Low Birthweight Live Births in Lancashire

Introduction

The following article is based on datasets released by the Office for National Statistics (ONS) via their Neighbourhood Statistics website. These datasets contain counts of low birthweight live births occurring in each of the calendar years 1999 to 2004 in England and Wales to mothers usually resident in England and Wales. Information is provided for regions and local authorities/districts. Allocation to geographical area is based on mother's place of usual residence and not on the place where the births occurred although in the case of home births these may be the same. The relevant Lancashire statistics relating to these datasets can be obtained from the Data Download Centre.

Background

Low birthweight babies are defined by the World Health Organisation as those that weigh less than 2,500 grams at birth. Below this value birthweight specific infant mortality begins to rise rapidly. Birthweight is determined by two major processes: duration of gestation and intrauterine growth rate. Low birthweight is caused by either a short gestation period or retarded intrauterine growth (or a combination of both). The relationship between these processes and the outcome of low birthweight are complex: not all preterm births result in low birthweight babies, nor does IUGR directly correlate to birth weight. However, it is clear that low birthweight live births do have a higher risk of death in the first year of life than babies of normal birthweight (i.e. 2,500g+). Furthermore, this is not the only consequence of low birthweight. It can also cast long shadows into adult health status with associations having been shown between low birthweight and adverse health in later childhood and adulthood, including deficits in growth, cognitive development, diabetes and heart disease.

In the current UK policy context, there is some emphasis on combating health inequalities at an inter-generational level and, as part of this process, giving every child a healthy start in life is accorded a high priority. One of the two government headline national targets on health inequality is to reduce inequalities in infant mortality. As low birthweight is a leading cause of infant mortality, preventing or ameliorating it is an important policy objective.

Lancashire Results

In simple numerical terms just over 1,390 low birthweight live births were recorded in the Lancashire sub-region in 2004 (Table 1). This represented about 22% of the North West Region total or 2.9% of those in England and Wales. By district the number of low birthweight live births was greatest in Blackburn followed some way behind by Preston, and lowest in Fylde and Ribble Valley. The data covers six years, a period probably to short to identify real trends but at face value between 1999-2004, whilst there was an apparent increase in the number of low birthweight babies in England and Wales of nearly 1,480 or 3.1% (after falling over the first half of the period), the number in Lancashire increased by 90 or 6.8%. There were quite large variations between local districts. Seven Lancashire districts recorded rates of increase above the national average, being particularly marked in Hyndburn, Blackpool and Burnley. Conversely, Fylde and Ribble Valley together with the two Central Lancashire districts of Preston and South Ribble recorded significant reductions in the number of low birthweight babies.

The published data, as outlined in Table 1 above, give the number of live births of low birthweight in an area but these on their own do not facilitate useful comparisons between areas due to differences in the size of resident populations and in the total numbers of live births occurring in one area as compared with another. To facilitate such a comparison the number of low birthweight live births has been expressed as a percentage of all live births in each area. The information for the denominator, i.e. the total number of live births, has been taken from another ONS publication entitled Key Population & Vital Statistics. This source provides data on the number of live births occurring in a given year but can also include some late registrations of births occurring in the previous year. The Low Birthweight Live Births data does not include these late registrations. However, whilst the two data sources are not wholly compatible, the cumulative effect is quite small and does not detract unduly from the broad conclusion given below based on the data in Table 2.

In 2004 babies born weighing less than 2,500g accounted for about 7.6% of all live births in England and Wales, a rate that appears to have been fairly stable over recent years. The equivalent rate for the Lancashire sub-region at 8.2% was notably higher but also represented a significant improvement over the previous year and an apparent reversal of the local trend over recent years, which had resulted in some deterioration in Lancashire relative to the position in England and Wales. At the more local level a rather mixed and in some instances a somewhat disturbing pattern is evident. This can best be illustrated by ranking each district in terms of its low birthweight rate out of the 374 local district areas throughout England and Wales. On this basis, in 2004 eight Lancashire districts (compared with six in the previous year) had low birthweight rates well below the national average and the top three of these – Fylde, Ribble Valley and Chorley are ranked within the top 25% of authorities in England and Wales. However, in ranked terms, Blackburn with Darwen with a low birthweight of 10.9% of all live births in 2004 was ranked not only the poorest performing district in Lancashire but also the second poorest (after Greenwich) out of all 374 districts in England and Wales. Burnley and Hyndburn join Blackburn in being amongst the lowest performing authorities in England and Wales and with Blackpool, Preston and Pendle, also rank within the poorest 15% range of districts. Generally speaking, those districts which exhibited a relatively low or below average rate of low birthweight cases in 1999 continue to improve their out-turns through to 2004. The improvement was particularly marked in the case of South Ribble. Conversely, for the most part, districts that performed poorly in 1999 continued to do so through to 2004, in the process recording higher rates in the later year. Amongst this group of authorities only Preston has recorded a reduction in the rate of low birthweight live births.

Figure 1 Live Births under 2,500 g, 2004 (numbers and rates)

Source ONS - Low Birthweight Live Births, 1999-2004/Key Population & Vital Statistics (KPVS)

The prevalence of low birthweight is known to vary by a wide range of factors including mother's age and general well-being, multiplicity, ethnicity and/or country of birth, smoking, nutrition, socio-economic position and a range of deprivation issues in general. Consequently, all these factors may contribute to the geographical variations noted above. It is beyond the scope of this article to offer detailed explanations or to seek to establish the relative importance of different factors. Suffice to say that analysis across a wide range of key social and economic indicators such as those relating to wages and incomes, housing conditions and measures of deprivation reveal the significant problems that continue to face many areas within Lancashire. It is therefore not wholly surprising that such difficulties are also reflected in relatively high rates of low birthweight babies in several districts. This point is further emphasised by the fact that such districts as Chorley, Fylde, Ribble Valley and South Ribble, which are by various indicators considered to be amongst the most affluent areas in Lancashire, also consistently recorded the lowest rates of low birthweight live births.

This page was compiled by Peter Kivell.

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