The global population is projected to reach 9.71 and 10.35 billion by 2050 and 2100, respectively. Africa will account for 105% of the projected total increase in global population between 2022 and 2100. Its population will increase from 1.36 billion in 2020 to 3.92 billion by 2100. This rapid growth, over a relatively short period, together with the compositional effects it will engender, will have significant implications for development prospects in the region (1). Recognizing this reality, African Heads of State and Government devoted the year 2017 to “Harnessing the Demographic Dividend through Investments in Youth” (2), as a critical pathway to realizing the continent's aspiration for economic transformation. Yet, concrete action in realizing this strong political moment has remained muted. Ninety-one percent (91%) of this projected growth in Africa's population will be in sub-Saharan Africa (SSA).

The population growth of SSA is driven largely by high fertility and child onset of childbearing (3, 4). Apart from having more children on average than women in other regions, women in SSA generally start childbearing earlier and have very high levels of adolescent childbearing, high desired family size, and low levels of use of modern contraceptives (3–5). Highest rates of child marriage occur in sub-Saharan Africa and as high as 40% of women Western and Central Africa got married before the age of 18 (6).

Child marriage is the consequences of factors at such as low level of literacy of the girls and her parents, economic problems, gender norms and gender-based violence. Child marriage is one of the indicators of gender inequality and is an impediment against the full participation of girls in education and labor force (7). Child marriage and teen pregnancy remain obstacles against completion of secondary education and beyond. On the other hand, female education is a key predictor of fertility, especially secondary education and higher (8). Secondary and higher education may increase women's opportunities for work outside the home, their ability to contribute to decision making with their partners, and greater agency in taking action that advances their personal well-being and managing their family size (8–10). It is also beneficial in tackling the negative economic impacts of child marriage (11) and contributes to the achievement of the sustainable development goals (SDG 5) (12). More importantly, better educated women are more likely to prioritize the education of their children thereby creating inter-generational benefits (8).

Early marriage is often associated with increased risk of teen pregnancy. Teen pregnancy also increases the risk of deadly health consequences such as eclampsia, puerperal endometritis, low birth weight, preterm birth, and other complications (13). The World Health Organization recommends that marriage before the age 18 and pregnancy before the age of 20 should be reduced (14).

Targeting adolescent girls with programs that reduce the onset of pregnancies will achieve multiple development outcomes and contribute significantly to reducing fertility and population growth rate—in addition to its value to the girls, their families, communities, and society. First, there is a strong positive association between female education and onset of marriage and childbearing, fertility levels, fertility desires, independent fertility decisions (including use of contraception), and access to employment opportunities outside the home. More importantly, starting childbearing later increases the age gap between mothers and their daughters (intergenerational gap), which is seen as the second most important determinant of population growth, after fertility (number of children) (15).

Although there is emerging evidence from low- and middle-income countries that programs targeting adolescent girls with long-term follow up are likely to be effective and sustainable, there is limited evidence on what specific interventions or which aspects of complex intervention designs are effective in reducing child marriage and teen pregnancy (16).

Implementing evidence-based interventions that reduce teen pregnancies and child marriage is critical not only for the future development of the society, but also for the entire life and wellbeing of adolescents. It is, therefore, essential to synthesize the available evidence to guide future research and intervention focus. Our preliminary search found no recent systematic review that reported the effectiveness of interventions on teen pregnancy and child marriage in sub-Saharan Africa. Cognizant of this, this systematic review was aimed to identify and synthesize evidence on the effect of interventions that have been implemented to reduce teen pregnancy, and child marriage in sub-Saharan Africa.

This systematic review was conducted using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (17). We conducted the review based on an a-priori protocol (Registry number CRD42022327397) (18).

