This analysis suggests limited and patchy progress has been made in reducing adolescent first births in sub-Saharan Africa over the last two decades. Eastern and Southern Africa has shown slightly faster progress in reducing adolescent pregnancy in the short term, but the situation is reversed for Western and Middle Africa, and there is no evidence of widespread accelerated progress in more recent years. In many countries a large proportion of women have their first baby before the age of 20 years, and in many countries, particularly in Western/Middle Africa a notable proportion of this group have given birth before the age of 16 years. However, within regions there is considerable heterogeneity (although very few countries have made marked progress in reducing adolescent first births over the time period studied).
Heterogeneity of progress in reducing adolescent first births is somewhat difficult to explain. Levels of adolescent motherhood are associated with marriage, female education and economic progress, as well as cultural factors and access to family planning, but these factors are often complex and inter-related. While early marriage is declining somewhat in sub-Saharan Africa, it remains prevalent in many countries and progress is inconsistent [16], which may partially explain persisting high levels of adolescent first births. Level of education is recognised as an important determinant [17], but the relationship at national level between educational attainment and adolescent pregnancy is not straightforward. While access to primary education for girls has increased markedly in most countries within sub-Saharan Africa over the last three decades [18], this is often not reflected in positive changes in adolescent first births, which may reflect the persistence of poor access to secondary schooling. Further research is needed to analyse more precisely the relationship between education and adolescent motherhood in terms of level and quality of schooling, as well as how this is affected by other socio-economic and cultural factors, and health care availability.
It might have been hoped that even if the reduction in adolescent first births has not been marked, the proportion occurring among the youngest, most vulnerable group would have reduced. However, in many countries our analysis suggests the opposite. The marked rise in very early adolescent births seen in Mali, Chad and Benin are particularly concerning, and the fact that these increases have occurred during a period of modest decline in other age groups suggests different pathways and drivers. The fact that in the Western/Middle Africa region the proportion of first births < 20 years occurring in girls under 16 years has actually increased is also concerning, and points to the need for further study on the underlying specific factors for this age group. It is also worth noting that in many countries reductions in marriage for those under 15 years has been differentially poor compared to reductions for women aged 15–17 years [16]. These very young adolescents are disadvantaged on a number of levels. There is evidence that adolescent mothers under the age of 16 years suffer from greater health risks to both themselves and their babies than older adolescents [5, 19,20,21,22]. In addition, the < 16 years group are particularly concentrated amongst the poorest and rural residents, who have less access to reproductive and sexual health information and services. It is vital that programmes aimed at reducing adolescent pregnancy focus on these younger adolescents, who may be restricted from accessing other initiatives or services due to cognitive, financial or logistic limitations. Research on what approaches are most successful for this age group is limited, but studies suggest a more holistic approach focused on individual and social assets may be more appropriate [23]. It is also important to note that among this younger age group sex is more likely to be coerced, highlighting the important links between sexual health and child protection for this vulnerable group [24].
Rising levels of very early adolescent motherhood (< 16 years) in Chad, Mali and Niger could partly be explained by the presence of armed conflict and instability during the period. Findings from a recent systematic review suggested that the increase in early marriage and subsequent childbearing that may occur as a result of armed conflict may be particularly focussed amongst the youngest adolescents [25] and indeed there is evidence that there has been an increase in marriage in very young adolescents in Mali within conflict-affected communities [26]. This often reflects the desire for families to “protect” their daughters from risk of sexual violence or perceived threats to moral welfare resulting from the collapse of community and social structure and mores, or from financial considerations [27]. In these countries the vast majority of women who give birth before 16 years are married at the time of birth so this trend may well follow increases in early marriage. However, Benin has been relatively politically stable in the last few decades. In this context, there is strong evidence of a high risk of sexual assault and violence against adolescent girls, particularly in the school environment, which may be partially driving these figures [28]. Further studies are needed to better understand the context of very early adolescent pregnancy in countries where it is increasing.
Our findings also clearly point to sharp socioeconomic and urban / rural inequities in adolescent first births, which appear to be increasing over time. This apparent concentration of adolescent births among the poorest and those in rural areas has important implications for the SDG commitment to “leave no-one behind” and highlights the need for nuanced indicators that capture these increasing inequalities. Evidence of growing inequity has important implications for programme development, as the poorest and those in rural areas are often inadequately served by large-scale programmes to improve adolescent access to contraception, as for instance they may be out of school or less able to access media-based campaigns [29]. More broadly, adolescents face significant barriers to SRH services, and in particular unmarried adolescents experience stigma and discrimination from both communities and health care providers [30]. Efforts to promote an enabling environment that supports adolescent SRH and rights are likely to require widespread changes and interventions [31] However, it must also be recognised that poverty, lack of education and the normalization of sexual abuse underpin inequities in adolescent childbearing [29]. The concentration of births within the youngest age groups in the poorest quintile points to a compounding of vulnerability. Given this, multisectoral approaches that address these structural drivers are key.
This paper has a number of limitations, which should be highlighted. Firstly it relies on recall data from survey respondents, and there is strong evidence that the reporting of sexual and reproductive health events may be prone to both intentional and unintentional bias [15, 32, 33]. Some studies indicate a tendency for very young adolescents to overstate their age at time of survey (and therefore overstate their age at first birth), and this risk has been reduced by using the 20–24 year cohort.
Further issues are that measures of wealth and place of residence are taken at time of survey rather than at the time of adolescent birth. Therefore it is impossible to clearly state whether these factors are determinants of adolescent birth, or outcomes: for instance adolescent motherhood may result in poor long term socio-economic prospects or migration. Longitudinal studies are needed to examine these issues more thoroughly. Sample sizes for some countries, particularly for the disaggregated groups, may also be relatively small, leading to large confidence intervals which means findings should be interpreted with some caution (see Additional files 2 and 3). In addition, we do not calculate and analyse wealth quintiles separately by urban and rural residence: the majority of those in the lowest quintiles will be rural, and it is not possible to identify whether there is poor progress among the urban poor. Further work is currently ongoing to explore this issue.
The heterogeneity of progress within the geographic groups points to the value of using aggregate data with caution. Further research is needed to consider what characteristics underpin the different patterns of adolescent motherhood, and whether a more useful typology can be developed that group countries in a manner that aids understanding of how best intervention programmes can respond. Careful analysis at the individual country level is also vital in understanding trends and patterns specific to that context.
