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The origins of cerebral palsy -- a consensus statement* The Australian and New Zealand Perinatal Societies
MJA 1995; 162: 85-90
Introduction -
Definition -
Prevalence -
Causes -
Timing the onset of pathological brain lesions -
Imaging of the brain -
Can obstetric care prevent cerebral palsy? -
Fetal distress -
Birth asphyxia -
Neonatal encephalopathy -
Does cerebral palsy ever originate in labour? -
Fetal response to acute hypoxia -
Causation and fault -
Expert witnesses -
Alternatives to litigation -
Long term support services -
Conclusions -
References -
Authors' details
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| Introduction |
There is a crisis affecting maternity care in many countries. Both
caesarean section rates and medical defence premiums are
increasing. New options for the care of pregnant women (e.g.,
birthing units) may fail because midwives, general practitioners
and smaller hospitals may be unable to afford adequate insurance to
continue their services.1
The crisis is fuelled by widespread beliefs that cerebral palsy is often caused by injuries sustained during labour and birth and that cerebral palsy may therefore be the result of inappropriate obstetric care. There is now considerable evidence to suggest that these beliefs are unfounded. A conference of Australian and New Zealand specialists in this area was convened to review the relevant literature and offer a consensus statement to help parents, counsellors, lawyers and health professionals understand what is known and what is not known about the origins of cerebral palsy. | |||||||||||
| Definition | Cerebral palsy is not a single entity but covers neurological impairments characterised by abnormal control of movement or posture resulting from abnormalities in brain development or an acquired non-progressive cerebral lesion. | |||||||||||
| Prevalence | Cerebral palsy is the most common physical disability in childhood, occurring in about 2-2.5 per 1000 children born. The frequency of cerebral palsy has not changed over the last 40 years, despite a fourfold drop in both perinatal and maternal mortality. In some countries there is an increase in the occurrence of cerebral palsy, attributable mostly to the increased survival of very low birthweight infants. | |||||||||||
| Causes |
There are many antenatal factors that may lead to cerebral palsy and
often there may be several contributing factors.2,3 Examples are
shown in Box 1. There are also strong associations between cerebral
palsy and intrauterine growth restriction, antenatal death of
co-twin/triplet and extreme prematurity.
The fetus is designed to withstand the stress of labour, which usually involves a reduction in the amount of oxygen in the blood (hypoxaemia) and the amount of blood reaching the brain (ischaemia) during passage through the birth canal. If these reductions are too great, a normal fetus is more likely to die than survive with cerebral palsy.4 These normal reductions of blood supply and oxygen can compound the detrimental effects of any chronic hypoxia already experienced during the antenatal period.4 Cerebral palsy occurring after birth is also uncommon and is caused by, for example, complications of prematurity, untreated rhesus disease (kernicterus), meningitis, accidents or near-drowning.3 | |||||||||||
| Timing the onset of pathological brain lesions |
It should be clearly stated that, currently, fetal brain development
(or maldevelopment) cannot be monitored during pregnancy. Only
examination of the brain at autopsy can identify the full extent of
injury in some cases. In other cases of cerebral palsy no pathological
lesion is identifiable. The neuropathological lesions leading to
cerebral palsy are various and include maldevelopments (cerebral
dysgenesis), germinal matrix-intraventricular haemorrhage,
cerebellar haemorrhages, grey matter damage, white matter damage
(periventricular leukomalacia), hypoglycaemic neuronal injury,
thromboembolic injury (including vasculitis secondary to
infection) and kernicterus.
