Geographically based investigation of the influence of very preterm births on routine mortality statistics from the United Kingdom and Australia

david field ^1*, Barbara Bajuk ², Bradley N Manktelow ³, Trina Vincent ², Jon Stewart Dorling ⁴, William Tarnow-Mordi ⁵, Elizabeth S Draper ³ and David Henderson-Smart ⁶

¹ university of leicester, United Kingdom
² NSW Centre for Perinatal Health Services Research, NSW Pregnancy and Newborn Services Network, Unive, Australia
³ University of Leicester, United Kingdom
⁴ Nottingham University Hospitals, United Kingdom
⁵ Neonatology, Australia
⁶ University of Sydney, Australia

^* To whom correspondence should be addressed. E-mail: david.field{at}uhl-tr.nhs.uk.

Accepted 27 September 2007

Abstract

Background Comparisons of national perinatal and neonatal mortality rates often neglect the underlying causes. This study assessed effects of very preterm births in the UK and Australia. Setting Two geographically defined populations: the former Trent Health Region of the UK and New South Wales (NSW) / the Australian Capital Territory (ACT), Australia. Method All births 22+0 to 31+6 weeks born in 2000, 2001 and 2002 were identified by established surveys of perinatal care. Rates of birth and death were compared. Results The population of NSW/ACT was 35% higher and there were 66% more births than in Trent (273,495 vs 164,824). The proportion of liveborn infants between 22 and 31 weeks gestation was about 25% higher in Trent (NSW/ACT 2945, rate per 1000 livebirths 10.82 [95% C.I. 10.43-11.22]; Trent 2208, rate per 1000 livebirths 13.47 [95% C.I. 12.92-14.05]). The proportion of these infants admitted to a neonatal unit was also higher in Trent (91.2% vs 94.4%; OR 1.63; 95%CI 1.30-2.05). Unadjusted mortality in infants admitted to a neonatal unit was similar : NSW/ACT 332 / 2686 (12.4%), Trent 284 / 2085 (13.6%); unadjusted odds ratio = 1.12 (95% CI: 0.94-1.33) p = 0.21. Conclusion The higher rates of very premature birth and more ready admission to neonatal intensive care for those infants in the UK could help explain why its perinatal and neonatal mortality rates are higher than Australia's. Efforts to understand why the rate of premature birth in the UK is so high should be a national priority.

Keywords: infant mortality, perinatal mortality, prematurity

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