Narrowing social inequalities in health? Analysis of trends in mortality among babies of lone mothers
Margaret Whitehead, Frances Drever
Policy and Development Division, King's Fund, London W1M 0AN
Margaret Whitehead, visiting fellow
Social and Regional Division, Office for National Statistics, London SW1V 2QQ
Frances Drever, statistician
Correspondence to: Dr M Whitehead, The Old School, Ash Magna, Whitchurch, Shropshire SY13 4DR margaret@ashmagna.demon.co.uk
Abstract
Objectives: To examine trends in mortality among babies registered solely by their mother (lone mothers) and to compare these with trends in infant mortality for couple registrations overall and couple registrations subdivided by social class of father.
Design: Analysis of trends in infant death rates from 1975 to 1996 for the three groups. The data source was the national linked infant mortality file, containing all records of infant death in England and Wales linked to the respective birth records.
Setting: England and Wales.
Participants: All live births (n=14.3 million) from 1975 to 1996; all deaths of infants from birth to 12 months of age over the same period (n=135 800).
Main outcome measures: Death rates in the perinatal, neonatal, and postneonatal periods and for infancy overall.
Results: For the babies of lone mothers infant mortality has fallen to less than a third of the 1975 level, with a clear reduction in the gap between the mortality in these babies compared with all couple registrations: the excess mortality in solely registered births was 79% in 1975 reducing to 33% in 1996. Most of the narrowing of the sole-couple differential was associated with the neonatal period, for which there is now no appreciable gap. For couple registrations analysed by social class of father, infant death rates have more than halved in each social class from 1975 to 1996. The reductions in mortality were greater in the late 1970s and early 1990s. Infant death rates in classes IV-V remained between 50% and 65% higher than in classes I-II. Differentials between social classes were largest in the postneonatal period and smallest in the perinatal and neonatal periods. The gap in perinatal and neonatal mortality between the babies of lone mothers and couple parents in social classes IV-V has disappeared.
Conclusions: The differential in infant mortality between social classes still exists, whereas the differential between sole and couple registrations has decreased, showing positive progress in the reduction of inequalities. As the reduction in the differential was confined to the neonatal period these improvements may be more a reflection of healthcare factors than of factors associated with lone mothers' social and economic circumstances.
Introduction
Infant mortality is an important indicator of a population's health, and any social differentials in this indicator are regarded as unacceptable. The traditional way of analysing social trends in infant mortality has, however, become increasingly problematic: growing numbers of infants are excluded from such an analysis, not least the babies of lone mothers. The size of this potentially vulnerable group has increased from 5% of births in 1975 to 8% in 1996. In Britain a high proportion of lone mothers live in poverty, [1] [2] and their children face socioeconomic disadvantage and have higher risks of health problems such as accidents and infections. [3] [4]
We analysed trends in mortality in babies of lone mothers and compared these with mortality trends in babies of couple parents from different social classes, whether married or not.
Methods
The numbers of live births, stillbirths, and early neonatal, late neonatal, and postneonatal deaths for each year from 1975 to 1996 were obtained from the Office for National Statistics for babies born inside marriage, babies born outside marriage but jointly registered by both parents, and babies born outside marriage registered solely by the mother.
Since 1975 registrations of infant deaths in England and Wales have been linked to birth records, which means that the more detailed information collected at birth on a range of sociodemographic factors can be used in the analyses of deaths. All social class analyses are based on a 10% sample of coded records. Data relating to births outside marriage registered solely by the mother were placed in a separate category.
