Examining the impact of introducing ICD-MM on observed trends in maternal mortality rates in the UK 2003-13

Background
The causes of maternal death are now classified internationally according to ICD-MM. One significant change with the introduction of ICD-MM in 2012 was the reclassification of maternal suicide from the indirect group to the direct group. This has led to concerns about the impact of this reclassification on calculated mortality rates. The aim of this analysis was to examine the trends in maternal deaths in the UK over the past 10 years, and to investigate the impact of reclassification using ICD-MM on the observed rates.
Methods
Data about all maternal deaths between 2003-13 in the UK were included in this analysis. Data about maternal deaths occurring prior to 2009 were obtained from previously published reports. The deaths of women from 2009-13 during or after pregnancy were identified through the MBRRACE-UK Confidential Enquiry into Maternal Deaths. The underlying causes of maternal death were reclassified from a disease-based system to ICD-MM. Maternal mortality rates with 95% confidence intervals were calculated using national data on the number of maternities as the denominator. Rate ratios with 95% CI were calculated to compare the change in rates of maternal death as per ICD-MM relative to the old classification system.
Results
There was a decrease in the maternal death rate between 2003-05 and 2011-13 (rate ratio (RR) 0.65; 95% CI 0.54-0.77 comparing 2003-5 with 2011-13; p=0.005 for trend over time). The direct maternal death rate calculated using the old classification decreased with a RR of 0.47 (95% CI 0.34-0.63) when comparing 2011-13 with 2003-05; p=0.005 for trend over time. Reclassification using ICD-MM made little material difference to the observed trend in direct maternal death rates, RR=0.51 (95% CI 0.39-0.68) when comparing 2003-5 with 2011-13; p=0.005 for trend over time.
Conclusions
The impact of reclassifying maternal deaths according to ICD-MM in the UK was minimal. However, such reclassification raises awareness of maternal suicides and hence is the first step to actions to prevent women dying by suicide in the future. Recognising and acknowledging these women’s deaths is more important than concerns over the impact reclassification using ICD-MM might have on reported maternal death rates.