The immature brain has only a limited number of ways of responding to acute or chronic injury and these essentially consist of neuronal and white matter loss and glial proliferation. These changes occur over many days and weeks. They may later be modified by secondary changes such as posthaemorrhagic or postinflammatory hydrocephaly or white matter atrophy. By the time a child presents with cerebral palsy during the first years of life, the neuropathological effects of any hypoxic-ischaemic injury or other injury will have become modified by these changes and by further postnatal brain development. Even if that child were to die during its first year and the brain was made available for expert examination, it would be impossible, on this basis, to determine the exact timing of the original neurological insult. Recent suggestions that the condition of the placenta could be used as a surrogate marker of antepartum fetal injury are based largely on anecdotal argument and have not yet been fully evaluated; such techniques are fraught with observer and sampling bias. |
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| Imaging of the brain |
Antenatal ultrasound scans may detect gross brain changes, but a
normal scan does not exclude antenatal neuropathology. Few infants
undergo brain imaging, either because there is no clinical suspicion
that cerebral palsy may develop or because there are no imaging
facilities available. A neonatal ultrasound examination may not
demonstrate longstanding microscopic changes but can detect major
acute lesions or secondary changes. Acute lesions may appear as
periventricular flare, oedema and intracranial haemorrhage.
Periventricular and caudothalamic notch cysts, porencephaly,
parenchymal calcification and intraventricular adhesions may also
be demonstrated in the early neonatal period and imply events
occurring more than two weeks previously.
The period from 26 to 34 weeks' gestation is critical for neurodevelopment. The patterns of brain injury, and therefore imaging features, are similar in fetuses and neonates, and late investigations cannot separate brain injury occurring in utero from perinatal or postnatal events. Magnetic resonance imaging of limited numbers of cerebral palsy patients5,6 suggests that the adverse neurodevelopmental event occurs prenatally in up to 50% of cases. |
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| Can obstetric care prevent cerebral palsy? |
If better obstetric care could prevent cerebral palsy then lower
rates of cerebral palsy would be associated with good obstetric care
rather than with bad obstetric care. There is very little good
evidence for this supposition. Several decades ago, new
technologies such as electronic fetal monitoring were introduced
into obstetrics, without adequate assessment by randomised trials.
It was assumed that early detection of fetal distress would allow
early delivery (e.g., by caesarean section), thus avoiding damage to
the fetal brain and cerebral palsy. Although it is probable that some
perinatal deaths have been prevented by such techniques, there is no
evidence that they have reduced the prevalence of cerebral palsy,
despite increased use of fetal monitoring and rising caesarean
section rates.7 In view of the likely
antenatal origins of most cases of cerebral palsy, this is not
surprising. However, the mistaken belief that birth injury is a major
cause of cerebral palsy may have stemmed from:
These factors may lead to the assumption that the fetus was healthy before labour and that it was only in labour or at birth that problems occurred. However, events causing or predisposing to cerebral palsy may occur from conception onwards, as shown in the Figure. Any one event or any combination of events could be the cause of the cerebral palsy. |
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|
The term fetal distress is imprecise and
non-specific.9 No antenatal or intrapartum
monitoring technique can clearly tell whether a fetus is unhealthy or
whether the condition is acute or chronic. Tests such as electronic
fetal heart rate monitoring poorly predict fetal outcome. Up to 79% of
fetal heart rate traces during labour show some type of variation that
has been described as abnormal,8 but the vast majority of such
infants are born without signs of perinatal asphyxia or cerebral
palsy.10 Clinical signs and test
results predict only the possibility of distress and, as
distress has no agreed definition in this context, it is preferable to
avoid the term fetal distress and instead describe the observed signs
or the variation in the test results.
