscope in the first stage of labour. In the second stage, the FHR is auscultated every 5 minutes or soon after every other contraction. Contractions are monitored by manual palpation over a period of 10 minutes to determine the frequency and duration. The frequency of intermittent auscultation (IA) was recommended on the basis that there was no difference in fetal and neonatal outcome in randomized studies that compared IA every 15 minutes for 1 minute after a contraction in the first stage and every 5 minutes in the second stage with EFM. Ideal auscultation practice should be listening and recording the baseline FHR on admission (cross-checked against the maternal pulse rate) followed by auscultation with the FMs to demonstrate an acceleration and soon after a contraction to confirm that there are no decelerations. Technological advances have made it possible for a hand-held Doptone to display the digital FHR and convert the information to produce a CTG on a light-emitting diode (LED) screen, which can be seen, stored within the device and reviewed later if the need arises ( Fig. 11.9 ).

The clinical guidelines for the use of EFM have been produced by the National Institute for Health and Clinical Excellence in the UK, Australia and New Zealand College of Obstetricians and Gynaecologists and by similar bodies in the United States and Canada, as well as by the International Federation of Gynaecologists and Obstetricians (FIGO). They have great similarities and minor differences that are unlikely to influence clinical outcome. Admission CTG or routine CTG using electronic monitoring is not recommended for women classified as low risk. However, the woman’s wishes should be respected after appropriate counselling. This may be that the woman wishes or not the use of admission CTG or continuous CTG. The specific indications for continuous EFM are listed in Table 11.1 .

Table 11.1

Indications for the use of continuous electronic fetal monitoring

Maternal	Fetal
Previous caesarean section	Fetal growth restriction
Pre-eclampsia	Prematurity
Post-term pregnancy	Oligohydramnios
Prolonged rupture of the membranes	Abnormal Doppler artery velocimetry
Induced labour	Multiple pregnancy
Diabetes	Meconium-stained liquor
Antepartum haemorrhage	Breech presentation
Other maternal medical diseases

Fetal cardiotocography

EFM enables continuous monitoring of the FHR and the frequency and duration of uterine contractions. The heart rate of the fetus is usually calculated using a Doppler ultrasound transducer, which is applied externally to the maternal abdomen. The signals that are detected are those of cardiac movement, and what is measured is the time interval between cardiac cycles. Traditionally, this is converted to heart rate. The heart rate can also be measured from the RR wave intervals obtained from the fetal electrocardiogram (ECG) by direct application of an electrode to the presenting part.

Uterine activity is recorded either with a pressure transducer applied over the anterior abdominal wall between the fundus and the umbilicus or by inserting a fluid-filled catheter or a pressure sensor into the uterine cavity through the cervical canal ( Fig. 11.10 ). External tocography gives an accurate measurement of the frequency and duration but only relative information of intrauterine pressure. Accurate measurements of pressure need an intrauterine catheter or transducer, and this is not used as a routine in most centres due to lack of evidence of its clinical benefit.

Baseline heart rate

The definition of normality in the pattern of the FHR is easier than defining what is abnormal. The normal heart rate varies between 110 and 160 beats/min ( Fig. 11.11 ). A rate faster than 160 is defined as fetal tachycardia, and a rate less than 110 is fetal bradycardia .

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