To our knowledge, this is the most up-to-date study on maternal mortality data in Spain. Although this maternal complication of pregnancy is recorded through the INE, there are no periodic analyses by health institutions that systematically reflect the trend or characteristics of this event in Spain. In this regard, the WHO stated that nations should maximize their efforts in strengthening health systems to collect high-quality data to respond to the needs and priorities of women and girls and ensure accountability to improve the quality of care and equity [17].
The maternal mortality rate in Spain is one of the lowest observed in countries in our region, with slight fluctuations year by year, which reflects, in part, the good health care provided for pregnancy, childbirth and postpartum complications and the universal access of the population to this health care. Other countries with similar or even higher levels of development, such as Norway and Canada, show maternal mortality rates in recent years between 5.1 and 12 deaths per 100,000 live births [18, 19]. The increase in the rate of this complication in these countries, such as Canada, was proposed to be the result of improvements in vital statistics registration data and due to the switch from the ICD9 to ICD10 when classifying this complication. In this regard, we do not know if maternal deaths are correctly quantified in Spain, although some authors claim that there may be inadequate identification and recording of maternal deaths in up to 40% of cases, which would reflect a clear underestimation of maternal mortality [20].
One of the most important findings of our research was the identification of the most common causes of maternal death in Spain. The most prevalent causes were hypertensive disorders of pregnancy, closely followed by obstetric haemorrhage. Other causes, in order of frequency, were other direct obstetric causes in up to 15% of the cases, amniotic fluid embolism in 10% of cases, infection and sepsis and obstetric thromboembolism; these data allows recognition of the problems that require greater optimization with respect to the allocation of health resources most necessary in Spain. These data do not differ much from those previously published by Fernandez et al. [21], who reported that the most prominent causes of maternal death in Spain were hypertensive disorders of pregnancy and postpartum complications in 22.6% and 23.3% of cases, respectively.
A descriptive analysis of the causes and trends of maternal mortality in Spain during the period between 1999 and 2015 also indicated that the most common causes responsible for this perinatal event were, in order of frequency, obstetric haemorrhage and hypertensive disorders of pregnancy [22]. The most relevant research on maternal mortality at the international level was published in 2015, in which a global and regional review of data from 186 countries during the 1990–2015 period identified the 8 main causes of maternal death. The results of the study indicated that, overall, obstetric haemorrhage is the most frequent cause of maternal death in most countries and that it is potentially avoidable with adequate obstetric management as well as the use of appropriate health resources [23].
Our results showed differences in the rate of this complication among the different regions of Spain where delivery occurred. The Chartered Community of Navarra and the Basque Country had the lowest rates while Melilla and Ceuta had the highest rates in the national territory. We do not know the underlying reasons for this situation, although possible factors include greater immigration from Africa in southern regions of Spain and each region having its own health system independent of the rest of the national territory. The distinguishing characteristics of different populations, the influx of immigrants with certain profiles and the inequality in the health benefits of each nation could justify the existence of health inequities in general and in reproductive health specifically among citizens of European countries, as was observed in this study [24, 25].
Maternal age could play an important role in the risk of maternal death, although its influence on this perinatal outcome was not specifically analysed. The group of women aged 40 years or older had a crude risk on the order of 3 to 5 times higher than that observed for women in other age groups in Spain during the study period. The risk of adverse perinatal events and complications during pregnancy is significantly increased with maternal ages greater than 40 years [26, 27]. Sheen et al. [28] pointed out that women in the age group of 45 years or older were those who had a greater risk of caesarean delivery, preeclampsia, postpartum haemorrhage, gestational diabetes, puerperal thrombosis and hysterectomy as severe complications of pregnancy.
When observing maternal death rates by maternal origin, the results of this study revealed very relevant findings regarding its influence on this pregnancy complication. First, the rates of maternal death were higher in the HDI groups comprising less developed countries, especially group 4 (very low HDI), with a crude risk 3 to 4 times higher than that for group 1. Regarding the continent of origin, with respect to European pregnant women, the rest of the women had higher rates of maternal death, more markedly for those whose continents of origin were Asia and Africa. This finding was already suspected due to previous publications in which maternal death and severe acute maternal morbidity events occurred more frequently in foreign women from less developed countries [13, 29].
Through linear regression analysis, we were able to verify that the lower the HDI and the higher the GII of the country of maternal origin, the higher was the maternal death rate, revealing how important it is to conduct further research on these aspects of development by classifying the origin of immigrant women in our country. In addition, when performing multivariate regression analysis adjusted for different covariates, we observed that a decrease of 0.01 points in the maternal HDI score generates a significant increase in the risk of maternal death. This allows a more accurate calculation of the added risk that a patient has of dying from pregnancy complications as a function of variations in this variable.
The HDI of the country of maternal origin simplifies and captures very important sociodemographic and economic characteristics regarding the development of each nation and provides a quantitative dimension. This could explain why its use may be valuable when analysing the specific risk of immigrant pregnant women suffering certain complications of pregnancy in developed countries, such as Spain, because maternal origin and various social determinants, such as family income, education level, degree of social exclusion and adequate access to emergency health services and pregnancy monitoring, have a very influential role in pregnancy outcomes [15, 30, 31].
Regarding the limitations of this study, we recognize that there are several. First, as previously mentioned, it is unknown whether all maternal deaths were correctly reported to the INE during the study period in Spain and whether this issue would result in an underestimation of the rates of this complication. Furthermore, for unclear reasons, there was also a nonnegligible percentage of maternal mortality cases with unspecified causes. As unspecified cases were very infrequent, it is possible that there would not be differences in terms of the characteristics of the pregnant women and the causes of maternal death when comparing higher HDI groups with lower HDI groups. In addition, in the multivariate analysis, the fact that there were relationships that were not significant can be explained by the fact that there were very few deaths with respect to the large number of births without mortality; therefore, the proportion of maternal deaths in all the groups analysed was very small, and it was difficult to find significant differences. Another limitation of our multivariate analysis model was the lack of adjustment for relevant variables, such as maternal age, body mass index, type of health care centre or pre-existing maternal conditions that are of interest in the study of maternal mortality.
Last, cases that fell within the definition of late maternal death and those that corresponded to the death of a woman from direct or indirect obstetric causes more than 42 days but less than one year after termination of pregnancy were not included [32]. These cases are equally important due to the very serious social connotations and the severe impact that the death of the mother produces on families.