A normal fetal heart rate is generally predictive that there is no acute hypoxaemia, but variations from the normal pattern are not good predictors of hypoxaemia. Even prolonged late decelerations with reduced variability have a less than 50% chance of being associated with major fetal acid-base changes, which themselves are only poorly correlated with cerebral palsy.11 Similarly, meconium-stained liquor is a common finding in labour, but only a minority of babies from these labours are born with a low umbilical arterial blood pH. Finally, Illingworth has suggested that there is an undue readiness to ascribe brain damage to umbilical cord problems.12 Earn found a loop around the neck of the fetus in 23% of 5676 consecutive births, without significant effect on fetal outcome, except for one neonatal death where the cord was wound eight times around the baby's neck.13 | ||||||||||||
| Birth asphyxia |
Birth asphyxia is not a well-defined term.14 It implies some sort of
dysfunction resulting from a lack of oxygen supply to the baby's
tissues during the birth process. The term should not be used
clinically because of the difficulty in ascribing clinical signs and
symptoms in the neonate to an event during birth. Low pH and/or low
Apgar scores at birth are supportive evidence of asphyxia but should
not be used alone to make the diagnosis.15,16 Until more
information is available, perinatal asphyxia is the preferred term
to describe a neonate in whom there is:
|
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| Neonatal encephalopathy | Neonatal encephalopathy is a clinical syndrome of signs suggesting neonatal neurological abnormality. It has many causes and intrapartum hypoxia cannot be considered as a possible cause unless encephalopathy is evident within 24 hours of delivery. The extent of encephalopathy is a reasonable predictor of neurological outcome. Levene et al. graded the signs and recorded the varied outcomes as shown in Box 2.18 | |||||||||||
| Does cerebral palsy ever originate in labour? | Most infants who develop cerebral palsy are born from uncomplicated pregnancies and are delivered without signs of fetal heart rate abnormalities. They do not have low Apgar scores or acidosis at birth or any abnormal neurological signs in the neonatal period.19,20 Two major studies of children with cerebral palsy have been reported in which their labour, delivery and neonatal records were in agreement in finding that, for 90%-94%, their disability could not be related to intrapartum hypoxia.20-22 This does not mean that in 6%-10% of labours hypoxia beginning in labour is the cause of cerebral palsy. In cases in which severe intrapartum hypoxia was documented, it may not have been preventable and earlier delivery may not always have been possible. Pre-existing neurological deficit can contribute to intrapartum hypoxia, or be associated with chronic hypoxia.23 It is our opinion that the lesions causing cerebral palsy are rarely initiated in labour and are rarely preventable.24,25 What little evidence exists suggests that less than 2% of cerebral palsy could be attributed to suboptimal intrapartum care.26 It is the opinion of this conference that this figure could be lower. | |||||||||||
| Fetal response to acute hypoxia |
The healthy fetus has some remarkable defence mechanisms to cope with
reductions in oxygen that might occur in labour. The human fetus may
have longstanding mild or moderate hypoxaemia24 and, in
hypoxic conditions, can sustain life without neurological damage
for much longer periods than an adult. This is principally because
fetal haemoglobin releases more of the available oxygen to the fetal
tissues than adult haemoglobin and, secondly, when acutely stressed
the fetus can redirect nearly all its blood supply to its brain and the
placenta. It is difficult to estimate the duration of hypoxia before
birth. There may be a period of up to several hours with cardiographic
changes without acidaemia in cord blood.27,28
In experiments, the sheep fetus has been found to adapt to prolonged hypoxaemia, tolerating up to eight hours of mild ischaemic hypoxia before any signs of mild damage to vital systems.29 These fetuses can maintain oxygen delivery to the brain over a wide range of blood oxygen concentrations. Once the lower limit of compensation is reached, however, the fetus tends to decompensate very rapidly and this may quickly lead to death.30 |
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| Causation and fault |
To determine causation, Australian courts have had regard to what is
known as the but for test, where a plaintiff seeks to establish
that, without (or but for) a defendant's breach of duty, he or
she would have remained uninjured. It is recognised that applying
this test becomes difficult when there are a number of events which may
have influenced an outcome.31 There must also be an
application of common sense to the facts of each particular
case.32 Causation will be a very
difficult matter to determine in cerebral palsy cases because most
are caused by an antenatal condition which often may not have declared
itself before or immediately after birth. An absence of major risk
factors, such as intrauterine growth restriction, extreme
prematurity, twin gestation or known antenatal viral infections,
does not exclude congenital or acquired neurological deficit during
fetal development.
