Levels and trends in fertility rates among adolescents aged 10–14 and 15–19 in 201 countries and areas from 1950 to 2023

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Background: Reducing adolescent childbearing and addressing the multiple factors underlying it are essential for improving sexual and reproductive health and the social and economic well-being of adolescents. Very early childbearing increases maternal and neonatal health risks and perpetuates educational and economic disparities. Adolescent birth rate (aged 10–14 years; aged 15–19 years) is an indicator to monitor progress towards Sustainable Development Goal (SDG) Target 3·7, by 2030, ensure universal access to sexual and reproductive health-care services, including for family planning, information and education, and the integration of reproductive health into national strategies and programmes. However, the availability and reliability of data on adolescent fertility rates is low. Methods: We compiled a database with 36,682 observations from 236 countries and territories, integrating data from vital registration systems, sample registration systems, household surveys, and population censuses. We adjusted the incompleteness of birth registration and accounted for recall biases in birth histories recorded in surveys and censuses. Bayesian models estimated ASFR for ages 10–14 and 15–19, using covariates such as total fertility rates (TFR) and female educational attainment and adjusting for biases and underreporting. We calculate the number of births to adolescents by applying rates to the female population in the respective age groups. We present comprehensive annual estimates of age-specific fertility rates (ASFR) for girls aged 10–14 and 15–19 from 1950 to 2023 for the world, regions, and 201 countries and territories with a total population of at least 90,000 inhabitants as of mid-2024. Model performance was validated using out-of-sample testing. Findings: Between 1990 and 2023, global ASFR for girls aged 10–14 decreased by 76%, from 4·5 [4·1; 5·2] to 1·1 [0·9; 1·4] births per 1,000, while ASFR for girls aged 15–19 fell by 48%, from 74·7 [72·5; 77·1] to 39·0 [36·8; 41·4] births per 1,000. Central and Southern Asia achieved the largest relative reductions (95% for ages 10–14; 80% for ages 15–19). Sub-Saharan Africa, with smaller relative decreases (76% for ages 10–14; 32% for ages 15–19), remains the region with the highest ASFR in 2023 at 3·2 [2·5; 4·2] per 1,000 for ages 10–14 and at 94·4 [86·3; 103·4] per 1,000 for ages 15–19. At the country level, the birth rates for girls under 15 decreased by at least two-thirds in 115 [102; 122] countries and for the age group 15–19 in 72 [67; 79] countries between 1990 and 2023. In 2023, births to mothers aged 10–14 years were estimated at 347 [285; 454] thousand, a decline from 1·15 [1·05; 1·34] million in 1990, and for those aged 15–19 years at 12·2 [11·5; 12·9] million, a decline from 18·9 [18·4; 19·5] million in 1990. The number of births among adolescents aged 15–19 in Sub-Saharan Africa increased from 3·6 [3·6; 3·7] million in 1990 to 6·2 [5·6; 6·7] million in 2023 due to population growth and slower fertility declines, representing increasing proportion of global births from 19·2% [18·5%; 19·9%] in 1990 to 50·6% [47·7%; 53·5%] in 2023. Interpretation: Despite significant global progress in reducing adolescent fertility, regional and national disparities persist, with high adolescent birth rates in many countries of Sub-Saharan Africa, Oceania and Latin America and the Caribbean. Targeted interventions addressing child marriage, educational inequities and lack of access to reproductive health servic