Initial search yielded 1,664 articles. After removing duplicates 1,323 articles were left for screening by title and abstract, out of which 317 articles were left for full text reading. Finally, 30 articles were included. Detailed information was sought from the articles having different versions of the reports. Some of these studies had long report versions and short published versions published in peer reviewed journal articles. Even though information from the seven redundant articles was included to enrich the original studies, these redundant articles were not counted as separate studies. Hence, the records were considered as 30 articles (Figure 1). On the other hand, reports from the same trial were treated separately if they reported on different outcomes or if they addressed different data points.

The studies whose reports were merged include Baird 2009 (23), Baird 2010 (24) and Baird 2011 (25); Baird 2015 (26) and Baird 2016 (27); Duflo 2014 (28) and Duflo 2015 (29), Bandiera 2012 (30), Bandiera 2015 (31), Bandiera 2017 (32), Bandiera 2018 (33) and Bandiera 2020 (34); Dupas 2009 (35) and Dupas 2011 (36). On the other hand, four studies conducted in Zimbabwe (37, 38)) and Ghana (39, 40) that reported data at different time points from the same trial were reported separately.

The interventions reported in the included papers are broadly classified into one the following categories based on the areas they addressed (health, education, wealth, or community dialogue). a.

Interventions aimed to build educational assets (E),

Out of the studies that comprised four component intervention, three of them reported on marriage outcomes. These projects were conducted in Kenya (46), Ethiopia (45) and Zambia (47). Surprisingly, the effect of these comprehensive interventions comprising violence prevention, heath, education, and wealth components, was not significant when compared to single component intervention (violence prevention) alone. An arm with four component interventions (health, education, wealth, and violence prevention) was not significantly different from an arm with single intervention (violence prevention alone). On the other hand, subgroup analysis indicates that the four-component intervention (intervention with health, education, wealth, and violence prevention) significantly reduced child marriage among baseline out-of-schoolgirls when compared to an arm with violence prevention alone.

Similarly, study conducted in Zambia reported on intervention that comprised health, education and wealth components and community dialogue to change norms around child marriage. The study reported that incidence of marriage before the age of 18 was 21% lower among the arm exposed to combinations of intervention that comprised economic support for families and tuition and material support for girls, and sexual and reproductive health education when compared to the control arm with no intervention. This change was not statistically significant (47).

An Ethiopian study that examined the effect of combined economic intervention, information and community dialogue to change norms around child marriage reported significant effect of the intervention on child marriage among girls aged 8–17 years old (45). B.

Programs/Projects that addressed three components

On the other hand, combined interventions comprising school promotion, asset transfer and community dialogue were effective among younger adolescents (less than 14 years of age) in Tanzania (43) and in Ethiopia (44). However, in Ethiopia, there was reverse effect among girls aged 15–19 years. Girls in treatment arm had 2.4 times higher likelihood of getting married compared to those girls in the control arm (44).

Tanzanian study reported that girls in an arm with four component interventions comprising “Cash PLUS” interventions (cash transfer plus livelihoods and life skills training, mentoring and an asset transfer, combined with linkages to strengthened government-run HIV and SRH services), were less likely to enter into marriage compared to the girls in the “Cash ONLY” arm (arm that received the cash transfer program alone) (48). The cash transfer involved both unconditional (to reduce vulnerability and increase income) and conditional (up on school enrolment or seeking essential health services). C.

Programs/Projects that comprised two components

For instance, a four year follow up study conducted in Uganda reported a significant effect of empowerment and livelihood and life skills training and provision of reproductive health (RH) information (8 pp lower) compared to control communities that did not receive any of the interventions (34). A Kenyan study found that violence prevention combined with education promotion was more effective (with 6.2 pp less) when compared to violence prevention alone in reducing child marriage among out of school adolescent girls even though the effect was not significant for school adolescent girls (46). In Kenya, even though education subsidies were effective when implemented alone, they were not effective when combined with national HIV/AIDS curriculum which focuses on abstinence only. In addition, education subsidies when combined with an add on HIV education, and information on condom were not effective in reducing teen pregnancy (29).