The Chief Justice of the Australian High Court, Justice Mason, has talked about important conceptual differences between causation in law and causation in science. . . . [In] science, the concept of causation has been developed in the context of explaining phenomena by reference to the relationship between conditions and occurrences. In law, on the other hand, problems of causation arise in the context of ascertaining or apportioning legal responsibility for a given occurrence . . . a person may be responsible for damage when his or her wrongful conduct is one of a number of conditions sufficient to produce that damage. [However,] . . . it is for the plaintiff to establish that his or her injuries are "caused or were materially contributed to" by the defendant's wrongful conduct. . . . Generally speaking, that causal connection is established if it appears that the plaintiff would have not sustained his or her injuries had the defendant not been negligent.33 Given our understanding of the rarity of preventable intrapartum causes of cerebral palsy and the difficulty of detecting antenatal causes before labour, it should not be necessary for a defendant to prove the likelihood of neurological abnormality of the fetus before labour or birth. The inability of a defendant to provide such details in retrospect should not allow the assumption that the origins of the cerebral palsy began in labour. It is for a plaintiff to prove the causative link between a putative breach and injury, not for a defendant to prove, in hindsight, the precise antenatal cause and timing of this condition. The standard of care required of health professionals is " . . . that to be expected by an ordinarily careful and competent practitioner of the class to which the practitioner belongs".34,35 Whether a medical professional has acted in accordance with a standard of reasonable care " . . . is a question for the Court [to decide] and the duty of deciding cannot be delegated to any profession or group in the community".36 Standards of care will be determined by the courts, not in isolation, but with regard to the evidence of expert witnesses who should give opinion based on scientific evidence. |
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| Expert witnesses |
Medical negligence litigation is mostly expert driven and a
plaintiff unable to procure good expert evidence to demonstrate
fault is unlikely to succeed.37 Equally, it is important
to have expert witnesses available to give evidence about the
standard of care to assist plaintiffs to present claims in the courts.
Problems arise when plaintiffs' advisers seek multiple verbal (and
untraceable) medical opinions, eventually selecting minority
views which may be expressed by those who lack recent or real expertise
in the particular area in question. Opinion on obstetric management
should be sought only from practising obstetricians endorsed by
their Colleges. Those giving care to the child in later life should not
make assumptions about causation. The inappropriate use of phrases
such as fetal distress or birth asphyxia should be
avoided.
This conference supports the concept canvassed in the 1994 interim report from the Review of Professional Indemnity Arrangements for Health Care Professionals:38 that the courts appoint acknowledged medical experts from lists chosen by the relevant Colleges. Medical evidence presented about best practice should rely on evidence-based medicine; for example, from randomised controlled trials which, in perinatal medicine, are easily accessible from the databases of the Cochrane Collaboration.39 The publication of these trials dates the information available at the time in question. Legal practitioners should be conversant with the medical issues involved before embarking on medical negligence litigation.37 |
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| Alternatives to litigation |
Studies suggest that patients initiate litigation partly to seek
compensation, but also to seek explanations and accountability and
to improve standards of care for other patients.40 The public may
have been given unrealistic expectations about pregnancy. Many may
be unaware that, based on current Australian data:
