Syntocinon

The management of labour used to be largely expectant--"wait and see" or "never let the sun set twice on a labouring woman," implying that a labour taking up to 48 hours was acceptable. Labours of this length are often emotionally traumatic for women, may hide hazards to the fetus, and are very demanding on staff resources. In the 1960s, '70s, and '80s O'Driscoll and colleagues promoted "active management" of labour for women in their first labour. This management emphasised:

* A policy of non-interference for women not definitely in labour;

* Regular assessment of cervical dilatation;

* Early intervention, with artificial rupture of membranes and infusion of Syntocinon if labour progressed more slowly than 1 cm/h; and

* One to one care with a skilled birth attendant.

Subsequent studies showed that, although this approach reduces the length of labour by a small amount, the only component with a clear benefit in promoting spontaneous vaginal birth is the continuous presence of the birth attendant. Women have declared their intolerance of long labours, however, by increasingly requesting delivery by caesarean section. In many major maternity units in the developed world, the rate of caesarean sections is now 16% or higher. In the United Kingdom this process has been accelerated by the Changing Childbirth initiative, which emphasises the importance of maternal preferences.

Commonest monitoring techniques

Currently, the most common recommendations for monitoring progress in labour are measuring the descent of the fetal head and a vaginal examination of cervical dilatation every four hours. The rate of dilatation below which augmentation by Syntocinon infusion is recommended varies from 1 cm/h (the original O'Driscoll recommendation, resulting in augmentation rates in first labours of 40-50%) to 0.5 cm/h (leading to augmentation rates of about 15%). The mother's condition is assessed by repeating blood pressure measurements, recording her temperature, and checking hydration by the volume of urine and ketone concentration in the urine produced. These variables are recorded on a combined flow chart (a partogram).

Electronic fetal heart rate monitoring

The fetal condition is monitored by assessment of the fetal heart rate, either by intermittent auscultation or by continuous electronic monitoring. The former is performed at intervals varying from every 2 hours to every 15 minutes, depending on the circumstances--for example, more frequently if there is meconium staining of the amniotic fluid, or during the second stage. Auscultation is best performed at the end of a contraction, to detect late decelerations (transient decrease in heart rate occurring at or after the end of a uterine contraction), but at this time the fetal heart is often difficult to hear. Use of a portable Doppler fetal heart detector has revolutionised this procedure, making it possible to count the fetal heart rate easily with the woman in any position; there are even waterproof machines for use in birth pools. A fetal heart rate above 150 beats/minute or below 110 beats/minute for more than a few minutes requires further investigation by continuous electronic fetal heart rate monitoring. Any slowing of the heart rate by more than 15 beats/minute after contractions is also an indication for electronic monitoring.

Drawbacks

In recent years continuous electronic fetal heart rate monitoring has had a bad press. This is due at least partly to a false expectation that it could reveal all about fetal condition during labour. In fact, it is a good method for screening for umbilical cord compression, fetal hypoxia, and acidosis. It has a high sensitivity for these problems, but the main drawback is its high false positive rate. During the first stage of labour about a fifth of normal fetuses will have a fetal heart rate pattern that is not normal; most abnormalities reflect stress--for example, temporary cord compression or hypoxia--rather than distress.

To reduce unnecessary operative delivery for erroneous suspicions of acidosis, it is essential that electronic fetal heart rate monitoring is supplemented by fetal blood sampling with pH and base deficit measurement. Unfortunately, this technique is time consuming and is therefore used regularly in only about half the maternity units in Britain. Other drawbacks to electronic monitoring are:

* Its unreliability in detecting intrapartum infection, which sometimes causes a fetal tachycardia (most tachycardias, however, are due to maternal fever, common in labour, especially in association with epidural analgesia); and

* Its inability to predict acute trauma, such as shoulder dystocia.

A further problem is that the interpretation of fetal heart rate patterns is notoriously subjective. Although specialists can reliably distinguish abnormal from normal patterns, this is much more difficult for beginners, who despite their lack of experience are often overconfident. Even the specialists find some patterns difficult to interpret. Although late decelerations nearly always indicate some degree of hypoxia, fetal reserve is variable, and the ability of the fetus to cope over a period of time can be assessed only with serial blood sampling to give blood gas and pH estimation.

Passage of meconium

The second traditional indicator of fetal distress is the passage of meconium by the fetus during labour. Meconium is the contents of the fetal bowel, and presence of bile acids and salts renders meconium very corrosive. Normal fetuses usually pass meconium only after they have been born. The stimulus for its passage is probably activation of massive sensory input, a part of the "fight, flight, and fright" reaction. Some fetuses pass meconium in response to stress while still in utero--most commonly, during labour. The proportion of fetuses passing meconium rises from less than 4% before 34 completed weeks to over 30% at 42 weeks. Having meconium in the amniotic fluid is relatively harmless for the fetus so long as it does not inhale the contaminated liquor. The stimulus for gasping in utero is not known but may well include acute hypoxia.

