Chapter Contents
Introduction 207
Intrapartum assessment and management 208
Diagnosis of labour 208
Interventions during labour 208
Electronic fetal heart rate monitoring 209
Baseline rate 209
Baseline variability 210
Accelerations 210
Decelerations 210
Early decelerations 210
Variable decelerations 211
Late decelerations 212
Preterm fetus 212
Sinusoidal and pseudosinusoidal fetal heart rate patterns 212
Pseudosinusoidal fetal heart rate patterns 212
Fetal scalp blood sampling 212
Umbilical cord blood sampling 214
Delivery of the baby 214
Shoulder dystocia 215
Induction of labour 215
Breech presentation 215
Multiple pregnancy 216
Other high-risk situations for the fetus 216
Preterm infants 216
Preterm labour 217
Preterm prelabour rupture of the membranes 217
Tocolysis 217
Antenatal steroid therapy in preterm labour 218
Introduction
There is increasing evidence that safe high-quality maternity services are best provided by multidisciplinary teams led by fully trained obstetricians and midwives working with neonatologists, anaesthetists and many other specialist care providers. Safer Childbirth (Royal College of Obstetricians and Gynaecologists ( ) and Standards for Maternity Care ( ) have set the standards by which this care may be best achieved. The aim of modern obstetric management is the early identification of complicated pregnancies and those with abnormal placental function ( ), so that medical care may be focused on those women. Women with low-risk pregnancies should have their care provided by midwives ( ).
The aim of this chapter is to outline the intrapartum assessment of the fetus who is thought to be normal. Antenatal assessment of fetal well-being is also very important and is covered in detail in other chapters of this book.
Common complications that occur in labour and the management strategies will be covered in this chapter. Clearly, this account cannot be exhaustive: the intention is to concentrate on aspects of obstetric care of relevance to the neonatologist. Further reading and useful weblinks are included at the end of the chapter.
Intrapartum assessment and management
This section begins by discussing the mechanism of normal labour and the use of Syntocinon to correct slow progress in labour. Fetal response to labour and ways of assessing intrapartum fetal well-being are discussed, as are the different modes of delivery and why any particular way is chosen.
Diagnosis of labour
Recognition of the onset of labour determines all subsequent management objectives. The onset of labour is a complex physiological process and cannot easily be defined by a single event. Although labour is a continuous process, it is convenient to divide it into stages in order to ensure that the woman and the staff providing her care have an accurate and shared understanding of the concepts, enabling them to communicate effectively.
Latent first stage of labour
The onset of labour is a transition period from ‘not in labour’ to the diagnosis of active labour; this period is called the latent phase. In a woman having her first baby this period of time can last for several days, whereas in a multiparous patient it frequently does not occur at all. During this time there are painful contractions, with gradual cervical change, including effacement (shortening) of the cervix and dilatation up to 3–4 cm. During this period women are encouraged to stay at home, mobilise and not to focus on the contractions.
Established first stage of labour
The diagnosis of labour is made when there is progressive cervical dilatation in the presence of regular painful contractions and descent of the presenting part.
Once labour has been established, regular examinations of the cervix are performed (NICE guidelines ( ) on intrapartum care suggest 4-hourly), and the rate of cervical dilatation is plotted against time on a graph described as a partogram. The average rate of cervical dilatation and the construction of a partogram against which progress could be charted were established by studying a very large number of women in normal labour ( ); women falling behind the average rate of progress, determined as a rate of cervical dilatation at 1 cm per hour, are readily identified by charting their progress on the partogram, and following medical review they can be considered for augmentation of labour with Syntocinon.
This charting of labour progress led to ‘active management of labour’ ( ; ; ), whereby women falling outside ‘normal’ progress automatically had augmentation of labour. It is now clear, however, that the active management of labour does not reduce the rate of caesarean section (CS) or increase spontaneous vaginal birth. In addition the injudicious use of Syntocinon in the presence of fetal compromise has considerably worsened the condition of many babies at birth. It is clear that regular training and updating of midwifery and medical staff are mandatory in units where Syntocinon is routinely used to ensure that the hypoxic fetus is recognised early and timely intervention undertaken to protect the baby.
