The present study revealed substantial socioeconomic (wealth and education) and residence-based disparities in adolescent fertility, with higher inequalities observed among young women who resided in rural areas, those with low economic status, and those with no formal education. These disparities were observed in all the countries surveyed albeit at varying degrees, suggesting a persistent need for country-specific interventions to address the problem of high AFR in SSA.

Several previous studies reported a significant association between AFR and the dimensions of inequality including rural-urban residency, wealth, and education [30, 42,43,44]. In this study, we observed varied residence-based disparities in adolescent fertility, which skewed towards young women living in rural areas in all the countries surveyed except in Rwanda, where young women in urban areas had a marginally higher burden of adolescent fertility. This finding supports previous studies that have reported that adolescents who reside in rural areas have a higher fertility rate relative to those in urban areas [27, 44, 45]. In Ethiopia for instance, Alemayehu et al. [46] found that adolescents living in rural areas were four times more likely to have children than those in urban areas. The high fertility rate among adolescents in rural areas has been attributed to poverty and lack of educational opportunities [47], as well as limited access to sexual and reproductive health information and services [43]. Meanwhile, aside from having better access to contraceptives such as condoms, adolescents in urban areas are more exposed to social norms that discourage early marriages and childbirth, which contribute to their reduced fertility rate [42].

Remarkably, our observation in Rwanda supports earlier studies which reported that Rwanda has the lowest AFR in SSA [23, 43], with young women in urban areas having marginally higher rates of adolescent fertility [48]. The declining rate of adolescent fertility in Rwanda, particularly in rural areas, has been attributed to the persistent implementation of public interventions such as increased sex education, sexual and reproductive health promotion, and monitoring of girl-child education [48]. Other interventions include an enhanced legal framework to punish men who impregnate young girls [48], increased access to modern contraceptives, and improved family planning services [49]. Meanwhile, we observed that most of the countries with the greatest simple (Guinea, Niger, Nigeria, and Côte d’Ivoire), and complex (Niger, Guinea, Madagascar, Burkina Faso, Chad, and Nigeria) residence-based disparities in adolescent fertility were from West Africa. The high fertility rate among young women in West Africa was reported in previous studies [43, 45]. Thus, efforts to address the problem of high AFR in SSA must pay particular attention to countries in West Africa, especially among their rural population.

Similar to the findings from earlier studies [44, 50, 51], we observed varied wealth-based disparities in the rate of adolescent fertility, with lower rates observed among young women with the highest wealth quintile across all the countries surveyed. Both complex (PAR) and simple (D) inequality dimensions revealed that countries like Guinea, Nigeria, Madagascar, Cameroon, and Sao Tome and Principe ranked high in wealth-based disparities in adolescent fertility in SSA. Meanwhile, available evidence suggests that countries with increased wealth-based disparities have the highest AFR globally [3]. The increased rate of adolescent fertility among the poor has been attributed to their limited ability to access reproductive healthcare services including family planning [52], dropping out of school, increased exposure to early sexual debut [53], and increased societal pressure to get married and start childbearing [51, 54]. Thus, our findings affirm the need for persistent efforts to reduce poverty and close the income inequality gaps across the countries in SSA, particularly among those with high AFR.

Consistent with several previous studies [30, 44, 46], our findings revealed that wide disparities exist in adolescent fertility based on young women’s level of education, with lower burden observed among those with higher educational attainment. For instance, the complex (PAR) inequality measures suggest that in the absence of education-based disparities in the population, AFR would have reduced by 48.44%, 37.79%, 35.04%, 32.98%, and 32.67% in Chad, Mozambique, Mali, Angola, and Madagascar, respectively. Increased access to education reduces the risk of early sexual debut [53], early marriage and childbirth [54], and increased use of reproductive health services such as modern contraceptives [55, 56], which reduce AFR. Meanwhile, access to secondary or higher education remains poor in many countries in SSA although that of primary education has largely improved [57, 58]. For instance, Ilie and Ros [57] reported that the higher education net attendance rate in countries like Mozambique, Madagascar, and Mali is below 5%. Perhaps, increasing access to higher education and bridging the educational inequality gap could significantly reduce AFR in SSA, particularly in countries like Chad, Mozambique, Mali, Angola, and Madagascar.

Findings from this study suggest that the rate of adolescent fertility is disproportionately higher among women in rural areas, those with low economic status, and those with no or less formal education across the countries in SSA. Since the prevalence of adolescent fertility tends to be lower in countries with the lowest disparity in the dimensions of inequality [3], strategies aimed at reducing AFR in SSA could be targeted at bridging the inequality gaps in residence, wealth, and education across the countries. For example, increasing adolescents’ access to sexual and reproductive health information and services in rural areas, providing economic opportunities and financial support to less privileged adolescents, and implementing policies to improve female access to education and monitoring their educational progression could contribute towards reducing the burden of adolescent fertility among the disadvantaged population. Perhaps, such interventions could contribute toward the realization of the 2030 SDG agenda [59], and the United Nation’s global strategy for women’s, children’s, and adolescent health [60]. Also, because the present study provides multi-country data on inequality dimensions and the burden of adolescent fertility in SSA, it allows for a comparison of the disparities across the countries studied. Thus, our findings highlight the urgency for interventions to address the high rate of adolescent fertility, especially among countries like Guinea, Niger, Nigeria, Chad, Mali, Côte d’Ivoire, Madagascar, Burkina Faso, Madagascar, Cameroon, and Sao Tome and Principe. Besides, the multi-country analysis also provides data for progress monitoring in future studies.

In this study, we employed nationally representative datasets to provide insight into the socioeconomic and residence-based inequalities in adolescent fertility in SSA. As a result, our findings provide a foundation for tracking differences in the burden of AFR among sub-Saharan African countries using the WHO's HEAT software. Despite these strengths, the current study has drawbacks. First, the DHS datasets included in this study were done at different times in different countries. This may induce bias when comparing the extent of differences among countries in the dimensions of inequality and the rate of adolescent fertility. Aside from the varying survey dates, our study was based on a single survey year in each country. Hence, we were unable to conduct a trend analysis to ascertain the pattern of inequality characteristics in adolescent fertility across the countries over time. Finally, because both the inequality dimensions and the adolescent fertility were self-reported, they could be susceptible to recall and social desirability biases.