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Introduction

The following article is based on datasets released by the Office for National Statistics (ONS). These datasets contain counts of infant mortality, that is to say, deaths under one year, together with infant mortality rates (calculated as the number of infant deaths per 1,000 live births). Infant deaths are allocated according to the mothers' usual place of residence and the data is provided for all regions and local authorities/districts in England and Wales. The total number of such infant deaths each year across England and Wales has been typically around the 3,300 mark over recent years but translated to local authorities and districts the annual case figures can often be small and can show large variations year-on-year. To resolve this and to ensure that the figures are sufficiently robust, ONS has published the data on infant mortality in the form of three-year rolling averages for the six-year period 1998/00 to 2003/05. The full dataset for the whole of England and Wales are available from the ONS Neighbourhood Statistics website. The relevant Lancashire statistics relating to these datasets can also be obtained from the Lancashire Profile Data Download Centre.

Background

Like birthweight (see Low Birthweight Live Births in Lancashire) the infant mortality rate, the proportion of children who die in the first year of life has traditionally been used as an indicator of the importance of both medical and non-medical determinates of health. The effectiveness of health systems is clearly an important factor but infant mortality is known to vary by a wide range of social and biological factors including mothers' age, birth multiplicity, ethnicity and/or country of birth, birthweight, socio-economic position, individual lifestyles and attitudes as well as area deprivation. Consequently these factors may all contribute to geographical variations.

All developed countries have seen considerable progress in reducing infant mortality rates from the level of 1970 when the average was approaching 30 deaths per 1,000 live births. The average today is less than 6 deaths per 1,000 live births, which equates to an overall reduction of over 75%. Around two-thirds of the deaths that occur during the first year of life are neonatal deaths (i.e. during the first four weeks). Congenital malformations, low birth weight of pre-term infants and other conditions arising during pregnancy are thought to be the principal factors contributing to neonatal mortality in developed countries. The large decrease in the rate of infant deaths over recent decades was dominated by the decline in neonatal mortality (in England and Wales for example, from 9.6 deaths per 1,000 live births in 1976 to 3.8 deaths per 1,000 live births in 2000). Mortality during the neonatal period is considered a goods indicator of both maternal and newborn health and care.

With an increasing number of women deferring childbearing and the rise in multiple births linked with fertility treatments, the number of pre-term births has tended to increase. These factors may have contributed to a levelling off or reversal of the downward trend in infant mortality rates in some countries over the past few years. For infant deaths beyond a month (post neonatal mortality), there tends to be a greater range of causes – the most common being birth defects, SIDS (sudden infant death syndrome), infections and accidents.

Lancashire Results

In simple numerical terms there were 306 infant deaths in the Lancashire sub-region over the latest three-year period 2003/05 (Table 1/Figure 1). This represented about 22% of the North West total or 3.1% of those in England and Wales. By district the largest number was recorded in Preston (45) followed closely by Blackburn with Darwen (42) whilst Fylde, Ribble Valley and Rossendale, each with eight infant mortality cases, had the lowest numbers.

Viewed over the full data period 1998/00 to 2003/05 the number of infant deaths in England and Wales fell by about 8%, though this conceals a small up-turn over the more recent years. The reduction and pattern in the Lancashire sub-region was of a similar order. There were, however, quite striking variations between local districts. On the positive side eight Lancashire districts recorded percentage rates of fall in infant deaths that were better than the national average. This reduction was particularly impressive in Chorley and Rossendale where the number of such deaths fell by a half. Such improvement was in sharp contrast with the position in Hyndburn, Pendle and Preston where infant mortality cases apparently increased by 30% or more over the period.

The number of infant deaths in a particular geographical area do not on their own facilitate useful comparisons over time or between areas due to differences in the size of the resident populations and in the total numbers of live births occurring in one area as compared with another. To enable such a comparison the number of infant deaths needs to be expressed as a ratio or rate – in this case the Infant Mortality Rate (IMR), the number of infant deaths per 1,000 live births. These rates are shown in Table 2.

Figure 1 Infant Mortality - Numbers and Rates, Lancashire, 2003/2005

Source ONS - Infant Mortality, 2003/2005

Over the latest three-year period 2003/05 the IMR in England and Wales stood at 5.2, down by about 9% compared with the 1998/00 period, though appears to have been fairly stable over more recent years. The equivalent rate for the Lancashire sub-region at 6.1% was significant higher though had shown an improving pattern over the full period similar to that of the nation. At the more local district level, a rather more mixed and in some instances a somewhat disturbing pattern is evident.

On the positive side six Lancashire districts had IMRs at or below the England and Wales average. Most notable in this respect were Chorley and Rossendale. Sharing a IMR of 3.4 both these districts ranked amongst the top 20% in England and Wales for low infant mortality – in marked contrast to the 1998/00 period when Chorley was amongst the poorest ranked 5% and Rossendale amongst the poorest 20% of all local authorities. The rankings of Fylde, South Ribble and Wyre were also in the top half of the national league table with the latter two districts steadily improving their position over that in 1998/00.

In contrast to these relatively favourable out-turns, eight Lancashire districts have IMRs above the England and Wales average. Indeed, in the most extreme instance an IMR of 9.9 in 2003/05 ranked Pendle as the poorest performing out of all 374 districts in England and Wales. The infant mortality statistics for local areas can be volatile year-to-year but the position of Pendle is further confirmed by the fact that it has occupied this bottom-ranked position in four out of the six three-year periods covered by the data between 1998-2005. Within a national context the Pendle IMR of 9.9 was more than eight times greater than highest-ranking East Hampshire with an IMR of just 1.2. Whilst being the most extreme instance, Pendle is not alone as two other Lancashire districts – Hyndburn and Preston are also ranked in the poorest 5% for infant mortality and Burnley was only just outside this range. Furthermore in each case and contrary to both the national and Lancashire pattern, the IMR of these four districts in 2003/05 were higher than they were in 1998/00 – in the case of Pendle and Preston about 30% higher. Other districts with IMRs above the national average – Blackburn with Darwen, Blackpool and Ribble Valley enjoyed some reduction in their rates and an improvement in their relative rankings over the full data period

Note on the Data

Statistics on infant mortality are drawn from routinely collected birth and death registration data which cover all births and deaths occurring in England and Wales. The datasets are based on infant deaths registered in the course of the calendar year from 1st January to 31 December inclusive. It should be noted that this differs slightly from data contained in the ONS 'Key Population Vital Statistics' publication since the latter is based on infant deaths occurring in a given calendar year (For example, a death occurring in one year may not be registered until the following year due to coroner's investigation). ONS also includes births to non-residents in its annual birth figures for England and Wales. The dataset used for the above analysis includes births to usual residents of England and Wales only.

The data is presented as three-year averages in order to smooth annual fluctuations in deaths and provide large enough numbers to ensure that the figures are sufficiently robust. However, upper and lower 95% confidence limits are also provided (contained in the Lancashire Profile download centre) so that, in comparisons between areas, those differences which are statistically significant (the confidence intervals of the two areas do not overlap) can be distinguished from those which could be the result of chance (the confidence intervals do overlap).

For further details, please contact:
Peter Kivell
Tel 01772 534157
Email Peter.Kivell@lancashire.gov.uk