Major new decision on Montgomery and causation in Birth Injury Cases

CNZ v. Royal Bath Hospitals NHS FT and SoS for Health and Social Care, 11 January 2023

  1. Mr Justice Ritchie has given judgment for the claimant in a historic CP case which has significant implications both for Montgomery and material contribution causation in clinical negligence cases, particularly those involving acute profound hypoxic ischaemia. The Claimant, a second twin, was born in 1996. She has profound disabilities as a result of about 16 minutes’ acute profound hypoxia.
  1. In summary:
  • Montgomery applied in 1996;
  • Montgomery applies to both antenatal consultations and decisions made intrapartum in the delivery room/ operating theatre;
  • Elective caesarean section was a ‘reasonable alternative treatment’ for twins in 1996 even where this was ‘not standard management’;
  • acute profound hypoxic ischaemia is a ‘divisible injury’ to which material contribution applies;
  • it is not possible to divide the functional outcome which would result from a shorter insult, so a claimant is entitled to damages in respect of 100% of her injury even if she would have suffered some injury in any event;
  • in an acute profound hypoxic ischaemia case, ‘every minute counts’.

Antenatal Montgomery

  1. The Claimant’s mother had a significant obstetric history and did not want either artificial rupture of membranes (ARM) or an epidural. She complained that she had been refused an elective caesarean section by a registrar in the antenatal clinic.  This allegation was defended on the basis that no such request had been made and that in 1996 the standard management for twins where there had been previous vaginal delivery, and where there were no concerns about fetal position, was vaginal delivery (NVD).  It was argued therefore that elective Caesarean section was not a ‘reasonable alternative treatment’.
  1. The Judge criticised the contradiction between saying both that elective caesarean (ECS) was not a reasonable treatment option and that if a mother had insisted she could have had one:

“There is an inherent illogicality in the approach taken by the Defendant’s department. All of the Defendant’s witnesses and Mr Tuffnell asserted that ECS was not a reasonable treatment option antenatally for M because she had achieved NVD twice before, was healthy and her twins were in a cephalic position and healthy. But they all also gave evidence that if M had requested CS and persisted, despite being put through two or perhaps three counselling sessions against that choice, they would and should have agreed to her choice for ECS as her birth plan.”

  1. On this basis the Judge found that elective caesarean section was a reasonable alternative treatment in 1996. This part of the claim failed though because he found that on the facts there had actually been a discussion which included the option of ECS and the mother had gone on to agree to induction.
  1. Nevertheless his decision has significant implications for other cases where, perhaps in line with standard management at the time, a particular treatment was not offered but where a patient could have had it had they insisted or fought hard enough.

‘Delivery room’ Montgomery

  1. Before now the courts have been cautious about applying Montgomery in the context of an imminent delivery rather than antenatally. See ML v Guy’s and Tasmin v Barts. This has always troubled me because I don’t see in principle why personal autonomy should be reduced by pain, stress or other factors attributed to mothers who are about to give birth.
  1. In this context CNZ is a major step forward because Ritchie J held that a maternal request for caesarean section in the period between the first and second twin should have been heeded.
  1. After the birth of the first twin at 0001 the Claimant was not delivered until 0103. A second twin normally descends into the pelvis but in this case the Claimant remained ‘high’. This left the junior obstetrician with a choice of caesarean section or ‘high ARM’ – rupturing the membranes and hoping that the baby’s position did not change in a woman with no epidural.  Both options required transfer to theatre.  The court held that the registrar took matters too slowly and that the Claimant should have been delivered some 5 to 8 minutes earlier The Judge took the midpoint figure of 6 ½ minutes as the period of culpable delay.  This was a straightforward Bolam decision.
  1. Ritchie J. went on however to accept two significant breaches of Montgomery in the 40 minutes prior to CNZ’s delivery. Firstly, when the registrar left the delivery room to phone the on-call consultant to check her management plan of ‘high ARM’ in theatre she failed to discuss the options first with the parents. Had she done so then she would have understood that they were implacably opposed to any other option than caesarean section and would have relayed this important fact to her consultant.

“I consider that Mr Forbes’ criticisms of Doctor Tristram at this point are reasonable and valid.  I consider that what the Doctor ought to have done is to set out the options, the risks and benefits and to seek the parents’ choices on those options before going to the consultant.   In my judgment Montgomery applied at this point. Doctor Tristram needed to know, before she checked with the consultant, what the parents’ choices were. To obtain their informed choices she needed to inform them of the risks and benefits of the options of CS or NVD with possible ARM (low and high).  She should have given them the right to choose CS and asked whether they would accept low or high ARM or ARM at all.”

  1. The second Montgomery breach occurred when the registrar returned from speaking to her boss. She told the parents that the plan was for ARM in theatre but they point blank refused, insisting on a caesarean.  Instead of agreeing, which she should have done, Dr Tristram told them that they would go to theatre and the position could be re-assessed there.  In theatre the mother again refused an ARM at which point instead of proceeding to caesarean the doctor telephoned the consultant for a second time before finally agreeing to the section. The Judge found:

“I accept the Claimant’s criticism of this approach as too paternalistic. Patient choice was being ignored at this stage. Doctor Tristram was, on her own evidence, proceeding with ARM having not obtained permission to do a high one so and she did not record M’s permission to do so.  The parents were requesting CS and in my judgment at that time in the circumstances Doctor Tristram should have agreed to that request.”

