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One-Year Mortality of Very Preterm Infants Admitted to Neonatal Units in England

Presented at the Neonatal Society 2015 Spring Meeting.

Ibrahim B, Statnikov Y, Gray D, Modi N, Saxena S and the Medicines for Neonates Investigator Group

Department of Primary Care and Public Health, Charing Cross campus; Section of Neonatal Medicine
Department of Medicine, Chelsea and Westminster Hospital campus, Imperial College London, SW10 9NH, UK

Background: Globally 130 million babies are born every year and nearly 4 million die in the first 28 postnatal days (1). Infants born very preterm constitute approximately one third of these deaths (2). The survival to discharge of preterm infants has been the focus of many studies however, there are few objective estimates of later survival. The purpose of this study was to describe mortality over the first year among very preterm infants by gestational age and differences in maternal characteristics by gestational age band.

Methods: We analysed data on infants, with a completed gestational age between 23+0 and 32+6 weeks, born in England between 1 January 2010 and 31 December 2010 and admitted to a neonatal unit (NNU). Data were extracted from a birth cohort created by linking the National Neonatal Research Database (NNRD) and the Hospital Episode Statistics (HES). We assessed differences in the frequency distributions of maternal characteristics by gestational weeks: maternal age (<20 years, 20-24 years, 25-29 years, 30-34 years and ≥35), ethnicity (White, Asian or Asian British, Black or Black British, Mixed and other Ethnic Groups) and social deprivation (defined using the Index of Multiple Deprivation quintile categories). We used chi-squared test to compare categorical variables by gestational age band. We determined mortality in the early neonatal (0-6 days), late neonatal (7-27 days) and post neonatal (28-365 days) periods by gestational age. This abstract presents independent research funded by the National Institute for Health Research (NIHR) under its Programme Grants for Applied Research Programme (RP-PG-0707-10010). The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health.

Results: We identified 7,463 live-born infants; 1.7% (n=129) were births at 23 weeks, 3.7% (n=273) at 24 weeks, 4.1 (n=307) at 25 weeks, 6.3% (n=468) at 26 weeks, 7.2% (n=535) at 27 weeks, 9.8 (n=733) at 28 weeks, 10.7% (n=801) at 29 weeks, 13.1% (n=977) at 30 weeks, 17.8 (n=1329) at 31 weeks and 25.6% (n=1911) at 32 weeks. There were significant differences in maternal age, ethnicity and social deprivation by gestational age. The frequency of mothers younger than 20 years of age, of black ethnicity and from the most deprived areas was higher in infants born at 23 weeks than those born at 32 weeks (23 weeks: 23.4%, 13.3% and 46.6%, respectively; 32 weeks:7.8%, 6.4% and 32.2%, respectively; p-values .0001, <.0001 and .009, respectively). Of all infants, 228 (3.1%) died during the early neonatal period, with mortality ranging from 35.7% at 23 weeks to 0.5% at 32 weeks, and 122 (1.7%) died during the late neonatal period, with mortality ranging from 18.1% at 23 weeks to 0.3% at 32 weeks. 178 infants (2.4%) died before in the post neonatal period and mortality ranged from 14.7% at 23 weeks to 0.7% at 32 weeks.

Conclusion: We found that among very preterm infants there were significant differences in maternal age, ethnicity and social deprivation. Early neonatal, late neonatal and post neonatal mortality was 3.1%, 1.7% and 2.4%, respectively. Our results for post neonatal mortality were similar to those reported by ONS for live-births in 2010 although we found higher mortality for infant born at 23 and 24 gestational weeks (14.7% and 11,7%; 7.6% and 9.9%). This may be explained by live born babies that die before admission to a NNU that are not therefore included in the NNRD, and to the fact that in the ONS reports there were high proportions of ‘Not Stated’ gestational ages concentrated in the North East Region. Our study reinforces the relevance of socio-economic circumstances in relation to preterm birth, and the importance of complete, accurate data recording.

Corresponding author: b.ibrahim@imperial.ac.uk

1. Zupan, J. Perinatal mortality in developing countries. N Engl J Med 2005; 352: 2047-8
2. Zeitlin, J 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: e936-44

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