Mortality for various ages within infancy was calculated from 1975 to 1996 for the babies registered solely by the mother and for each social class. Data for births inside marriage were combined with those outside marriage jointly registered by both parents--the combination referred to here as ``couple registrations'' or ``couple parents.'' Data for social class I were combined with class II and those for class IV with class V to increase the robustness of the calculated rates. Three year moving averages were calculated for the same reason. Confidence intervals around the mortalities were calculated by the methods of Breslow and Day.[5]
Infant mortality, England and Wales, 1975-96 (3 year moving averages). Registrar general's social class I-II: professional, managerial, and technical occupations; IV-V: partly skilled and unskilled occupations; sole registered: babies whose birth is registered solely by the mother; all births: all births, regardless of type of registration. Data for social class for 1981 are not available because of industrial action by registrars in that year
Results
Mortality trends varied for each stage of infancy and by social grouping (figure) At the beginning of the period, mortality was highest for the babies of lone mothers followed by a gradient from classes IV-V down to classes I-II with the lowest mortality. Infant mortality fell steadily for the sole registration category until 1984 and remained stable until 1989, when the decline resumed. There was also a narrowing of the differential between the sole and couple registrations. In the mid-1970s infant mortality was 79% higher in the sole registrations compared with the couple registrations, and by 1996 this had reduced to a 33% excess (table).
Most of the narrowing resulted from greater improvements in mortality of solely registered births in the perinatal and neonatal periods from the mid-1970s and throughout the 1980s, and the difference was no longer significant by 1994-6 (table) in contrast with postneonatal mortality. The postneonatal mortality differential between sole and couple registrations has been large and has shown no tendency to narrow.
There has been only a little narrowing of the differential between social classes IV-V and I-II. In 1975-7 infant mortality was 64% higher in classes IV-V, since when it has fluctuated, but was still 52% higher in 1996. What is striking, however, is the clear reduction in the differential to a negligible amount between the infant mortality of the solely registered group and that of classes IV-V (table).
Discussion
This analysis shows an improvement in mortality in babies registered solely by their mothers. In absolute terms, infant mortality for this group has declined to a third of its 1975 rate. In addition, the mortality of babies in this group relative to other groups has fallen. Although infant mortality is still 33% higher than for couple registrations, the gap has reduced from an excess of 79%. Furthermore, there is now little difference between the death rates of solely registered babies and those of classes IV-V, in contrast with the findings of studies in the 1970s[6] and the 1980s.[7] Much of this improvement for the solely registered babies up to 1990 occurred during the perinatal and neonatal periods rather than the postneonatal period. Our results raise the possibility that improvements in maternal and neonatal health have been particularly beneficial for the babies of lone mothers or that their access to the relevant services has improved, or both.
Limitations of this study are, firstly, that some babies of lone mothers may also be included in the joint registration category, and these cannot be identified separately from published sources. This form of misclassification has probably not changed over the study period in a way that would affect the interpretation of trends. Secondly, the status of the baby at death may be different from that at birth, but this is unlikely to be an issue for most of the deaths occurring within 1 month of birth.
The research highlights the need for lone and unsupported mothers to be given every possible help after the birth of their babies, not just in the neonatal period but on a sustained basis.
We thank Jeremy Schuman, Office for National Statistics, for help in extracting the data on deaths.
Contributors: MW and FD jointly developed the idea for this study and worked on its design. FD carried out the statistical analysis, while MW took responsibility for reviewing the literature. They both then participated in the interpretation of the results and the writing of the paper.
Funding: None.
Competing interests: None declared.
1 Bradshaw J. International comparisons of support for lone parents. In: Ford R, Millar J. eds. Private lives and public responses: lone motherhood and future policy in the UK. London: Policy Studies Institute, 1998.
2 Shouls S, Whitehead M, Burström B, Diderichsen F. Trends in the health and socio-economic circumstances of British lone mothers over the last two decades. Popul Trends 1999;95:5-10. (16 March.)
3 Roberts I, Pless B. Social policy as a cause of childhood accidents: the children of lone mothers. BMJ 1995;311:925-8.
4 Wadsworth J, Burnell I, Taylor B, Butler N. Family type and accidents in preschool children. J Epidemiol Community Health 1983;37:100-4.
5 Breslow N, Day N. The standard mortality ratio. In: Sen P, ed. Biostatistics: statistics in biomedical public health and environmental science. New York: Elsevier, 1985.
6 Macfarlane A, Mugford M. Birth counts: statistics of pregnancy and childbirth. London: HMSO, 1980.
7 Leon DA, Vågerö D, Olausson OP. Social class differences in infant mortality in Sweden: a comparison with England and Wales. BMJ 1992;305:687-91.