How far back does Montgomery apply?

  1. The Judge queried how retrospective Montgomery actually is. Noting that this decision was based on acknowledgment of changing attitudes to consent which reflected greater personal autonomy and access to information, especially from the internet, he accepted that it did apply in 1996, which was 3 years before Nadine Montgomery delivered, but questioned whether it applies much earlier than about 1993:

“[Montgomery] applied to the 1999 events in the case, but how far back can this decision be taken? I doubt it can be taken as far back as the 1950s or 1960s.  I make no decision on those decades.  I wonder if it could be applied to clinical practice in the 1980s.  Again I make no decision on that question.  As for the 1990s, taking into account the rationale expressed for the movement from paternalism to patient choice there may be a tipping point at which the growth of the internet (Berners-Lee released his system in 1993), the changes in societal values and the passing of the Human Rights Act 1998 and other legislation came together to generate the change from paternalism to patient choice.  So does Montgomery apply to the facts of this case in February 1996 two years before the passing of the Human Rights Act 1998 and before the internet had really developed much?  I admit that I am troubled by this. I consider that it probably does.  I have considered whether a watered down form of the ruling would have applied or whether a tapered growth of the Montgomery duty to consent properly could be the correct approach in 1996 but I do not consider I am permitted to do so as a Court of first instance without an indication for such in the Supreme Court’s judgment.”

  1. I am not aware of any decided Montgomery cases where the treatment pre-dates 1996 and we will have to wait to see how this issue develops.


  1. There were four major issues on causation:
    1. First, does every minute count in acute profound hypoxia?
    2. Second, is acute profound hypoxic ischaemia a divisible injury?
    3. Third, where the Defendant has not caused all of the injury should there be a reduction in damages to reflect this?
    4. Fourth, can damage from acute profound hypoxia be divided into 5 minute aliquots?

Every minute counts

  1. As far as I am aware, this case is the first time that the court has acknowledged that in the context of acute profound hypoxic ischaemia every minute really does count. This will be of great significance in many other cases where a breach of duty is agreed or found to have led to only a couple of minutes delay in delivery.
  1. The starting point is the agreed and conventional understanding that in acute profound hypoxia the first 10 minutes of an insult is generally non-damaging. It is further understood that after about 25 minutes a baby is unlikely to survive.
  1. Ritchie J accepted that every minute of acute ischaemia after the first 10 minutes causes more than minimal damage even though it was not possible to quantify the difference in function which this causes:

“The agreed evidence was that every minute of acute PHI over the first 10 minutes caused increasing or incremental brain cell deaths which could number in the tens or hundreds of thousands.  I find that this damage minute by minute was more than de minimis. In addition each minute caused increased functional outcome disability and injury.

“I find that on the evidence before me, that medical science is unable to identify with accuracy or detail the functional effect of each minute of brain cell deaths. Both experts, Doctor Newton and Doctor Rosenbloom advised that they could not accurately predict the pattern or severity of the resulting functional disability from a minute by minute increase in the duration of the PHI suffered.”

Divisible injury

  1. Much confusion has arisen from different judges using the term ‘indivisible injury’ in different contexts. So for example a defendant might point to the Court of Appeal in AB v. Ministry of Defence, or Soole J in Thorley and argue that ‘material contribution does not apply to cases of indivisible injury’.
  1. Without rehearsing here the competing arguments I recommend all practitioners read Ritchie J’s analysis where he sets out in detail Lord Phillips’ categorisation in Sienkiewicz.
  1. Lord Phillips had made a distinction between ‘trigger’ injuries (whether malaria from a single mosquito bite or after a sufficient cumulative dose of a noxious substance) and those that are ‘dose related’ and therefore ‘divisible’.
  1. On this basis Ritchie J explains that acute profound hypoxic ischaemia, which is dose related, is properly described as a ‘divisible’ injury, but crucially for practitioners struggling with the terminology, it is an injury to which material contribution applies and where the term ‘indivisible’ may be applied to the functional outcome. He held:

“I do not consider that the term indivisible applies to the Claimant’s brain injuries in this case. An indivisible disease is one which starts when triggered and then goes on and gets worse or takes its course whatever the exposure to the noxious substance after the triggering event.  These diseases are not divisible in the sense that they are not reduced by stopping the exposure and do not get worse on increasing the exposure.  They start and then they progress, like cancer or mesothelioma. 

Brain damage caused by PHI [profound hypoxic ischaemia] is not a trigger disease.  It does not grow like cancer or mesothelioma once triggered.  The spread of brain damage due to PHI is wholly dose dependent.  The more PHI the fetus suffers the greater the brain damage.   However the word indivisible may apply to the functional outcome caused by one or more minutes of acute PHI.“

  1. Ritchie J therefore concludes:

“In my judgment the relevant test in brain injury caused by acute PHI is firstly the but for test and then in relation to the functional outcome the material contribution to the injury (not to the risk of injury) approach.”

