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Trends in Infant Mortality
Reference has been made in each of the three preceding Annual Reports to the unusual pattern
of infant mortality in Hillingdon which is very different from that which would be expected in an
Outer London Borough with relatively few areas of unsatisfactory environmental conditions and
with health services whose quality is above average. When Mr. M. J. Southgate took up his duties
as statistician he was asked to investigate the statistical validity of the conclusions reached, and the
following comments are based on his report.
The infant mortality rate has always been considered to be an extremely important indication
of the general health of a population. Since the inception of the London Borough of Hillingdon in
1965 it has been observed that this rate has been on the increase, only two years (1970 and 1972)
showing a decrease on the previous year's figure. It was realised that any conclusions reached would
carry greater weight if Hillingdon was not considered in isolation and the corresponding figures for
the whole of England and Wales together with those for the Greater London Council area as well
as several other London boroughs were also obtained.
In Research Report 9 of the Intelligence Unit of the Greater London Council comparisons were
made between boroughs based on six parameters in the 1966 census as follows:
Housing conditions Population and household structure
Housing Tenure Birth place characteristics
Socio economic characteristics Characteristics of the young transient population
The intention was to group a particular borough with those most closely similar to it based on these
parameters. By this analysis Hillingdon is thought most closely to resemble the London Boroughs
of Bexley and of Havering. There was also some evidence from overseas that the presence of a
major airport could be related to adverse trends, and the statistics for the London Borough of
Hounslow were therefore also included.
The analysis showed that the average figures for infant mortality, neo-natal mortality and perinatal
mortality for the six years under review were indeed lower in Hillingdon than in any of the other
populations studied. The average figure for the still-birth rate in Hillingdon was the third lowest, but
in all rates reviewed the average figure was less than in Greater London, in England and Wales and
in Hounslow. This highly satisfactory result becomes less encouraging when it is appreciated that
the variation around the average figure is considerably greater in Hillingdon than in most of the other
areas studied, and that Hillingdon's good performance largely results from advantages obtained
before 1969. The averages for the years 1969 to 1971 are all higher than those for all seven years,
and substantially higher than those for the initial four years. The analysis shows that the national
trend in infant mortality is towards a reduction in the infant mortality rate. In Greater London there
is as yet no definable trend, and this is also the case in the London Borough of Hounslow. In
Hillingdon, however, there is a significant upward trend in infant mortality. As has been pointed
out this upward trend is particularly noticeable when the earlier results are compared with more
recent ones, whereas in Havering an exactly reverse pattern appears with an initial increase in rate
being followed by a very significant decrease. The London Borough of Bexley does show a similar
pattern to Hillingdon except that the increase is far less marked and in fact not statistically significant
when all seven years are examined together.
It is concluded that the upward trend in infant mortality in Hillingdon is a statistically significant
one and is not accounted for by the proximity of a major airport, although the hypothesis that stillbirths
rise in the vicinity of a major airport is not excluded by this data, since the average rate in
Hillingdon is not as favourable as that for other rates, whilst the figure for Hounslow is greater than
the average for still-births in the Greater London area generally.
Detailed analysis within Hillingdon
An analysis of the particular rates shows that increases in the infant mortality have been
accompanied by increases in the neo-natal and early neo-natal mortality rate. This suggests that any
adverse factors which may be operating do so principally in the first month of life.
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