Second stage of labour
Once the cervix is fully dilated (second stage), progress is defined as descent of the presenting part through the birth canal. This is judged by hourly vaginal examinations. In the absence of an epidural, the usual limits of duration for pushing are 60–90 minutes for a woman having her first baby and 30–60 minutes for multiparous women. These recommendations have some support, in that fetal hypoxia and acidaemia increase progressively during the second stage ( ; ; ; ). However, in recent years, with the increasing use of epidural analgesia ( ), allowing more time in the second stage before starting active pushing has been shown to improve the chance of vaginal delivery ( ; ) without a major deterioration in fetal pH. Nevertheless, the need for operative assistance in the presence of an epidural remains significantly increased ( ), and many consider one additional hour sufficient to minimise this possibility ( ). NICE recommends that in nulliparous women birth should be expected to occur within 3 hours of the start of the active second stage ( ). A diagnosis of delay in the active second stage should be made after 2 hours of active pushing in a primiparous and 1 hour in a multiparous woman. Unless delivery is imminent the usual action would be to ask for a medical review to assess the condition of both the mother and her baby and to determine whether an operative vaginal birth is required.
Interventions during labour
Amniotomy and augmentation of labour with an intravenous infusion of Syntocinon are interventions that are regularly undertaken when labour progress is deemed to be slow.
Amniotomy
Active management of labour includes routine amniotomy (membrane rupture) if the cervix fails to dilate 2 hours following the diagnosis of labour ( ; ; ). While there is some evidence ( ) that there may be a reduction in the length of the second stage of labour in women having their first baby, earlier amniotomy is associated with a higher incidence of caput formation and moulding of the fetal head ( ) and an increased incidence of early uniform fetal heart rate (FHR) decelerations and a significantly lower median umbilical artery pH at birth (albeit still within the normal range) ( ). These findings can be explained on the basis of increased uterine activity, greater head compression and (probably most importantly) cord compression. In the presence of an abnormal FHR pattern membrane rupture may provide additional information if meconium is present, although 20% of normal women will have meconium present in the amniotic fluid ( ). Rupture of the membranes is also required before fetal blood sampling (FBS) or application of a fetal scalp electrode.
Meconium
The incidence of meconium in the liquor increases with advancing gestational age ( ) The overall reported incidence is 12%, with an incidence of less than 10% at 38 weeks to virtually 100% of pregnancies at 42 weeks complicated by meconium staining of the liquor. The prelabour passage of meconium may reflect a previous transient fetal stimulation, possibly hypoxia, and infection and thyrotoxicosis are rare causes. The passage of meconium in utero is associated with significant increases in perinatal morbidity and mortality ( ; ) as the aspiration of meconium into the lungs during intrauterine gasping, or when the baby takes its first breath, can result in a life-threatening disorder known as meconium aspiration syndrome ( ).
Occasionally green ‘meconium-stained’ liquor is actually bile-stained, due to fetal vomiting associated with intestinal obstruction. Thus, meconium remains an indication for continuous electronic FHR monitoring (EFM) during labour, and the presence of meconium lowers the threshold for making a diagnosis of fetal hypoxia if FHR abnormalities occur.
Effects of oxytocin
The aim of augmentation of labour with Syntocinon infusion is to achieve optimal uterine activity with a maximum contraction frequency of 4–5/10 minutes. Uterine perfusion decreases during contractions as a result of a decrease in blood flow to the intervillous space ( ; ). Fetal oxygenation remains unaffected, as long as there is sufficient time for relaxation between contractions to allow reperfusion of the placental bed ( ). Nevertheless, in clinical practice the use of Syntocinon is associated with an increased incidence of FHR decelerations and therefore vigilance is essential, and requires continuous high-quality recording of the FHR ( ).
Electronic fetal heart rate monitoring
Several randomised controlled trials have suggested that continuous EFM confers no advantage over intermittent auscultation for normal, uncomplicated labours ( ; ). When continuous monitoring is indicated the cardiotocogram (CTG) must be interpreted in the context of the clinical picture.