Study conducted in Zambia reported that multicomponent intervention comprising health/social and wealth components (the provision of safe spaces for adolescents combined with heath vouchers and saving accounts) did not have any impact on child marriage when compared to control arm (no intervention) (49).

Study conducted in Zambia reported that intervention that comprised education and wealth components (financial support to families and girls, tuition, and material support) reduced incidence of marriage before the age of 18 by 14% when compared to the control arm with no intervention. This difference was not statistically significant (47).

Study conducted in Ethiopia that examined the effect of information and community dialogue to change norms around child marriage reported significant effect of the intervention on child marriage among girls aged 8–17 years old. In the study, the community dialogue was complemented by the information provided at school clubs on family planning and sexual and reproductive health issues. The approach of community mobilization consisted of training influential community members such as religious leaders, teachers, gender activists, community leaders. These influential community members would then facilitate community conversations to reflect on challenges that girls face when entering marriage and elicit empathy and dispel myths around child marriage (45). D.

Projects with one component interventions

Particularly impressive result reported from studies under this category is one Ghanaian study with relatively longer duration of follow up (39). The study reported significant impact of providing scholarship on reducing the probability of ever getting married or living with partners across years of follow up (39, 40). A multicounty study conducted in Burkina Faso and Tanzania reported that community dialogue alone was effective in reducing child marriage in Burkina Faso [girls in community dialogue arm aged 15–17 years had two-thirds less risk (RR = 0.33; 95% CI, 0.19, 0.60) of being married]. The same study reported that the community dialogue does not have significant effect on child marriage on both girls aged 12–14 years and 15–17 years old in Tanzania (43). The difference in the effectiveness of the intervention in the two countries may related to the intensity and the approaches of the interventions. The approach utilized in Burkina Faso was recruiting and training community members and training them for five days so that they will mobilize and group the community into groups of 30 people. The groups were provided 16 sessions of training on negative impacts of child marriage and the value of girls' education, after which they will devise and implement solutions. Some of the devised strategies include house-to-house campaigns and rewards or punishments to the community members. On the other hand, in Tanzania the approach included recruiting religious leaders and training them for two days on benefits of girls “education and benefits of delaying child marriage. The leaders were also trained on how to facilitate discussions and deliver messages letting them deliver messages on routine community meetings such as religious meetings. In addition, in Tanzania, there was no system for sustained contact system to trace the work of the community leaders. The community leaders were not expected to report the community members whom they contacted (43).

Study conducted in Zimbabwe demonstrated that supporting orphans and vulnerable adolescents to remain in school reduced child marriage both in the short term (2 years) (37) and long-term (5 years) follow up (38). The school support covered tuition fees, uniforms, school supplies and assigning helper to monitor participants' school attendance.

Study conducted in Malawi reported that there is no significant effect of conditional cash transfer (CCT) on marriage among schoolgirls both in short-term (2 years follow up) and long-term (5 years) follow up. The same study reported statistically significant effect of conditional cash transfer (CCT) among out-of-school girls both in short-term and long-term evaluation. The study also reported that UCCT was effective on baseline schoolgirls during and immediately upon completion, but not in the long-term (after 5 years) (27).

Using data from a four-year follow up study, a Kenyan study reported that UCCT provided to orphan and vulnerable children has no significant impact on child marriage (50). Similarly, a Malawian study reported that unconditional Cash transfer (UCCT) to ultra-poor rural households has no significant impact on child marriage (52). Other multi-country study also reported that unconditional Cash transfer (UCCT) to ultra-poor rural households did not significantly reduce child marriage both in Malawi and Zambia (51).

Study from Zambia reported that the provision of safe spaces for adolescents when provided alone or when combined with heath vouchers did not have any impact on child marriage when compared to control arm (no intervention) (49).

The categories of interventions whose effect on teen pregnancy was reported using categories just like that of child marriage described above. A.