  1. By ‘but for’ he means this: ‘but for the breach of duty would there have been damage?’

Should there be a discount?

  1. In CNZ the Judge found that the probable length of the insult was 16 minutes. CNZ had been delivered at 0103 and the insult continued until restoration of the fetal circulation at 0106. The insult therefore probably started at 0050.  Had the 6 ½ minutes of negligent delay been avoided she would have been delivered at around 0056/ 0057.  This would have meant an insult of less than 10 minutes and she would probably have been uninjured. Therefore on his factual findings all of the injury was caused by the negligence on a conventional ‘but for’ analysis.
  1. Ritchie J was troubled however by the question of what to do in circumstances where earlier delivery would have avoided some but not all of the damage.
  1. We saw above that he did not regard acute profound hypoxic ischaemia as an indivisible injury.
  1. But he acknowledged that this leaves the different issue of whether you can divide the functional outcome. Can you say what level of injury would probably have been suffered in any event? At this point Ritchie J reviewed the full range of causation authorities from the personal injury canon (Holtby, Allen, Thompson). This led him (correctly) to the conclusion that if possible there should be an apportionment:

“In my judgment these authorities would support a ruling in the present case that a fair way to apportion the damages in a brain damage case caused by acute PHI at birth would be by way of a percentage based on the relative durations of the PHI caused by the breach compared to the PHI which would have been suffered in any event.   This is so even though none of the parties and none of the medical experts supported the percentage apportionment approach in this case.  I consider apportionment in law to be a judicial decision arising from the evidence not the medical decision of an expert.”

  1. In practice however he accepted that in an acute profound case such an apportionment was likely to be impossible. Importantly for claimants in other cases he accepted the approach of Picken J. in John v Manchester.

“I accept that there is a distinction to be drawn between impossibility of proof of apportionment of functional outcome and difficulty over proof of apportionment of functional outcome. I consider that in that case before me, where the Claimant’s cerebral palsy has been caused by one noxious factor: acute PHI, and where the agreed medical evidence is that every minute of PHI caused increasing brain damage, the only scientific gap is how to attribute each minute of brain damage to each or any functional deficit.”

  1. This meant that if the length of the insult was such that, contrary to his primary finding, CNZ would have suffered some injury in any event she would nevertheless be entitled to damages in respect of the whole of her injury:

“In law I consider that the cases I have reviewed above show that if there is a scientific gap making proof of causation of functional outcome, therefore also quantification, impossible in contra-distinction to merely difficult, then the Claimant will recover 100% of the damage she has suffered due to the PHI so long as the Claimant can prove that the breach made a material contribution to the functional outcome.”


  1. For many years Lewis Rosenbloom, perhaps the most experienced expert neurologist in the world of cerebral palsy litigation, has been floating the idea that it might be possible for the court to adopt a ‘best fit’ approach to cases of acute profound hypoxic ischaemia. His attempt has been to identify a level of ‘but for’ injury in a case where there would have been some injury in any event.   Applied to CNZ’s case he argued that if we start from the assumption of a 20 minute injury then saving a few minutes of hypoxia would not make a difference to the outcome because the claimant would still have been within the ‘15-20’ minute cohort.  The characteristics of this cohort are set out in appendix 1 to the judgment but include GMFCS IV, severe dysarthria, some cognitive impairment, leaving the claimant neither socially nor economically independent.
  1. Dr Rosenbloom went on to argue that if the court were to find that delivery should have been about 5-7 minutes earlier then the Claimant would have been in the 10-15 minute cohort so her damages should be discounted to reflect the level of disability that she would probably have had in any event i.e. preserved cognition, GMFCS II, some reduction in economic capacity.
  1. Dr Newton, for the Claimant, strongly disputed the Rosenbloom approach. Dr Newton argued that every person with cerebral palsy is a unique individual and you cannot just lump people together without considering their individual characteristics.  This is borne out by the reality that in every quantum case we have up to 10 experts reporting on the particular features of that individual.
  1. Ritchie J. rejected the aliquot argument, in part because there just was not enough evidence (for example a database like that used for the calculation of life expectancy by Strauss et al) to permit the distinctions suggested.

“So in my judgment the Aliquot theory, honestly and helpfully put forwards, as it was, by an impressive, helpful and experienced expert, is not an acceptable, fair or practicable way to apportion quantum in Cerebral Palsy cases caused by PHI.”


  1. This was an important case, heard by a very experienced clinical negligence judge, with impressive experts (including Forbes, Tuffnell, Dear, Fox, Newton and Rosenbloom). Ritchie J. has grappled with some of the most significant issues facing cerebral palsy lawyers and given clear answers.  This case is a major advance.




11 JANUARY 2023


[1] John was instructed for the Claimant by Susan Brown of Boyes Turner