Methodology

This page provides a brief overview of the methodology employed to produce the maternal mortality estimates for the period 2000-2020.
More detailed information can be found in the metadata or in Chapter 3 of the full report.

Definitions

A maternal death is defined as: the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management but not from unintentional or incidental causes.

A pregnancy related death is defined as: the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the cause of death (obstetric and non-obstetric); this definition includes unintentional/accidental and incidental causes.

Measures of maternal mortality

The number of maternal deaths is the number of maternal deaths in a population during a specified time period, typically one calendar year.

The maternal mortality ratio (MMR) is defined as the number of maternal deaths during a given time period per 100 000 live births during the same time period; thus, it quantifies the risk of maternal death relative to the number of live births.

The adult lifetime risk of maternal death for women in the population, defined as the probability that a 15-year-old girl (in the year of the estimate) will eventually die from a maternal cause. This indicator takes into account competing causes of death.

Data inputs

Sources for maternal and pregnancy related mortality

Civil Registration and Vital Statistics (CRVS)

Specialized studies on maternal mortality

Specialised studies on maternal mortality triangulated information from multiple sources, including, but not limited to, medical/hospital records, police records, surveillance systems, national registries, death certificates, censuses, medical autopsies, and administrative reviews to estimate the true number of maternal deaths. Two common examples of specialised studies are Confidential enquiries into maternal deaths (CEMD) and Reproductive Age Mortality Studies (RAMOS)

Surveys and other miscellaneous data sources for maternal mortality:

We also use population-based household surveys including the - Demographic and Health Surveys (DHS), and the - Multiple Indicators Cluster Surveys (MICS), which use the sisterhood method to identify deaths of women in the reproductive age and their causes. Additionally, national censuses which collect information on pregnancy related and/or maternal mortality are also included. Other input data sources not falling into one of the above categories are also included if they meet our eligibility criteria and are termed “Miscellaneous”.

Other sources used in maternal mortality estimation

Other sources of data used include live births and all-cause deaths to women aged 15-49 from UNDESA/Population Division’s 2022 revision of the World Population Prospects (WPP); estimates of deaths due to HIV from the Joint United Nations Programme on HIV/AIDS (UNAIDS); gross domestic product (GDP) per capita, measured in purchasing power parity (PPP) equivalent international dollars using 2017 as the baseline, generated based on data from the World Bank Group; general fertility rate from World Population Prospects 2022; and coverage of births attended by skilled birth attendant (SBA) from WHO and UNICEF Joint Skilled Birth Attendant database.

Data processing

Adjustments are made to the data to account for missed and misclassified data. Full details can be found in the report.

Statistical Methods

We use two models, for different purposes:

The BMis model: For countries that have eligible CRVS data, we use BMis – the Bayesian misclassification model to obtain CRVS adjustment factors, in order to account for errors in reporting of maternal death in the CRVS.
The BMat model: For all countries, we use a Bayesian maternal mortality estimation model to estimate the MMR for each country- year of interest.

In the BMat, the MMR for each country-year is modelled as the sum of the AIDS MMR and the non-AIDS MMR.

The models described above are broken down into global and one-country implementations. Model assumptions are the same for one-country and global models. The development of this new set up is motivated by the demand for computational efficiency, without loss of model accuracy, when updates for a specific country are needed due to new data availability or when data needs to be corrected.

To estimate MMR for country-years, we first use the BMis global model to obtain the fixed non-population-specific parameters. Secondly, we use multiple instances of the BMis one-country model to obtain adjustment factors for each country-year of interest. These adjustment factors are then applied in BMat global and BMat one-country runs. In the next phase we use the BMat global model to obtain the fixed non-population-specific parameters. Finally, we use multiple instances of the BMat one-country model to estimate the MMR for each country-year of interest.

Aggregation of Estimates

Regional maternal mortality estimates (according to the United Nations SDG, WHO, UNICEF, UNFPA, the World Bank Group and UNDESA/Population Division regional groupings) were computed.

The regional aggregate MMR was calculated as the weighted average of the MMR, where weights are based on the number of live births.
The regional aggregate lifetime risk of maternal mortality in a given region was calculated as the weighted average of the lifetime risk where the weights are based on the number of women aged 15-49 and the probability of surviving to age 15.

Maternal Mortality