Programs/Projects that addressed four components (Health, Education, Wealth, and community dialogue)

Three studies reported on interventions that addressed three component interventions that addressed any combinations of health, wealth, education, and violence prevention. These projects were conducted Kenya (42, 46) and Tanzania (48). The two Kenyan studies conducted both in slum (42) and pastoral (46) settings reported that effect of these multiple component interventions comprising violence prevention, education and health was not significantly different from that of standalone (violence prevention) intervention. Similarly, a Tanzanian study reported there was no significant difference in the rates of teen pregnancy among girls in an arm with multicomponent interventions compared to those girls in the “cash only” arm (arm that received the cash transfer program alone) (48). The multicomponent interventions comprised cash transfer conditioned up on school enrolment or seeking essential health services and unconditional cash transfer plus livelihoods and life skills training, mentoring and an asset transfer, combined with linkages to strengthened government-run HIV and SRH services). C.

Programs/Projects that addressed two components

A Kenyan study conducted in pastoral setting found that violence prevention combined with education promotion reduced teen pregnancy by one third (marginally significant); on the other hand, the effect was statistically significant for out of schoolgirls (46). Study in the same country found no significant effect of violence prevention combined with education promotion on teen pregnancy in urban informal settlement setting (42). Another Kenyan study reported that education subsidies are not effective in reducing teen pregnancy when combined with national HIV/AIDS curriculum which focuses on abstinence only messages. In addition, education subsidies when combined with an add on HIV education, and information on condom were not effective in reducing teen pregnancy (29). A Zimbabwean study conducted among urban out-of-school youth reported that combining livelihood intervention (vocational training and micro-grants) with life-skills and health education had only marginal effect on teen pregnancy when compared to life-skills and health education [HR 0.61, 95% CI, (0.37, 1.01)] (41).

Study from Zambia reported that intervention with health/social and wealth components was not effective. The study found that the provision of safe spaces for adolescents when combined with heath vouchers and heath saving accounts did not have any impact on teen pregnancy when compared to control arm (no intervention) (49). D.

Projects with one component interventions

Like in the case of child marriage, the study conducted in Ghana reported significant impact of provision of scholarship in reducing the probability of ever getting pregnant consistently across years (39, 40). Study conducted in Zimbabwe demonstrated that supporting orphans and vulnerable adolescents via School subsidies (fees, uniforms and supplies) reduced teen pregnancy both in the short term (2 years) (37) and long-term (5 years) follow ups (38). Study conducted in Malawi reported that there is no significant effect of conditional cash transfer (CCT) on marriage among schoolgirls both in short-term (2 years follow up) and long-term (5 years) follow up. The same study reported statistically significant effect of conditional cash transfer (CCT) among drop-out girls both in short-term and long-term evaluation. The study also reported that UCCT was effective on baseline schoolgirls during and immediately upon completion, but not in the long-term (after 5 years) (27).

Using data from a four-year follow up study, a Kenyan study reported that UCCT to orphan and vulnerable children significantly reduced the risk of teen pregnancy (50). On the other hand, a Malawian study reported that unconditional Cash transfer (UCCT) to ultra-poor rural households has no significant impact on teen pregnancy (52). Other multi-country study also reported that unconditional Cash transfer (UCCT) to ultra-poor rural households did not significantly reduce the risk of teen pregnancy both in Malawi and Zambia (51).

From HIV prevention projects, national HIV/AIDS curriculum that focuses on abstinence only was not effective. On the other hand, HIV prevention messages were effective in reducing teen pregnancy (29). Communicating HIV risk based on age and sex profile reduced teen pregnancy by 27.7% (p < 0.05). Communicating the risk averts 29.4 pregnancies by older partners. Communicating HIV risk information decreased the incidence of cross-generational pregnancies by 61.7% (relative to the comparison) (35, 36). On the other hand, a study conducted in Zimbabwe reported that community-based multi-component HIV prevention intervention does not have significant effect on teen pregnancy (56).

