Findings from this study showed, that although U5MR in the SSGZ (73 per 1000 live births) was less than the national U5MR (132 per 1000 live births), it was however higher than the global U5MR (38 deaths per 1000 live births) which indicates a need for further interventions to meet the sustainable development goals target of 25 deaths per 1000 live births. The study identified maternal overweight, maternal primary and secondary education levels, male gender, high birth order, and small birth size as significantly associated with increased odds of U5M, while ≥ 7 household members and having 2 U5s in the household were protective. Of the factors identified, low birth size alone accounted for over 47% of the U5M risks. These findings emphasise the role of socioeconomic and proximate level factors in elevating U5M in SSGZ, Nigeria, and support the Mosley and Chen's framework. After adjusting for confounding in model 2 the modification to odds ratio suggests that multiple socioeconomic factors interact to influence the magnitude of the U5M risk, while the change in odds of mortality for socioeconomic factors in the presence of proximate factors support Mosley and Chen’s idea that socioeconomic factors exert their effect on U5M through proximate factors [24].
Though the evidence from this study has not been reported previously, the difference in the U5MR of the SSGZ from the national rates and by sociodemographic characteristics supports the suggestions by researchers [18, 31, 32, 33, & 34] that variations exist in U5MR by GZ and sociodemographic characteristics. This reduced U5MR in the SSGZ compared to other regions could be explained by the differences in economic, climatic, and social conditions across the GZs of Nigeria. The SSGZ is home to major industrial centres and receives the largest budgetary allocation increasing resources available to provide basic amenities [35] and has a higher average human development index (0.635) [36] which culminates in a higher survival rate. It also has a longer rainy season and higher precipitation with relatively milder temperatures promoting the variety and availability of food year-round. Finally, the majority of SSGZ residents are Christians which is less restrictive on mothers’ autonomy, access to education, contraceptives, and employment outside the home that could impact their knowledge of appropriate childcare practices, and access to resources. However, when compared to global U5MR the higher U5MR may be explained by the higher level of poverty in Nigeria where 40.1% of the population, live on less than $1.90 per day, [37] and fewer healthcare workers for the population density (1.55 health worker per 1000 people) less than the recommendation of the World Health Organization (WHO) of 4.45 per 1000 [38]. It is also affected by environmental degradation from crude oil spillage and pollution which have been implicated in the poor living conditions linked with child mortalities [39].
The association between maternal education and U5M for the SSGZ was a departure from the findings of other researchers [17, 40, 41, 42]. The increased odds of U5M among mothers with primary or secondary education could be due to a combination of poverty and poor quality of education. Inadequate funding for education (5.4% of the annual budget), poor policy implementation and regulation, and corruption negatively affects the quality and quantity of educational resources in Nigeria [43]. The low level of participation of women in the labour force (48.4%) [44, 45] due to high unemployment and the traditional role of mothers as homemakers may result in a lack of resources to implement knowledge to improve child survival. Also, women with a higher level of education are less likely to engage in certain types of jobs, increasing unemployment among this group [46].
The increased odds of U5M among overweight mothers is consistent with the findings of Creswell et al (2012) [47] but contradict Khan & Awan (2017) [48]. Maternal overweight increases the risk of negative health outcomes for newborn through complications such as pre-eclampsia and diabetes which increase the risk for birth complications, restricted intrauterine growth, congenital anomalies, and birth trauma [49, 50], which is further exacerbated by the unavailability of facilities and resources to manage high-risk births. Also, mothers are the major decision-makers for family nutrition, thus poor nutritional habits may translate to poor nutritional outcomes for U5s. The reduced odds of U5M in households with over seven members mirrored the findings of some researchers [51, 52] but contradicted those of others [53, 54, 55]. This finding could be because the SSGZ like most African communities is communal in nature, and childcare is seen as a community responsibility thus large family sizes are a source of sustenance, knowledge, care, and supervision [56, 57].
The increased odds of U5M among males were similar to the findings of other researchers [20, 26, 17]. This may be attributed to the effects of genetics which result in delayed foetal lung maturation in boys increasing the incidence of respiratory illness and the inhibitory effect of the male hormones on the immune system [58]. Furthermore, the association of U5M with high birth order and short birth interval found in this study is consistent with the findings of past literature [20, 32, 19], and may be explained by maternal reproductive health, parent-child behaviour, and sibling relationships. Women require time to recover after childbirth, however, short intervals between successive pregnancies may result in poor uterine healing, anaemia, and cervical insufficiency hampering the ability to sustain foetal growth increasing the risk for preterm births, foetal malnutrition, infection, and death [59, 60]. A short birth interval may also indicate that a mother does not breastfeed extensively depriving her children of the nutritional and immunological benefits of breastmilk. There may be fewer maternal and household resources available for each successive pregnancy, and higher-order pregnancies are more likely to be unintended conceptions and are linked to a late start of antenatal care and vaccinations [61]. Also, a higher number of older siblings increases the exposure of U5s to communicable infections and developmentally inappropriate activities [62, 63].
The increased odds of mortality for U5s who were smaller at birth were similar to the findings of available literature [25, 26, 31;20; 64]. However, of the factors identified in this study, low birth size alone accounted for over 47% of the U5M risks. Children born with a low birth weight are at a higher risk of morbidity and mortality due to malnutrition, susceptibility to infections, respiratory distress, birth trauma, growth failure, developmental delay, and the development of chronic non-communicable diseases [65; 66]. The reduced odds of U5M in households with two U5s supports the findings of previous studies [24, 40]. Mothers of other U5s might have learned and experienced parenting through time, which could account for the protective effect of this characteristic on child survival, or the presence of multiple mothers with U5s in the same household gives these mothers the chance to support and learn from one another's experiences, as well as share health resources and information.
The results of the PAR% for children born to overweight mothers indicate a change of overweight BMI to within the optimal range would eliminate about 8% of U5M among children born to this group of mothers, while 47.12% (95% CI 37.77% -59.47%) of U5 deaths could be prevented if interventions could prevent small birth size. However, a 19.40% (15.68%-23.12%) reduction in U5M is attributed to having two U5s within a household, but not all these characteristics are amenable to public health interventions.
Strengths and Limitations
To our knowledge, this is the only study on U5M focused on the SSGZ of Nigeria which also provides information on PAR thus providing data relevant to this region. It also used a pooled dataset, and categories increasing its statistical power and made it possible to detect significant associations. However, the quality of the findings may have been undermined because of the retrospective nature of the information collected by the NDHS, also, the unknown confounding effect of variables not considered cannot be accounted for.