Saving Mothers' Lives: - Public Health Agency for Northern Ireland

xxvi
Introduction and aims, objectives and defi nitions used in this Report
Furthermore, in the United Kingdom maternal mortality rates can be calculated in two ways:
• Through offi cial death certifi cation to the Registrars General (the Offi ce for National Statistics (ONS)
and its equivalents), or
• Through deaths known to this Enquiry. The overall maternal death rate is calculated from the
number of Direct and Indirect deaths.
ONS data are based on death certifi cates where the cause of death is directly or secondarily coded for a
pregnancy-related condition such as postpartum haemorrhage, eclampsia etc.
For the past 50 years the Enquiry has calculated its own maternal mortality rate as the overall number
of maternal deaths identifi ed by the proactive case fi nding methodology used by this Enquiry has always
exceeded those offi cially reported. This is because not all maternal deaths are recorded as such on
death certifi cates. For example, a large proportion of women known to the Enquiry who died of preexisting
medical conditions infl uenced by their pregnancy, for example cardiac disorders, epilepsy and
some malignancies, were excluded from the offi cial statistics. Other women excluded in offi cial data are
those who required long term intensive care and whose fi nal cause of death was registered as a non
pregnancy condition such as multiple organ failure even though the initiating cause was an obstetric event.
Conversely, the maternal deaths known to the Registrars General may include Late deaths as it is not
possible to identify from the death certifi cate when the delivery or termination occurred.
In order to aid the international comparison of the UK data with those from other countries calculated by
using the ICD defi ned Maternal Mortality Ratio, this Report has also calculated the overall UK MMR as
well as the more complete Enquiry maternal mortality rate. These are shown in Chapter 1. However, when
making such comparisons, it is important to note two points:
• The criteria used by the UK assessors for Indirect deaths are far more inclusive than those used in
other countries. For example in this Enquiry all cases of cardiac disease, asthma and epilepsy are
coded as Indirect, as are cases of suicide unless obviously occurring in women with a longstanding
previous psychiatric history.
• Case ascertainment is lower in the vast majority of other countries because they do not undertake
such comprehensive enquiries.
Case ascertainment
The role of the Offi ce for National Statistics
Since the introduction of a new Offi ce for National Statistics (ONS) computer programme in 1993, all
conditions given anywhere on the death certifi cate are now coded enabling a more extensive search of
death entry information to identify all conditions listed which suggest a maternal death. In the past this has
helped in improving case ascertainment, with a number of previously unreported deaths being identifi ed.
Fortunately for this Report the ONS record linkage study described below has identifi ed very few additional
cases of Direct or Indirect deaths. This is a reduction in the already small degree of under-ascertainment
calculated for previous Reports.