Introduction
Every year, nearly 12 million adolescent girls and young women aged 15–19 years and nearly a million under 15 years give birth.1 The majority of these births are in low-income and middle-income countries (LMICs).2 The adolescent fertility rate (birth rate per 1000 girls and young women aged 15–19 years) over the period 2015–2020 was the highest in the sub-Saharan Africa (SSA) region at 102.8 births per 1000 person-years, far higher than the global average (44 per 1000), followed by South Asia with 26 births per 1000 girls aged 15–19.3
Adolescence is a unique stage of human development and an important time for building the foundation of good health; consequently, pregnancy during this lifestage can have impacts on both a young woman and her children. Early pregnancy can lead to devastating health consequences for the mother, since adolescent girls may not yet be physically and biologically ready for pregnancy or childbirth.3 Many adolescents experience complications during pregnancy and childbirth, which has become the leading global cause of death among 15–19-year-old females.4 Pregnant adolescents are at a higher risk of receiving inadequate antenatal care (ANC) in some settings.5 A significant proportion of adolescents in SSA do not access nor utilise maternal services during pregnancy, which is a consequence of several individual, interpersonal, institutional and systemic factors.6 Early pregnancy and motherhood for an adolescent girl in some contexts can also have adverse social consequences such as stigma and dropping out of school.1 7 They may not have the opportunity to return to school which jeopardises their economic and employment opportunities due to their double burden of household maintenance and child-rearing,7 8 resulting in sustained poverty and increased vulnerability.
Reduction of adolescent pregnancy has long been the focus of several organisations and is of current policy interest. In fact, with only 8 years left to achieve the 2030 Agenda for Sustainable Development, agreed to by more than 190 countries, there remains a timely commitment and need to ensure access to sexual and reproductive healthcare services, particularly for adolescent girls and young women (Target 3.7), and eliminate child, early and forced marriage (Target 5.3), given their strong associations with adolescent pregnancy and its outcomes.9 Despite these efforts and the recent decline in overall adolescent mortality10 and global adolescent fertility rate, prevalence of adolescent pregnancies remains high and a major public health concern, especially in LMICs.
In standard surveys, reports and WHO statements, mothers under 20 are usually treated as a single group.11 However, adolescence represents a time of developmental transition, including physically, cognitively and psychologically, and there are substantial differences across the 10–19 years age range.12 Few studies have looked at the risk gradient versus age among young mothers. Several studies have associated early maternal age with neonatal and infant mortality,2 9 13 14 infant stunting and preterm birth even after adjustment for sociodemographic factors.15 In contrast, two recent multicountry studies did not find a consistent significant association between adolescent motherhood and stillbirth.16 17 Current findings and studies leave unanswered questions about the true nature of these relationships.
A meta-analysis of Demographic and Health Surveys (DHS) showed higher risk of mortality to neonates born to mothers aged <16 and 16–17 years old than neonates born to mothers aged 20–29 years in SSA and South and Southeast Asia,11 even after adjusting for socioeconomic, demographic and health service utilisation variables. In LMICs, the infant mortality rate was higher among mothers with ages of 12–14 and 15–17 years than among older mothers.13 Finlay et al14 showed in a separate analysis that the risk of infant mortality in SSA is highest for high parity young mothers, and short birth intervals negatively affect infant mortality and stunting outcomes. A WHO multicountry study divided mother ages into <16, 16–17, 18–19 and 20–24 years old. They found stillbirth rates among adolescent mothers to be mildly higher than 20–24 years old mothers (ORs 1.0–1.3), with the difference significant only for the 16–17 years old group.17 A more recent study examined the association between maternal age, both young and advanced and risk of neonatal mortality in LMICs using DHS data, and found the risk of mortality of neonates born to mothers aged 12–15 and 45+ years was higher than neonates born to mothers aged 25–29 years.18 A systematic review and meta-analysis in SSA found that most evidence about the effects of early childbearing was for mothers 15–19 years old as a single group, with very few studies providing data on adolescents aged <18, and concluded that there is a lack of high-quality observational studies that adjust for sociodemographic factors.19 Overall, there are limited number of studies focusing on risk gradient versus maternal age among young mothers, and majority of these studies focused on neonatal and infant mortality rather than broader child survival outcomes.
In our study, the most comprehensive of its kind to date, we have investigated the potential impacts of adolescent pregnancy on a substantially broader scope than previous studies, examining child mortality endpoints from stillbirths to under-5 mortality, and quantifying the risk gradient as a function of age from adolescence through young adulthood. In contrast to prior studies which focused mostly on survival endpoints around birth, we hypothesised that since adolescent mothers face greater physical, emotional and social challenges, the impact on their offspring’s survival might be felt throughout early childhood. In addition, to examine whether observed associations between maternal age and child survival may be caused by confounding variables that affect both, we explored adjustment for key demographic variables such as urban versus rural residence. We also investigated whether the association between mother’s age and child mortality endpoints might be mediated by maternal health-seeking. We focused on SSA, the region with the highest adolescent pregnancy and child mortality burdens, as well as South Asia, the second-highest region in child mortality burden where adolescent pregnancy rates fell rapidly in recent years. The comprehensiveness and multiregionality of our analysis helps frame the inconsistent findings from previous studies9 13–17 on the relationship between maternal age and child health outcomes. Disaggregation of the adolescent age group helps highlight the increased risk of younger adolescents and the potential benefits of providing health services for these girls.