In recent years, different authors have investigated factors related to infant mortality and maternal-infant health conditions. Regarding the influence of socioeconomic factors, the literature has shown that there are differences according to the place studied [17-19]. In the present study, besides macro-regions with medium MHDI being associated with death (p=0,036), maternal education, individually and jointly analyzed with the MHDI, showed association with the outcome of infant death in the first year of life, particularly for children of mothers with lower maternal education (p<0.001). In relation to other related factors, low maternal age; number of Prenatal Care Consultations; gestational age, weight, gender, congenital anomaly, and Apgar Index (5th minute) of the newborn showed association with IM (p<0.001) in the municipality of Porto Alegre from 2000 to 2017. These results corroborate previous studies that identified biological and prenatal care factors related to infant death [1, 20-22].
Although most mothers were between 18 and 34 years of age, the highest proportion of child deaths in the first year of life (1.5%) occurred among the children of those under 18. This age group presents a higher risk for complications, since younger women are still in the phase of physical and psychological development and, part of them, performing their studies in primary, secondary or even higher education [23, 24]. Single, legally separated or widowed women presented a higher risk of death than those married or in a stable union (RR= 1.69; CI95% 1.56-1.83). In literature, other studies have described that the condition of women without a fixed partner negatively affects the health of the mother and child, because it generates some degree of suffering for the woman, who may develop, among other conditions, depression, thus influencing the mother-baby interaction. Moreover, it represented a decrease in emotional and economic support for the family [25-27].
As for the type of birth, most women have had vaginal birth. However, the present study did not evaluate the temporal evolution of this variable, since it is known that this percentage has varied according to the year. Although the evidence does not show an association between cesarean section and a decrease in IM, the number of cesarean sections has been steadily increasing in both developing and developed countries [28, 29]. In 2015, for the first time in Brazil, the number of operative deliveries stabilized . The proportion of cesarean sections was higher in macro-regions with better MHDI scores. This ratio, according to different authors, could be explained by the preference for cesarean sections with higher socioeconomic level, white ethnicity and higher maternal education [30, 31]. Moreover, the most visible discrepancies are observed when comparing cesarean rates in public and private hospitals in several regions of Brazil [31, 32]. These rates in the private sector are significantly higher than in the public health system, exceeding 90% in some hospitals [33, 34].
The MHDI has proven to be an indicator that has a relationship with the variables studied. The lower the classification of the MHDI of the macro-region of maternal residence, the worse were the socioeconomic and demographic conditions. Previous studies that evaluated infant mortality in different regions or ethnic groups found similar results [18, 19]. Cruz and collaborators  observed that, in Brazil, women living in more developed regions have lower chances of having an early pregnancy. Approximately, an analysis conducted in Nigeria with population data found that lower maternal age, as well as lower education, especially of mothers who had deceased children showed association with child death . In this context, this same association is found with the worst maternal conditions observed in less developed or developing countries, as well as in regions with lower income and limited access to health services [3, 35].
In the same perspective, although studies show that prenatal care coverage in Brazil has increased by up to 98.7%, the percentage of women with less than 7 prenatal visits is frequent and may vary according to the region analyzed [36, 37]. Data regarding the city in this study showed an improvement of this indicator by 41.71% in the period from 2001 to 2017. However, it is known that this percentage varied according to interurban and health care differences, and there may be regions with adequate Prenatal Care Consultations above 80% and others below 65%. Although the present study did not specifically investigate the annual temporal evolution of prenatal care coverage, these percentages are similar to the results found for this variable.
Research that assessed the influence of the HDI of the maternal home region, when at birth, on health outcomes, showed that this indicator when low is associated with worse outcomes with respect to child neuropsychomotor development [39, 40] and also with higher infant mortality rates [19, 41]. In a study with data from 188 countries, Ruiz and collaborators  found that IM was correlated with low HDI and low inequality-adjusted HDI, with the latter being more strongly correlated than the former (Z = 2.524, p = 0.012).
Although higher maternal education does not guarantee protection for infant death in the first year of life, as shown in the analysis, schooling less than eight years of study represents a risk factor increasing the chance of death by 37 to 40%, both in the MHDI and its three components. That is, even though the higher maternal education level did not show statistical significance in reducing infant mortality in the present study, the low educational level showed an association with infant death. It is assumed that these results are attributed to the worst socioeconomic conditions of that mother and the social and community environment in which she lives with limited access to various resources and health services as well as worse conditions of basic sanitation [22, 42, 43]. Viellas and collaborators  found that in Brazil, women with lower education had less prenatal care coverage, fewer prenatal visits and higher utilization of public services. In contrast, they found that those with higher education used more specialized prenatal services, mostly in private services, with monitoring by the same professional throughout pregnancy. In this sense, prenatal care is a process of health education for women and their families, collaborating in the care of pregnancy and children, including, often, the beginning of health care for some individuals, especially adolescents .
However, other studies have shown that, in addition to socioeconomic conditions, higher maternal education has improved the child's health conditions and prevented infant mortality. The higher educational level of mothers, together with their better intellectual capacities, help in health choices, increase the understanding and use of information and improve the perception of health problems . They also invest in more health-beneficial behaviors, both at the individual and child levels, showing better adherence to health recommendations in terms of nutrition, exercise and reduction of harmful habits [46-49].
Some particular features of the study are worth highlighting. The study was a pioneer in the country in analyzing the relationship of the MHDI of the different regions of a municipality with infant mortality. It was also unprecedented in performing a parallel analysis of the influence of maternal schooling and MHDI on IM. Furthermore, it used two well consolidated health information systems in the municipality over an extended period of time (2000-2016), which provided a robust database with higher quality in its processing and analysis. This study was important because it revealed that maternal education was shown to be superior to the MHDI as a predictor of infant mortality, reinforcing that when schooling is very low, it can contribute to risky behaviors, and perhaps in addition to being a social indicator, it should be considered a health indicator for the child, as it helps in the health choices of the child’s mother and adherence to recommendations. With a health indicator, the mother's educational level could guide the elaboration of public policies, assisting in the screening of risk groups not only by the region of residence, but also by the individual maternal conditions and thus enabling more agile and targeted actions for these individuals of greater risk.
On the other hand, the study presented some limitations. Among them, the non-use of the race/skin color variable, as it was incomplete in some of the years analyzed, and the use of secondary data with pre-established variables and lack of information on serious diseases and maternal characteristics (income, maternal weight and smoking) and more specific neonatal characteristics (breastfeeding). One hypothesis to explain that MHDI did not present a higher risk of death, as well as what has already been evidenced in the literature is that just like the HDI, the MHDI when analyzed in macro-regions can hide areas of low development and social vulnerability. This could have influenced the analyses since the MHDI values are distributed to the macro-region, not including in the analytical process the micro-regions classified with low or very low MHDI. Porto Alegre currently has 335 micro-regions , of which many have very low MHDI values, especially when analyzing the education component. However, the database used did not have a list with the address codes for each micro-region.