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Maternal characteristics and neonatal mortality in Brazil

Most births (69.3%) were concentrated in the 20-34 years old age and the risk of neonatal death was lower in this
group. The lowest NMR was found in the group of mothers between 25 and 29 years of age. The choice of having children
later in life due to cultural and career changes in the lives of women has pushed the average age of childbirth higher.
Mothers less than 15 years of age and those older than 40 years had the highest risks of neonatal mortality.
The boxplot on Figure 4 shows how the standard deviation is increased in the neonatal death group, even though the
large amount of women 20-34 years of age strongly pushes the average to a center and the deviation to a smaller range. As
69.3% of the mothers were between 20 and 34 years old, the standard deviation shift is high. No differences were found
in median age and mean age between the neonatal death group and the all mothers group.
The last visualizations (Figures 5) are three decision trees (James, Witten, Hastie et al., 2003). The middle boxes
contain the NMR and the percentage of the group within the sample. The node boxes on the right contain only the
NMR for each combined feature. The results reveal higher NMRs among older mothers, unmarried mothers, and
those with no schooling compared to mothers younger than 35 years of age, married mothers, and those with 12 or
more years of schooling. The NMR was 17% higher among unmarried mothers compared to married mothers. In
the analysis of combined features, the NMRs were higher among older mothers even when they had a higher level
of schooling. These higher rates among older mothers were similar to those found among younger mothers with no
schooling, suggesting an important influence of extremes of age on neonatal mortality in Brazil. In the analysis of
marital status and mother’s age, higher NMRs were found among older (35 years or more) unmarried mothers. The
NMR was also high in youngest group (10-19 years of age) and this result was more unfavorable among unmarried
mothers. Indeed, the NMR was higher among unmarried mothers in all age groups. In the analysis of schooling and
marital status, higher NMRs were found among married and unmarried mothers without schooling, with higher rates
found among the married mothers. The lowest NMR (4.16) was found among married mothers with 12 or more years
of schooling. The majority of mothers (82.1%) had between 1 and 11 years of schooling. In this group, the NMR was
lower among the married mothers (5.31) compared to unmarried mothers (6.0). This decision tree also showed that
the mothers with no schooling only accounted for 1.3% of the sample. Although this proportion is small, it represents
nearly 2,600 neonatal deaths.

Figure 4. Boxplots of the mother’s age at childbirth, Brazil, 2006-2016. Source: SIM, SINASC, 2006-2016.

28 International Journal of Population Studies | 2019, Volume 5, Issue 2