While school sexual and reproductive health education did not have significant impact on teen pregnancy in Tanzania (55), intensifying adolescent sexual and reproductive health services reduced teen pregnancy in Uganda (54). Another intervention with important consideration was text messaging of reproductive health information. A Ghanaian study reported that both unidirectional [odds ratio (OR) = 0.14; 95% CI = 0.03, 0.71] and interactive messages containing reproductive health information (OR = 0.15; 95% CI = 0.03, 0.86) lowered odds of self-reported pregnancy for sexually active participants (at 15 months follow up) (57).

The other important interventions under this category are creating safe spaces for adolescents. Study from Zambia reported that the provision of safe spaces for adolescents when provided alone or when combined with heath vouchers did not have any impact on teen pregnancy when compared to control arm (no intervention) (49).

This review attempted to search and locate the current available evidence on the effectiveness of interventions that have been implemented to reduce teen pregnancy and child marriage in sub-Saharan Africa. The interventions reported in the review were generally categorized into (a) Interventions aimed to build educational assets (E), (b) Interventions aimed to build life skills and health assets (H), (c) Interventions aimed to build livelihood and/or financial skills [Wealth building interventions (W)], (d) Interventions designed to change community norms [including violence prevention, women and girls' empowerment and/or prevention of early marriage (C) and e] Combination of one or more of the above.

Even though the amount of investment in multi-component interventions is remarkable, their (additional) effect on child marriage and teen pregnancy is not significant. For instance, multicomponent interventions comprising as many as four domains of interventions were not effective. This might have been because of the lack of focus or logistical difficulties related the implementation. The other inherent problem of studies with multiple domains of interventions is that they had multiple outcomes and they were not powered enough to detect differences in child marriage or teen pregnancy. Besides that, some lacked adequate balance at baseline. In addition, adolescent-based interventions were only subcomponents of the bigger development packages (48). The strength of such interventions, on the other hand, is that they have collected data on several health and economic variables, and it is clear to understand the modifying effect of several variables and the overall fit of the interventions within the educational, social, economic and health systems of the population. In addition, it will provide an opportunity for understanding the pathways through which the intervention affects the outcomes (child marriage and teen pregnancy). For instance, unconditional cash transfer (UCCT) (50) was effective in reducing teen pregnancy but not on reducing child marriage. From its effect on schooling, it was possible to hypothesize that the intervention reduced teen pregnancy rate not by delaying marriage, but by keeping adolescent girls in schools. Findings of the study conducted in Malawi also suggests that unconditional cash transfer programs implemented among in-school girls were only effective in the short-term (while the program was in place) (58). This may be due the fact that girls may not build assets using the short-term funding from the UCCT. On the other hand, the conditional cash transfer (CCT) was effective among out-of-school girls both in short-term and long-term follow ups and it was not effective both in short-term and long-term among in-school girls (58).

Even though it is difficult to conclude, it appears that interventions with fewer domains were promisingly effective. For instance, interventions such as education subsidies were effective when implemented alone and not effective when combined with other interventions, such as the national HIV curriculum which focuses on abstinence only prevention messages (29). School promotion interventions were effective in reducing both teen pregnancy and child marriage (29, 37–39). Particularly, study conducted in Ghana, which had a follow up period of 12 years demonstrated that provision of scholarship that covers secondary school tuition and exam fees significantly reduces marriage and pregnancy (39). Previous observational study reporting on multi-country data has also reported the effectiveness of eliminating primary school education fees in reducing child marriage (59). This underscores that addressing barriers to attending secondary school is critical not only in keeping adolescents in school but also in helping them to be empowered and delay their start of childbearing. This is in line with the findings that indicate life skills and livelihood training and mentoring interventions are effective in reducing child marriage (34, 48).

