Improving odds for preterm babies

Preterm infants admitted to high-volume neonatal units are far less likely to die compared to those admitted to low-volume units, new research shows.

The study, published by the online medical journal BMJ Open, provides new insights about how organisational factors in England affect the prospects for infants born before 37 weeks of gestation.

In comparing the high- and low-volume units, the analysis uncovered striking differences for preterm babies, and particularly for those babies born at less than 27 weeks of gestation - findings that are certain to play a part in the ongoing debate over how to organise medical services to provide the best care for these vulnerable infants.

Results demonstrated that for preterm babies born at less than 33 weeks of gestation, the odds of dying in hospital were 32 per cent less if they were admitted to high- volume units at the hospital of birth than if they were admitted to low-volume units. For babies born at less than 27 weeks, the effect was greater, with the odds of dying almost halved when they were admitted to high-volume neonatal units at the hospital of birth compared to when they were admitted to low-volume units. (The analysis does not include those preterm babies who died on obstetric wards before being admitted to neonatal units.)

Policymakers need to think about the best organisation of medical care for preterm infants.

‘One possible explanation for our results could be that those neonatal units delivering a greater volume of care provide the clinicians who work there with more experience,’ said first author Sam Watson, a University of Warwick PhD student based in the Department of Economics and the Medical School. ‘The first hours of these babies’ lives can be crucial, which means it is essential to give them expert care at this time. It is also possible that economies of scale play a role, in that the larger and busier units have more resources to invest in technology and facilities. However more research is needed to tease out the possible explanations and inform policy effectively.’

The study, by a team of eight medical, statistical and economics researchers, was carried out on behalf of the Neonatal Economic, Staffing and Clinical Outcomes Project (NESCOP), a collaboration between researchers based at the University of Warwick, University College London, Imperial College London, Leicester University and at Bliss, a UK charity that focuses on babies who are born prematurely or otherwise require special care.

‘This research underscores the importance of academic collaboration to bring together expertise from different fields of study,’ said Wiji Arulampalam, a professor in the Department of Economics at the University of Warwick, who is a co-author of the study. ‘The study was made possible by combining medical expertise and statistical techniques used by economists. A standard statistical analysis would not have been able to identify the causal effect of the neonatal units’ characteristics on the health outcomes for preterm babies.’

The results of the study emerge at a time of considerable debate about the organisation of critical care services for newborns, especially in relation to the volume and intensity of care units. In 2003 the UK created a model of networked, regionalised units to facilitate the transfer of preterm babies to higher care specialist units, whilst also maintaining access to less specialist low volume units for those mothers and babies less at risk. These are now known as English Operational Delivery Networks. The results of this study support this approach, but the researchers call for a need to further evaluate the effect of the transfers and to consider ways to improve procedures surrounding them.

The differences in the outcomes for very preterm infants were especially striking.

‘This study has generated policy-relevant evidence that, hopefully, will lead to patient benefits,’ said Stavros Petrou, a health economics professor at the University of Warwick Medical School, and a co-author of the research.

The authors concluded, ‘The effect of volume on neonatal outcomes is an important consideration for policymakers deciding on the optimal organisation of neonatal specialist services.’

Using data from 165 of the 174 neonatal units in England for a three-year period from 2009 to 2011, the researchers analysed a range of clinical outcomes for preterm babies admitted to high volume neonatal units and compared them to outcomes for preterm babies admitted to those units not classified as high volume. For this study, high-volume neonatal units were defined as those that provide more than 3,480 care days to preterm babies per year. Several possible factors that could influence the statistical analysis were taken into account including age, birth weight and sex of the baby.

Data were analysed for 20,554 babies born at less than 33 weeks and for 2,559 babies born at less than 27 weeks. Twenty-four per cent of the neonatal units were classified as high volume and 46.4 per cent of infants born at less than 33 weeks were born in hospitals with a high-volume neonatal unit. The majority (78 per cent) of high-volume units were also specialised Neonatal Intensive Care Units (NICUs).

For babies born at less than 27 weeks of gestation, the odds of dying almost halved in high-volume units, compared to low-volume units.

Researchers showed that, although the odds of dying in hospital were 15 per cent lower if babies were admitted to specialist units compared to non-specialist units, this was not a statistically significant reduction. This indicates that although many high-volume units are also specialist NICUs, it is the amount of care rather than the designation of the unit that seems to be the key determining factor.

‘It is already established best practice to transfer women who are at risk of preterm birth prior to delivery,’ said Neena Modi, a professor in the Department of Medicine at Imperial College London, and a co-author of the study. ‘This is known to be safer than transferring vulnerable babies after birth. Currently there are a large number of requests for this type of transfer, but sadly very many do not take place because of organisational barriers and lack of cots. Our study suggests that, given the benefit of giving birth in a hospital with a high-volume neonatal unit, there should be a greater push to improve the situation and review current procedures in a systemic fashion.’

Sam Watson also cautioned that the policies need to be evaluated carefully. ‘Our study indicates that ensuring very preterm babies, particularly those born at less than 27 weeks, are delivered in hospitals with high-volume neonatal units improves their outcome, but there could be a knock-on effect on other patient groups if smaller neonatal units are closed,’ he said. ‘Babies who are not born so early but who are still vulnerable may have to travel far from home as a consequence, and this is why further research is urgently needed.’

The academic paper, ‘The Effects of Designation and Volume of Neonatal Care on Mortality and Morbidity Outcomes of Very Preterm Infants in England: Retrospective Population-based Cohort Study,’ is available here.

The co-authors are University of Warwick researchers Sam Watson, Wiji Arulampalam, Stavros Petrou and the following researchers elsewhere:

• Neil Marlow, professor of neonatal medicine, and Andrei Morgan, senior clinical research associate; both in the Academic Neonatology Department at the University College London Institute for Women’s Health
• Elizabeth Draper, professor of perinatal and paediatric epidemiology in the Department of Health Sciences at the University of Leicester
• Shalini Santhakumaran, statistician, and Neena Modi, professor of neonatal medicine; both in the Section of Neonatal Medicine in the Department of Medicine at the Chelsea and Westminster Campus of Imperial College London.

Bliss provides funding for the NESCOP group. Sam Watson receives funding from both Bliss and the Department of Economics at the University of Warwick.