Infant Mortality
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Inequalities in Infant Mortality Project Briefing Paper 1 Infant mortality: overview and context Jennifer J Kurinczuk, Jennifer Hollowell, Peter Brocklehurst, Ron Gray National Perinatal Epidemiology Unit, University of Oxford June 2009 1 Introduction The information presented in this paper comes largely from the analysis of routinely published Since 2000 the Government has made tackling data from the Office for National Statistics health, social and educational inequalities a (ONS), now the UK Statistics Authority. Data public service priority by setting public service are presented for the most recent year available agreement (PSA) targets which focus on these which, at the time of writing, was 2007; long areas. Health inequalities in children are the term trends are presented by five yearly figures specific focus of Target 11 as identified in where appropriate. For much of the information the 2002 spending review1; the aim being to presented there are complex underlying narrow the health gap between socio-economic relationships which it is not possible to explore groups and between the most deprived areas using published data. Care must therefore be and the rest of the population, in childhood exercised in the interpretation of these figures. and throughout life. The 2004 spending review For example, young women whose infants have reaffirmed this PSA target by re-stating it as “To high rates of mortality are, in addition to their reduce inequalities in health outcomes by 10% relative youth, also more likely to be unmarried by 2010 as measured by infant mortality and life and to be of lower socioeconomic status with a expectancy at birth.”2 The objective of the infant higher prevalence of associated risk factors for mortality element is defined in Figure 1. infant mortality. From the data presented here it is not possible to disentangle which of these Figure 1. Infant Mortality PSA Target2 factors is responsible for the higher risk of infant mortality and which are confounders. A simple “Starting with children under illustration of this complex situation is given in one year, by 2010 to reduce the birth statistics of the relationship between by at least 10% the gap in maternal age and marital and birth registration mortality between the routine status (see section 2.5). Definitions of terms and manual groups and the used in this paper are given in the glossary at population as a whole. The the end. baseline is 1997-99.” 2 The changing pattern of birth The Department of Health has identified five statistics key actions for the successful delivery of the infant mortality target. One of these actions is to In 2007 in England and Wales there were “develop a plan to strengthen the evidence base 690,013 live births and 3,598 stillbirths born to about interventions to reduce infant mortality.”2,3 682,999 women; the birth rate rose again for the To achieve this, the Department of Health has sixth consecutive year; and the total fertility rate commissioned a series of systematic reviews was at an average of 1.92 children per woman. of the evidence from the National Perinatal This is the highest fertility rate for 34 years. The Epidemiology Unit (NPEU). As part of the review total number of live births is now at its highest process the NPEU will also produce a series of since 1991. briefing papers, of which this is the first. The recent increase in the overall birth rate The aim of this paper is to provide a background has largely been driven by the increase in the to the evidence review process by presenting birth rate of women in their thirties and forties an overview of recent trends in infant mortality with the recent reversal in declining birth and setting this in the context of changes in the rates for women in their twenties making a maternal and infant population seen over recent smaller contribution.4Other factors include the decades in England and Wales. contribution to births made by women born 1 outside the UK and in particular specific groups Figure 3. Twining rate per 1,000 of women born outside the UK who have higher maternities* England and Wales, 1938 to fertility rates than UK-born women. 2007** 16 2.1 Trends in maternal age at birth 14 s ie The past 40 years has seen profound changes in it rn 12 the profile of the fertility of women of different te ma 10 ages (Figure 2). From the mid-1970s onwards 1,000 1,000 8 the birth rates of women over the age of 30 r pe have consistently increased, which is in marked 6 te ra contrast to the decline in birth rates of women 4 ng between the ages of 20 and 30 years which was ni in 2 st evident until a reversal at the start of the 21 Tw century. 