Where Every Minute Counts: Hypoxic Birth Injuries – Causation and Material Contribution

Please note, an edited version of this article was first published in PI Focus July 2025 edition.
 

Legal claims for hypoxic brain injuries during birth – caused by a disruption in oxygen supply - remain prevalent. These injuries can have a devastating impact and lead to lifelong conditions including Cerebral Palsy. Indeed, claims relating to brain injuries sustained during birth account for a significant percentage of the total value of clinical negligence damages paid out each year. This is because the average amount of damages for such cases is very high, not infrequently running to tens of millions of pounds, with some impacted children having lifelong needs for care, treatment, equipment and housing. Nonetheless, claims for clinical negligence in this area can be particularly thorny to prove. In this article I consider when the doctrine of ‘material contribution’ – said by the Court of Appeal to have been ‘bedevilled by apparent inconsistency’ – may apply to hypoxic birth injury cases where the window for avoiding injury can be short. Does every minute really count?
 

In these types of claims, commonly the allegations of breach of duty centre around a need to deliver the baby sooner, such as via caesarean section. Causation – generally what difference earlier delivery would have made – can be especially complicated.

It is vital that alternative causes for the brain injury, aside from the negligence / delayed delivery, are considered. For example, these could be that a baby has an underlying brain abnormality, or that a haemorrhage took place while the baby was in the uterus and before delivery should arguably have happened in any event.

With a negligently delayed delivery, the period of delay is key. The opportunity for avoiding brain damage once oxygen / blood flow is compromised can be a matter of minutes. It is generally considered that acute profound hypoxia starts to cause brain damage after 10 minutes. After around 25 minutes it is considered unlikely that a baby will survive.

Where there is a period of acute hypoxia caused by negligence but also a period of ‘non-negligent’ hypoxia, or indeed where there are otherwise both negligent and non-negligent cumulative causes, proving causation on a standard ‘but for’ basis may not be possible. (The standard basis would be that ‘but for’ the negligent delay the brain injury would have been avoided altogether.) However, the doctrine of ‘material contribution’ can be particularly germane in such hypoxic birth injury claims. It may enable the Claimant to be compensated in full for the injuries suffered where ‘but for’ causation cannot be proven but where it is nonetheless possible to show that the negligent period of delay made a material contribution to the injury along with other ‘non-negligent’ factors.

What cannot be underestimated is that material contribution is a highly complex area. The concept, of course, arose in industrial disease cases, perhaps most notably Bonnington v Wardlaw [1956], and the key issue has often been seen as whether an injury is ‘divisible’ or ‘indivisible’. The doctrine has been considered in a great many other cases which I will not seek to rehearse here, but I must note the 2023 case of Holmes v Poeton Holdings Limited [EWCA Civ 1377] (a clinical negligence case relating to toxic substances and Parkinson’s Disease). In that case the Court of Appeal provided a definition of indivisible and divisible injuries - divisible diseases are those where ‘their severity will be influenced by the total amount of the agent that has caused the disease’. However, with an indivisible disease once contracted ‘its severity will not be influenced by the total amount of the agent that caused it’.

The Holmes case is an important one which, after decades of uncertainty, seems to have confirmed that material contribution applies to both indivisible and divisible injuries, although the later are to be approached differently (see paragraph 60 of the Judgment). Despite this, on the facts of the case in Holmes a material contribution to the injury was not made out… the case makes clear that the evidential bar for proving material contribution is not a low one. The Judgment is essential reading for those interested in this area.

The Holmes Judgment suggests that in cases of divisible injuries a Claimant should recover that part of their loss caused by the negligence. Where the injury is indivisible and a material contribution can be shown, the Claimant could recover in full.

Looking at the doctrine in the case of hypoxic birth injuries specifically, the case of CNZ v Royal Bath Hospitals NHS Foundation Trust [2023] - a High Court case shortly before Holmes – set out very helpful analysis and acknowledged that, in terms of acute profound hypoxic ischemia (PHI), every minute does in fact count.

This case related to the birth of a second twin in 1996 who was diagnosed with significant disabilities due to acute profound hypoxia. It was found that there was a delay in delivery of the twin with a likely total duration of acute PHI of 16 minutes - 6.5 minutes of which were negligent / avoidable. The breaches related to informed consent and caesarean section. As to causation, the Judge in the case, Ritchie J, found that on a standard ‘but for’ basis the Claimant succeeded. It would appear that the negligent delay accounted for the whole injury given that the first 10 minutes would be non-damaging.

However, Ritchie J went beyond this in his analysis to look at the issue of material contribution and what to do where earlier delivery would have prevented some but not all of the damage. He found, based on the expert evidence in the case, that every minute of acute PHI beyond the first 10 minutes ‘caused increasing or incremental brain cell deaths’ and that, minute by minute, this damage was more than ‘de minimis’. He went on to say: ‘In addition each minute caused increased functional outcome disability and injury.’