Recently produced evidence-based guidelines on the use and interpretation of the CTG in intrapartum fetal surveillance have been produced (NICE 2010). This guideline categorises FHR features into ‘reassuring’, ‘non-reassuring’ and ‘abnormal’ groups ( Table 12.1 ), enabling classification of the CTG trace as ‘normal’, ‘suspicious’ or ‘pathological’ (two non-reassuring features, or one abnormal feature) ( Table 12.2 ). ‘Suspicious’ traces can be managed conservatively but ‘pathological’ traces demand either a FBS or delivery.
| FEATURE | BASELINE (bpm) | VARIABILITY (bpm) | DECELERATIONS | ACCELERATIONS |
|---|---|---|---|---|
| Reassuring | 110–160 | ≥5 | None | Present |
| Non-reassuring | 100–109 | <5 | Typical variable decelerations with over 50% of contractions, occurring for over 90 minutes. Single prolonged deceleration for up to 3 minutes | The absence of accelerations with otherwise normal trace is of uncertain significance |
| Abnormal | <100 >180 Sinusoidal pattern ≥10 minutes | <5 for 90 minutes | Either atypical variable decelerations with over 50% of contractions or late decelerations, both for over 30 minutes. Single prolonged deceleration for more than 3 minutes |
| CATEGORY | DEFINITION |
|---|---|
| Normal | An FHR trace in which all four features are classified as reassuring |
| Suspicious | An FHR trace with one feature classified as non-reassuring and the remaining features classified as reassuring |
| Pathological | An FHR trace with two or more features classified as non-reassuring or one or more abnormal categories |
Baseline rate
This is the mean FHR in beats per minute (bpm) determined over a 5–10-minute interval, when stable in the absence of accelerations and decelerations. The normal baseline FHR lies between 110 and 160 bpm at term ( Table 12.1 ).
Fetal tachycardia
Acute rises in FHR in labour may reflect an increase in catecholamine secretion and indicate an early adaptive response to fetal hypoxia before the development of fetal acidaemia. Chorioamnionitis should always be suspected. Epidural analgesia can cause maternal fever and fetal tachycardia ( ). Rarely a fetal tachyarrhythmia may be recognised for the first time in labour. Fetal tachycardia above 180 bpm has traditionally been regarded as a sign of fetal compromise, particularly if found in association with other abnormal FHR patterns when the likelihood of acidosis is significantly increased ( Fig. 12.1 ). FBS or delivery then becomes a priority.
Fetal bradycardia
A persistent low baseline between 100 and 110 bpm can be seen in some postdate pregnancies and in fetuses whose mothers are taking drugs such as beta-blockers. Fetal heart block is another possibility.
Acute bradycardia below 100 bpm can occur following vaginal examination and full dilatation of the cervix and after epidural top-ups. An acute fall in FHR indicates an acute interruption of oxygen delivery, secondary to maternal hypotension/aortocaval compression, umbilical cord compression, cord prolapse, placental abruption or, rarely, a ruptured uterus ( Fig. 12.2 ). Acidaemia develops within 10–15 minutes and will continue to progress unless the situation is corrected. If the bradycardia fails to recover after appropriate treatment, immediate delivery is necessary ( ). However, if the baseline FHR returns to normal and there are no other abnormal FHR features, conservative management is appropriate. Fetal bradycardia in association with other FHR abnormalities can be sinister. The worst combination of FHR abnormalities described has been progressive bradycardia associated with absent FHR variability, which is regarded as a terminal response of a dying fetus ( ) ( Fig. 12.2 ).
Baseline variability
This refers to oscillations of the recorded baseline FHR. During periods of fetal activity, baseline variability is usually ≥5 bpm (<25 bpm) and there should be two or more accelerations in a 20-minute period ( Fig. 12.3 ). Episodes of low variability, often less than 5 bpm, are associated with the quiet fetal behavioural state ( ). Such physiological episodes do not last more than 40 minutes. Excessive variability (>25 bpm) is an early adaptive response to fetal hypoxia, and in isolation is not found to be predictive of fetal acidaemia. Commonly, however, abnormalities of the baseline variability are seen in conjunction with other FHR abnormalities. In such cases further tests of fetal well-being are appropriate.
Accelerations
An acceleration is a transient rise in FHR of at least 15 bpm, which lasts for more than 15 seconds. If the rate remains raised then this may be considered tachycardia. It has been known for some time that acceleration is the only pattern not related to fetal acidaemia ( ).
Decelerations
A deceleration is a transient fall in FHR. Decelerations are not part of the normal CTG appearance in term fetuses. In general, decelerations should be considered transient bradycardias. Fetal acidaemia only occurs after a considerable reduction in fetal oxygen delivery.
