Reliable data on maternal mortality are lacking in many countries due to underreporting and misclassifications of deaths. 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 accidental or incidental causes. Even where deaths are derived from a civil registration system with complete coverage, maternal deaths may be missed or not correctly identified, thus compromising the reliability of such statistics. In that context, underreporting or misclassification may be due to reasons such as inadequate understanding of ICD (International Classification of Diseases) rules; death certificates completed without mention of pregnancy status; desire to avoid litigation; desire to suppress information (especially as related to abortion deaths). Underidentification of maternal deaths is more common among early pregnancy deaths because they are not linked to reportable birth outcome. Also, deaths in the later postpartum period are less likely to be reported than early postpartum deaths. Maternal deaths at youngest and oldest ages are also more likely to remain unidentified.
When maternal deaths are derived from data collected in censuses, surveys, or demographic surveillance and the causes of reproductive-aged female deaths are identified based on interviews with family or community members, misclassification is common. For example, some deaths may be identified as maternal deaths even if they were due to accidents or injuries.
Results based on censuses or surveys may need to be adjusted for underreporting of births and deaths declared in the census and for distortions in the age structure. However, it is considered that the proportion of maternal deaths among all deaths of females of reproductive age is not significantly underreported, and therefore, this proportion may be used to estimate maternal mortality.
Estimates of maternal mortality obtained from household surveys have wide confidence intervals, making it difficult to monitor changes over time and to assess differences between population groups.
In countries where data on maternal mortality are suspected to be inadequate, it is important to interpret indicators of maternal mortality within the context of other maternal health indicators, such as presence of skilled health personnel at delivery and antenatal care.
Use of contraceptive methods may be underreported, especially where use of traditional methods or use of contraceptive sterilization are common. In order to reduce underreporting, the respondents should be reminded of various types of contraceptive methods.
Reliable statistics on abortions are not easily available. Abortions that are spontaneous and do not result in further complications are rarely reported. Induced abortions are also underreported, especially in countries with laws that restrict access to abortion.