The combination of meconium in the amniotic fluid and gasping leads to the meconium aspiration syndrome, still a cause of neonatal mortality in Britain. The appearance of meconium during labour does not in itself indicate fetal distress as it is often associated with healthy fetuses, so provided the fetal heart rate remains normal, there is no increased likelihood of fetal acidosis. If the fetal heart rate becomes abnormal, however, the potential for meconium aspiration is increased.

New techniques

Several new methods of fetal assessment, such as fetal electrocardiographic wave form analysis, fetal pulse oximetry, and near infrared spectroscopy for assessment of acidosis, are technically difficult to implement. They are still research tools. New microsampling methods of measuring lactate in the fetal blood, however, have the potential for assessing fetal acid base reserve in a way that is simpler, cheaper, and more reliable.

Preventing errors

Confidential inquiries into perinatal death indicate that in 60% of labour cases there is a preventable element related to incorrect assessment of fetal monitoring. Studies of the causes of perinatal death and cerebral palsy have suggested a 50% and 25% rate respectively of possibly avoidable errors related to fetal monitoring. It seems that there is more to be gained at the moment by improved use of current technology than by trying to implement completely new methods of monitoring.

Leading areas of clinical error

According to data from the confidential inquiry into stillbirths and deaths in infancy for England and Wales 1994-5, the five leading areas of clinical error, in decreasing rank order are:

* Assessment of fetal condition during labour, particularly with regard to the use of electronic fetal heart rate monitoring and fetal blood sampling;

* Recognition of risk during labour;

* Management of labour;

* Assessment of risk factors before labour; and

* Management of delivery.

These were the leading areas found among 873 deaths during labour of normal babies ([is greater than] 1500 g birth weight). Better care would have improved outcome in 52% of cases and might have done in another 25%.

The data in the table showing rates of oxytocin augmentation and incidence of caesarean section are taken from O'Driscoll K et al (Obstet Gynaec 1984;63;485-90). The graph showing results of the meta-analysis is adapted from Thornton J et al (BMJ 1994;309:366-9). The graph showing the distribution of caesarean sections is adapted from the Statistical Bulletin NHS Maternity Statistics (London: Stationery Office, 1997). The cardiotocograms are adapted from Fetal Heart Rate Monitoring--A Practical Guide (Oxford: Oxford University Press, 1993). The fetal pulse oximetry recording is adapted from Johnson et al (Br J Obstet Gynaecol 1991 ;98: 36-41). The graph showing results of infrared spectrometry is adapted from Peebles et al (Am J Obstet Gynecol 1992;166:1369-73).

Philip Steer is professor of obstetrics and consultant obstetrician at the Imperial College School of Medicine, Chelsea and Westminster Hospital, in London.

The ABC of Labour Care is edited by Geoffrey Chamberlain, emeritus professor of obstetrics and gynaecology at the Singleton Hospital, Swansea. It will be published as a book in the summer.

BMJ 1999;318:858-61

Accepted indications for continuous electronic fetal heart rate monitoring in labour

Computerised analysis of fetal heart rate patterns

* Computerised analysis of fetal heart rate patterns in labour is now almost possible, as recent trials of such systems have been encouraging

* Computer based teaching programmes offer a real chance of improving the general standard of interpretation

Advantages of measuring lactate over pH estimates in fetal blood sampling to detect a hypoxic fetus(*)

* Less dilatation of the cervix is needed

* Fewer scalp punctures are needed

* Sampling technique is faster

* Less fetal blood is needed (5[micro]l v 35[micro]l)

(*) From Westgren M et al (BrJ Obstet Gynaecol 1998;105:29-33)

Key references

* Department of Health. Changing childbirth. London: HMSO, 1992.

* O'Driscoll K,Jackson RJA, GallagherJT. Prevention of prolonged labour. BMJ 1969;ii:477-80.

* O'Driscoll K, StrongeJM, Minogue M. Active management of labour BMJ 1973;3:135-7.

* O'Driscoll K, Foley M, MacDonald D. Active management of labour as an alternative to caesarean section for dystocia. Obstet Gynecol 1984;63:485-90.

* Westgren M, KrugerK, Ek S, Gunnaralt C, Kublickas M, Naka K, et al. Lactate compared with pH analysis at fetal scalp blood sampling: a prospective randomised study. Br J Obstet Gynaecol 1998;105:29-33.

* Spencer J, Ward H. Intrapartum fetal surveillance. London: RCOG Press, 1993.

* Ingermarsson J, Ingermarsson H, SpencerJ. Fetal heart rate monitoring. A practical guide. Oxford: Oxford University Press, 1993.

* Confidential Enquiry into Stillbirths and Deaths in Infancy. London: Maternal and Child Health Research Consortium, 1998.

COPYRIGHT 1999 British Medical Association
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