Ritchie J went on to find that medical science is unable to identify with accuracy or detail the functional effect of each minute of brain cell deaths. The paediatric neurologist for the first Defendant, Dr Rosenbloom, a renowned expert in this area, gave evidence that it was possible to advise on the functional outcome, but only by using five-minute aliquots. Ritchie J, while acknowledging that the theory was put forward honestly and helpfully by an experienced expert, considered that it was not a ‘fair or practicable way to apportion quantum in this Cerebral Palsy case caused by PHI.’

Ritchie J drew a distinction in the CNZ Judgment between ‘trigger’ injuries and ‘dose related’ injuries. He stated that brain damage caused by acute profound hypoxia is dose related and as such is a divisible injury. Ritchie J noted that brain injury caused by PHI 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.’ Ritchie J confirmed that this is an injury to which material contribution applies. He explains that ‘the word indivisible may apply to the functional outcome caused by one or more minutes of acute PHI.’

Ritchie J concluded that the relevant test for 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) approach.’

Ritchie J stated that in his view a fair way to apportion the damages would be by way of percentages based on the relative durations of the PHI caused by the negligence, compared to the PHI which would have been suffered in any event. However, having considered various cases he stated that none of them resolved the issue of apportionment, in cases of brain damage caused by acute PHI at birth, where the functional outcome cannot be apportioned or divided. He noted that in CNZ ‘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 scientific gap is how to attribute the breach PHI (or each minute of brain damage) to each or any functional deficit.’

He concluded that if there is a scientific gap such that it is impossible to prove the causation of functional outcome, and therefore also to quantify it, the Claimant will recover in full for the damage suffered so long as they can prove ‘that the breach made a material contribution to the reduced functional outcome which was more than de minimis’. Ritchie J emphasised that ‘impossible’ is distinct from ‘merely difficult’.

This was, of course, an alternative finding to Ritchie J’s primary position that causation in this case was made out on a standard ‘but for’ basis. Ritchie J gave permission for an appeal on his approach to material contribution although no appeal Judgment has been published to date.

What if the negligent delay was just one minute?
 

It is interesting to consider all of the above in the context of the 2023 Court of Appeal case of CDE v Surrey and Sussex Healthcare NHS Trust, which shows how tight the window of opportunity for material contribution can be. In this case the Claimant suffered quadriplegic Cerebral Palsy due to PHI following an alleged delay in delivery.  The Claimant’s case was that, but for a negligent delay in sending the Claimant’s mother to the labour ward, the emergency caesarean section - that took place once an obstetrician identified bradycardia (a slow heartbeat) - would have been performed sooner and the Cerebral Palsy would have been less severe.

The Judge was again Ritchie J, who made detailed findings of fact on timings and found breaches of duty, but dismissed the claim on the basis that the PHI would have occurred in any event. The Claimant appealed to the Court of Appeal, which found that the obstetrician would, absent the negligence, have been present one minute earlier. Experts in the case had not specifically considered what difference the baby being delivered a minute earlier would have made. The Court of Appeal concluded that the issue should be remitted back to Ritchie J to consider, having heard further expert evidence. This case provides a good example of where hypoxic birth injury claims may not, in fact, fully crystallise as to causation until a long way through the legal process and, potentially, not until the Judge has made findings of fact in respect of breaches of duty.  To date, no further Judgment has been published in the CDE case.

However, on the reasoning from CNZ v Royal Bath Hospitals, where Ritchie J found that minute by minute damage was more than ‘de minimis’, there appears to be potential for a finding of material contribution on the basis of only a one-minute delay. However, would the length of overall PHI impact the approach? In CDE the Claimant suffered a significant period of PHI - around 23 – 24 minutes according to Ritchie J.

Going forward, the Judgment in Holmes will need to be considered when dealing with material contribution in hypoxic brain injury cases. Interestingly, the possibility of apportionment in indivisible injury cases was left open. However, does the Judgment support Ritchie J’s analysis in CNZ v Royal Bath Hospitals that material contribution can apply and the Claimant recover in full where the impact on functional outcome is indivisible but the injury process itself is divisible?

I would suggest that Ritchie J’s reasoning is practical and user friendly for birth injury claims and that as matters stand, practitioners need to be looking at whether there is indivisibility of functional outcome in such cases.

In any event, both CNZ and CDE are authorities showing that every minute in PHI cases is relevant and reinforce the need for a careful and forensic analysis of timings when managing such claims. It is crucial for clinical negligence practitioners to create realistic and robust counter factual timelines to allege what should have happened during the birth and when. Further judicial guidance seems likely, particularly as to apportionment of damages.

About the author

James is the Head of our Medical Negligence and Personal Injury practice and joined the firm in 2023 from Hodge, Jones & Allen. He has undertaken medical negligence and personal injury cases for over 30 years.