0 8 38 19 1944 1950 1956 1962 196 1974 1980 1987 1993 1999 2005 In the 1960s the largest number of births was Year of maternity to women aged 20-24 years. The 1970s saw the *Refers to the number of women delivering predominance of births to women 25-29 which **Data for 1981 are not included as they were incomplete continued until 1999 when they were outstripped due to industrial action by registration staff that year for the first time by women aged 30-34 years. In The triplet and higher order multiple birth rate 1985 only 27% of births were to women 30 years (Figure 4) is even more strongly influenced and over compared with 48% in 2005 (Figure by patterns in treatment with IVF and related 2). Nineteen percent of births in 2005 were to assisted reproductive technologies (ART). The women 35 years and over compared with only peak triplet and higher order birth rate was 5 per 8% in 1985. 10,000 maternities in 1998 when it was nearly five times the rate seen in the 1970s. The decline The effect of the increasing fertility of ‘older’ in the rate followed a change in IVF clinical women is reflected in the average maternal age practice and the introduction of the policy of at first birth which has risen steadily from 24.8 two-embryo transfer (apart from in exceptional years in 1985 to 27.7 years in 2007. circumstances) by the Human Fertilisation and Embryology Authority (HFEA) in 2001. Figure 2. Maternal age at birth, maternities Figure 4. Triplet and higher order rate per in England and Wales, 1985 to 2005 1,000 maternities* England and Wales, 100% 1938 to 2007** 80% 0.50 40+yrs 0.45 35-39yrs s ge 60% 0.40 ie ta 30-34yrs it rn cen 0.35 r 25-29yrs 40% te Pe 20-24yrs 0.30 ma <20yrs 20% 0.25 1,000 1,000 r r 0.20 pe 0% te 0.15 1985 1990 1995 2000 2005 ra t le 0.10 Year of maternity ip Tr 0.05 0.00 2.2 Multiple births 4 9 1938 1944 1950 1956 1962 1968 197 1980 1987 1993 199 2005 In 2007, 15 in every 1,000 women having a Year of maternity baby in England and Wales delivered twins and * Refers to the number of women delivering 2 in every 10,000 delivered triplets or a higher **Data for 1981 are not included as they were incomplete order multiple birth. This represents the highest due to industrial action by registration staff that year rate of twining since the collection of records 2.3 Birth weight and gestational age about multiple births began in 1938 (Figure 3). The increase in twinning since the mid-1970s The distribution of birth weight has shifted over represents the combination of the effects of time with a slight increase in the proportion of increasing maternal age at conception and low birth weight babies (<2,500g) from 6.9% increasing use of infertility treatment, particularly in 1985 to 7.6% in 2005 (Figure 5). However, in vitro fertilisation (IVF) with the replacement recent data are suggestive of a decline with 7.3% of two or more embryos; in 2004 23% of IVF of live births in 2007 born weighing less than maternities resulting in a live birth were multiple 2,500g. births.5 2 Infant mortality: overview and context Figure 5. Birth weight distribution* of live were extremely pre-term (<28 weeks). Just less births, England and Wales, 1985 to 2005 than 1 in 20 (4.3%) were born at 42 weeks or 6 100% later. 90% 2.4 Migration patterns and the impact 80% 70% <1,500g on births 60% 1,500-1,999g ge Increases in births, decreases in deaths and ta 50% 2,000-2,499g changes in the pattern of international migration en rc 2,500-2,999g 40% into and out of the United Kingdom have all Pe 3,000-3,499g 30% contributed to recent increases in the size of the 3,500+g 20% general population. The number of births has increased partly due to rising fertility among UK- 10% born women and partly because of an increase 0% 1985 1990 1995 2000 2005 in the number of women of childbearing age entering the country as temporary visitors or Year of birth permanent migrants. This has had a substantial *Excludes births where the birth weight was not recorded impact on the trends in the proportion of births The shift in low birth weight is reflected in a to women who were themselves born outside slight increase in the proportion of live births the UK. In 1985 just over 12% of live births in born 3,500g or above from 36.8% in 1985 to England and Wales were to women born outside 39.5% in 2005.