Re: Influence of definition based versus pragmatic birth registration on international comparisons of perinatal and infant mortality: population based retrospective study
We read with interest the paper by Joseph et al1 comparing perinatal indicators in Europe, the US, Canada and Australia/New Zealand. Joseph and colleagues conclude that variations in recording of births and deaths at very early gestational ages “compromise the validity of international rankings of perinatal and infant mortality.” Beyond the more general questions to be asked about the validity of ranking data in league tables at all,2 we believe that most countries have the capacity to report on their births and perinatal deaths in a way that make international comparisons valid and informative.
The European data presented in the study by Joseph et al. were compiled by the Euro-Peristat project with the aim of developing comparable indicators of perinatal health.3 It is important to clarify that our project collected and reported data on live births and fetal and neonatal deaths using a lower gestational age limit of 22 completed weeks,4 which reduced the variations due to registration differences in European neonatal and infant mortality rates. In fact, the data from Canada and the US are outliers and this makes them the primary drivers of the association between the proportions of live births with a birthweight under 500 grams and crude neonatal mortality rates that is reported in Figure 1. There is no association if the data are reanalysed without these two countries, as shown below. Further, for countries participating in the Euro-Peristat project there is a high degree of correspondence between overall neonatal mortality and mortality for births 1000 grams and over especially after excluding Malta and Luxembourg, whose rates fluctuate more widely because they have fewer than 10 000 births per year (Spearman's rank test, rho=0.85, p<0.001 n =21). This association does not indicate that differences in the recording of neonatal deaths do not exist between the countries of Europe5 or that these differences should be ignored, but that relative positions are robust.The situation is more complex for fetal mortality, since countries vary more in their recording procedures and policies towards screening and termination of pregnancies.5 6
Most countries have the capacity to produce gestational age and birthweight specific fetal and neonatal rates. These provide a much firmer basis for comparing these essential indicators and avoid the simplistic conclusions engendered by the league table approach. We showed that some countries experience excess mortality at term, whereas other have higher rates in the very preterm period,6 generating interesting hypotheses about the relationship between health care practices, the quality of health services and health outcomes. Stratified rates also make it possible to purposefully focus comparisons on the population of extremely preterm births. Large differences exist in the rates of very preterm birth in Europe, as well as in the care and outcomes for these babies.7 8 A population-based comparison of very preterm babies in ten European regions in 2003, for instance, found that survival to discharge after live birth at 24 to 27 weeks of gestation ranged from 43 to 81%.8
The WHO recommendations that international comparisons exclude births and deaths <1000 grams9 are no longer appropriate in this context. On the other hand, excluding live births with a gestational age less than 22 weeks is reasonable since survival below this limit is exceptional. Other exclusion criteria, such as a gestational age less than 24 weeks or birthweight less than 500 grams may ensure better comparability in some circumstances.
Given the burden of disease associated with stillbirth and neonatal death as well as the lifelong impairments resulting from very preterm birth, reliable indicators of perinatal health are badly needed. It is a matter of concern that Eurostat, the official statistical agency for the European Union, recently passed regulations making the provision of data on birthweight and gestational age voluntary for reporting of fetal and neonatal mortality rates.10 We agree with Joseph and colleagues that a common initiative bringing together national and international experts should develop updated guidelines for the international comparison of perinatal mortality statistics.
Jennifer Zeitlin, Béatrice Blondel, Ashna D. Mohangoo, Marina Cuttini, Alison Macfarlane, Mika Gissler, Sophie Alexander, Katarzyna Szamotulska on behalf of the Euro-Peristat Scientific Committee
1. Joseph KS, Liu S, Rouleau J, Lisonkova S, Hutcheon JA, Reg Sauve, et al. Influence of definition based versus pragmatic birth registration on international comparisons of perinatal and infant mortality: population based retrospective study. BMJ 2012;344:e746 doi: 10.1136/bmj.e746 (Published 17 February 2012).
2. Goldstein H, Spiegelhalter D. League tables and their limitations: Statistical issues in comparisons of institutional performance. Journal of the Royal Statistical Society, Series A 1996;159:385-444.
3. Zeitlin J, Wildman K, Breart G, Alexander S, Barros H, Blondel B, et al. PERISTAT: indicators for monitoring and evaluating perinatal health in Europe. Eur J Public Health 2003;13(3 Suppl):29-37.
4. EURO-PERISTAT project, wtih SCPE, EUROCAT, EURONEOSTAT. European Perinatal Health Report: available www.europeristat.com, 2008.
5. Gissler M, Mohangoo AD, Blondel B, Chalmers J, Macfarlane A, Gaizauskiene A, et al. Perinatal health monitoring in Europe: results from the EURO-PERISTAT project. Inform Health Soc Care 2010;35(2):64-79.
6. Mohangoo AD, Buitendijk SE, Szamotulska K, Chalmers J, Irgens LM, Bolumar F, et al. Gestational age patterns of fetal and neonatal mortality in europe: results from the Euro-Peristat project. PloS one 2011;6(11):e24727.
7. Field D, Draper ES, Fenton A, Papiernik E, Zeitlin J, Blondel B, et al. Rates of very preterm birth in Europe and neonatal mortality rates. Arch Dis Child Fetal Neonatal Ed 2009;94(4):F253-6.
8. Zeitlin J, Draper ES, Kollee L, Milligan D, Boerch K, Agostino R, et al. Differences in rates and short-term outcome of live births before 32 weeks of gestation in Europe in 2003: results from the MOSAIC cohort. Pediatrics 2008;121(4):e936-44.
9. World Health Organization. ICD-10: International Statistical Classificationof Diseases and Related Health Problems - Instruction Manual. 2. In: WHO, editor. Geneva: WHO, 2004.
10. Council of the European Union. 2010. Draft Commission Regulation (EU) No …/… of […] implementing Regulation (EC) No. 1338/2008 of the European Parliament and of the Council on community statistics on public health and health and safety at work, as regards statistics on causes of death. Available at: http://register.consilium.europa.eu/pdf/en/10/st17/st17002.en10.pdf, 2010.