Minimum case numbers for preterm infants: indications of a relationship between provider volume and mortality

There are indications that in the medical care of preterm infants and neonates with a birth weight lower than 1500 gram, mortality decreases with an increase in the number of cases (volume) treated in a hospital. However, it cannot be inferred from the available study data that a higher provider volume is the reason for a lower mortality rate. As sufficient data on complications related to preterm birth are also lacking, no conclusions on the relevance of case numbers for the overall quality of outcomes are possible. This is the result of the final report published by the German Institute for Quality and Efficiency in Health Care (IQWiG) on 14 October 2008.

German Federal Joint Committee considers extended requirements for perinatal centres

In order to reduce mortality and minimize early childhood disabilities, the Federal Joint Committee restructured the requirements for the medical care of preterm infants at the beginning of 2006. Since then, infants with an expected birth weight of less than 1500 gram have to be cared for in special centres, which need to fulfil specific requirements, for example, concerning technical, constructional, and staff resources.

Subsequently, the fees per case for preterm infants were adjusted accordingly and created a financial incentive for more and more hospitals to establish perinatal centres. Experts fear that this may not only result in a reduction in the number of preterm infants per centre, but also in the rate of successfully treated children.

In order to counter such a development, the Federal Joint Committee is considering extending the requirements for perinatal centres by requesting a minimum provider volume for treated preterm infants. In July 2007, the Committee therefore commissioned IQWiG to assess whether there was a relationship between the number of treated cases and the quality of outcomes in preterm infants with very low birth weight, on the basis of the available scientific evidence.

No intervention studies available

The IQWiG researchers identified a total of 10 studies that could be included in the assessment. All studies were observational. No intervention studies comparing hospitals with and without minimum volumes are currently available.

Eight of these studies investigated mortality as the primary outcome. Only 4 studies investigated the relationship between provider volume and morbidity, i.e. medical complications related to preterm birth.

Studies do not show a completely uniform picture

Not all studies showed a statistical relationship between provider volume and mortality rates. However, overall the data provided clear indications that a greater number of cases was associated with better chances of survival. This was particularly shown in studies with German health care data.

However, one cannot automatically conclude from such a statistical relationship that a higher provider volume is the reason for a lower mortality rate. Such a causal relationship can only be proven with intervention studies in which hospitals in regions with and without regulations on minimum volumes are directly compared with each other. As such studies are lacking so far, it is unclear whether an increase in case numbers would lead to a better quality of outcomes.

Moreover, the picture remains incomplete if one only assesses mortality rates. Without doubt, mortality is of key relevance. However, clear data are also required on complications related to preterm birth, such as brain haemorrhages or lung disease. As the corresponding data are scant and unclear, a conclusive evaluation is not possible.

Introduction of minimum provider volumes only with accompanying evaluations

As none of the studies were designed to determine threshold values for minimum provider volumes, the final report does not draw conclusions concerning the number of cases above which no further increase in the quality of outcomes occurs. There is therefore no sound scientific basis for specific threshold values.
If minimum provider volumes are to be introduced, the Institute recommends an accompanying evaluation, which should be designed in such a manner that it can be determined whether this intervention actually leads to an improvement in the quality of outcomes in preterm infants.

Procedure of report production

At the request of the contracting agency, the Federal Joint Committee, the commission was given preferential consideration by IQWiG. The preliminary report plan was published in mid-September 2007, barely 2 months after the award of the commission. The preliminary report followed in May 2008. A hearing was performed after the publication of both documents.

The written comments on the preliminary report and the meeting minutes of the oral debate have been published in a separate document simultaneously with the final report. In particular, the discussion section of the report (pp. 48-58) addresses the arguments presented in the written comments in detail.

The executive summary provides an overview of the background, methods, and additional results of the final report.

Contact: Tel. ++49(0)221-35685-0, info@iqwig.de