There is a great need to educate health professionals and the public that the origins of cerebral palsy are usually hidden and almost always occur during the pregnancy, only to become apparent after birth. Existing neurological problems may result in the fetus showing signs of distress during labour, but existing brain damage may not be prevented or reversed by earlier delivery or by caesarean section. The belief that cerebral palsy is often due to birth asphyxia is erroneous, and expectations that monitoring in labour might prevent many cases of cerebral palsy have not been met. Friends, relatives and caregivers may wish to offer simple explanations for complex problems and resolve typical grief reactions of anger, guilt and depression by attributing cerebral palsy to suboptimal care. In most cases there is no blame and there should be no guilt on the part of the parents or the caregivers. Early recourse to litigation tends to isolate the parents and child from those who could help and give explanations. Maternity staff are often unaware of the subsequent development of cerebral palsy and may not be asked to help in counselling. It is recommended that mechanisms should be available to encourage interviews between parents and the perinatal team that cared for the pregnancy and the baby with cerebral palsy. Independent expert advice should be offered when requested by parents. If the explanations are not satisfactory, or other issues are of concern, a hearing by a Complaints Tribunal38 may prove a quicker, cheaper and more satisfactory method of providing accountability and of checking standards, rather than resorting to prolonged and expensive litigation. Only when complaints are upheld by these tribunals should the details be made public and the necessity for further legal action be considered. |
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| Long term support services | All children with disabilities, and their parents, deserve appropriate long term support, including counselling, within the economic capabilities of the country. Parents of children with cerebral palsy should not have to risk expensive litigation to obtain financial help. As soon as possible, parents should have access to a comprehensive support service which includes paediatric rehabilitation, physiotherapy, occupational therapy and speech therapy. In Australia these services are provided to children with a disability at no cost to parents. Equipment is available through various government schemes such as Domiciliary Care. Respite for parents is also available through Home and Community Care and Community Support. In spite of the general availability of these services in most cities, there is a need for more services and more comprehensive services for all children with disabilities, without the need to prove causation or fault in their perinatal care. | |||||||||||
| Conclusions | There is no evidence that current obstetric practices can reduce the risk of cerebral palsy. The origins of many cases of cerebral palsy are likely to be antenatal. While obstetric interventions in the presence of signs of possible hypoxia may prevent fetal death, there is no evidence that they will limit the prevalence or severity of cerebral palsy. The antenatal signs of hypoxia and the methods to monitor hypoxia in labour are still imprecise. This can lead to overdiagnosis of severe hypoxia and, even when correctly diagnosed, early delivery by caesarean section may not change the risk of cerebral palsy. All expert witnesses and the public should recognise that the belief that caesarean section will prevent many cases of cerebral palsy is incorrect. There is a great need for further research into the antenatal origins and the prevention of cerebral palsy. This will include more cerebral palsy registries, improved methods of assessing the development and well-being of the fetus throughout pregnancy and labour, and better methods of assessing the neurological integrity of the baby before and after birth. | |||||||||||
| References |
* This statement follows a consensus conference held in Adelaide, South Australia, on 26 August 1994 and sponsored by the South Australian Health Commission. | |||||||||||
| Authors' details |
The Australian and New Zealand Perinatal Societies.
Alastair H MacLennan, MD, FRACOG, Associate Professor of Obstetrics and Gynaecology, University of Adelaide, Consensus Conference Chair.
No reprints will be available. Panel members: Fiona Stanley (Epidemiology), Institute for Child Health Research, Perth; Eve Blair (Epidemiology), Institute for Child Health Research, Perth; Greg Rice (Fetal Physiology), Royal Women's Hospital, Melbourne; Peter Stone (Obstetrics and Gynaecology), University of Otago; Jeffrey Robinson (Obstetrics and Gynaecology), University of Adelaide; David Henderson-Smart (Perinatal Medicine), University of Sydney; Victor Yu (Neonatal Intensive Care), Monash Medical Centre, Melbourne; Michael Harbord (Paediatric Neurology), Flinders Medical Centre, Adelaide; Leon Stern (Paediatric Rehabilitation), Crippled Children's Association of South Australia; Helen Chambers (Perinatal Pathology), Women's and Children's Hospital, Adelaide; Margaret Furness (Radiology), Women's and Children's Hospital, Adelaide; Tina Hayward (Radiology), Women's and Children's Hospital, Adelaide; Kerena Eckert (Midwifery Research), Women's and Children's Hospital, Adelaide; Christopher Boundy (Barrister and Solicitor), Adelaide; Susan Merrett (Medical Administration), South Australian Health Commission; Mark Kenny (Medicolegal Services), Women's and Children's Hospital, Adelaide. ©MJA 1998
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