Early decelerations
These are decelerations in which the trough of the decrease in the FHR is synchronous with the peak of the uterine contraction and does not fall below 90 bpm. They are rare, occur when the head is deeply engaged in the late first stage or early second stage and are generally benign. If the early decelerations persist in the presence of a delayed second stage or there are other abnormalities of the FHR, FBS or delivery is indicated.
Variable decelerations
A variable deceleration ( ) is one where the morphology of the deceleration and/or the timing in relationship to the contraction varies ( Figs 12.4 and 12.5 ). Typical variable decelerations are a fetal response to cord compression where the fetus is coping with labour; ) suggests that they only become a non-reassuring feature if they are present for greater than 50% of contraction over a 90-minute period. Atypical variable decelerations are an abnormal feature on a CTG and suggest fetal acidosis; if they occur for greater than 50% of contractions over a 30-minute period then either FBS or delivery is mandatory.
Late decelerations
These are decelerations in which the trough of the decrease in the FHR occurs after the peak of the uterine contraction. They are associated with fetal acidaemia and when present the fetus must either have further assessment by FBS or be delivered within 30 minutes. Late decelerations, particularly in the setting of other FHR abnormalities, suggest fetal hypoxia secondary to uteroplacental insufficiency. The characteristic changes associated with chronic placental failure include loss of accelerations, reduced baseline variability and the onset of recurrent decelerations ( Fig. 12.4 ).
Preterm fetus
The interpretation of the FHR pattern of the preterm fetus in labour is similar to that of its term counterpart, with some subtle differences. The baseline is higher and the variability is often less. Accelerations occur less frequently and are less marked. The differentiation between quiet and active sleep patterns may not be evident until 32 weeks’ gestation. Small brief (20-second) decelerations are often seen and are not considered significant.
Sinusoidal and pseudosinusoidal fetal heart rate patterns
The classical CTG pattern in severe fetal anaemia is described as ‘sinusoidal’ ( Fig. 12.6 ). This is a preterminal pattern which is rarely seen. Five rigid criteria must be fulfilled to make the diagnosis ( ):
- 1
a stable baseline FHR of 120–160 bpm, with regular oscillations
- 2
an amplitude of 5–15 bpm
- 3
a frequency of 2–5 cycles/min
- 4
absent short-term variability
- 5
no areas of normal FHR variability or reactivity.
Pseudosinusoidal fetal heart rate patterns
Pseudosinusoidal FHR patterns (vaguely defined as undulatory waveforms), in contrast, are common and usually benign. They are strongly associated with the use of pethidine and epidural analgesia and are also seen with fetal sucking movements. Such patterns will generally improve with time.
From the review of FHR patterns it is clear that no single abnormal pattern reliably predicts fetal outcome. Comprehensive evaluation of all the FHR characteristics must be integrated into the clinical scenario before decisions can be made on management. Of most importance is the influence of prelabour placental insufficiency on fetal tolerance to interruptions in oxygen delivery during labour. Acidaemia develops more rapidly in cases of intrauterine growth restriction ( ).
The future of FHR monitoring requires further understanding and acceptance of the need for a more physiological approach to interpretation ( ).
Fetal scalp blood sampling
Clinical trials have shown that there is an increased risk of CS if CTG is used without FBS. This has led NICE to recommend that EFM should not be used without facilities for FBS ( ). Fetal scalp sampling involves taking a small sample of blood from the fetal scalp. It is a difficult process for both the mother and the doctor as it is uncomfortable and can be technically difficult to perform, particularly if the cervix is less than 4 cm dilated. The mother is positioned in the left lateral position and an amnioscope (a specially designed speculum) is inserted into the vagina. Under direct vision the skin of the fetal scalp is punctured and a capillary tube of fetal blood is collected and then analysed in a blood gas analyser.
The normal values for pH in fetal scalp blood are shown in Table 12.3 . If the pH is 7.2 or less, immediate delivery is indicated. If the pH is greater than 7.2, it is appropriate to continue with the labour and repeat the test, unless the situation deteriorates, necessitating earlier intervention. The rate of fall of the fetal scalp pH is as important as each absolute value. This must be integrated into the clinical picture.
| FETAL BLOOD SAMPLE RESULT (pH) | INTERPRETATION OF THE RESULTS |
|---|---|
| ≥7.25 | Normal FBS result |
| 7.21–7.24 | Borderline FBS result |
| ≤7.20 | Abnormal FBS result |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