Examining the population subgroup indicates that some of the interventions were effective only among out-of-school adolescent girls, while their effect among in-school adolescent girls were not significant. For instance, study conducted in Kenya reported that the effect of the multicomponent interventions was greater among girls not in school at baseline. For instance, the intervention comprising violence prevention, education, health and wealth (VEHW) components significantly reduced child marriage compared to the control arm (violence prevention alone) among girls not in school at baseline. On the other hand, the effect was not statistically significant among the full sample (46). In addition, study conducted in Malawi found that conditional cash transfer (CCT) programs were effective both in short term and long term follow ups among out-of-school girls, but not among in-schoolgirls (58). While the mechanism is still not clear, some suggest that this may be through increasing educational outcomes (Kangwann 2022) and through tackling cost related barriers, especially among the neediest segments of the population, such as orphans (Hallfors 2015). This especially holds true for girls who could not continue schooling because of financial barriers and potentially financial barriers are really forcing girls to enter marriage early. On the other hand, some interventions, such as community dialogue were effective in reducing child marriage without impacting educational outcomes (Chow 2021). Clarifying such controversies with strong study designs might help in understanding pathways on how the interventions work.

Though routine adolescent sexual and reproductive health services were not effective (55), intensifying Youth Friendly Services (YFS) through youth corners, outreach, social and behavior change communication intervention (SBCC), counseling, family planning (60), was effective in reducing teen pregnancy. In addition, text-messages containing reproductive health information were effective (57). This is promising result as expansion of mobile technologies are increasing.

The other intervention that is promising, if implemented systematically, is community dialogue (43, 45). However, for community dialogues to be effective, there should be intensive training for the facilitators and appropriate sustainable strategy to trace the activities of community leaders. For instance, the community dialogue in Burkina Faso that used intensive training and sustained reporting and tracing mechanism was successful. On the other hand, community dialogue in Tanzania that was intense and that lacked sustained contact system was not effective (43). In addition, community dialogue has been implemented as part of other interventions (43, 45, 47). Especially, when implemented along with other interventions that are delivered through school clubs, it will increase the effect of the intervention by letting adolescent girls get adequate information to backlash misperceptions or negative interactions from the community potentially resulting from exposure to low intensity or inadequate exposure to community conversations about reducing child marriage (45).

While interpreting the effectiveness of the interventions, it is critical to take the local context into account. For instance, local security situations affect not only the effect of the interventions but also the fidelity of the interventions and the intervention uptakes. In addition, factors associated with instability (61) and migration (43) also challenge progress in the evidence base to the reduction of teen pregnancy and child marriage particularly among more vulnerable population groups in rural settings. The other critical thing that should be considered is that the effect of some interventions may cease if there is no means to accommodate their running costs and sustain them, such as the cash transfer programs (58). This implies that any innovative intervention should be sustainable, economically and politically. There is room for innovation on what might work to reduce child marriage and teen pregnancy in Sub-Saharan Africa where child marriage has remained high. In addition, because of the high demand for such interventions in fragile and humanitarian contexts, there should be an innovative mechanism to design context-specific interventions and strategies for follow up. Even though there are few studies among refugees, some were not powered for the outcome, and/or they did not include child marriage as primary outcomes (62, 63).

The current review has attempted to look broadly at evidence regarding effective interventions in reducing child marriage and teen pregnancy in sub-Saharan Africa. The review was comprehensive in addressing both published and unpublished articles. However, it is important to acknowledge certain limitations of the review. First, the review did not address studies reported in languages other than English. This is particularly a significant limitation given that Central and West Africa, which are largely Francophone, have some of the highest fertility and lowest contraceptive use levels in Africa and may have attracted interventions with fertility-related outcomes that are not published in English.

The review underscores the need for high quality research to guide program and policy options in achieving demographic transition in Africa. As described earlier, some interventions did not have adequate follow up period and their long-term effects were not investigated. Therefore, more evidence is needed to inform the design of interventions with potential to impact fertility-related outcomes in SSA.

While the findings of the review should be interpreted in the light of the above limitations, the evidence generated from the review provides clear guidance for understanding current gaps and for designing programs and policies with the potential to affect child marriage and teen pregnancy in sub-Saharan Africa.