To investigate the risk of adverse pregnancy outcomes and caesarean section among adolescents in low- and middle-income countries.

Secondary analysis using facility-based cross-sectional data from the World Health Organization (WHO) Global Survey on Maternal and Perinatal Health.

Twenty-three countries in Africa, Latin America, and Asia.

Women admitted for delivery in 363 health facilities during 2-3 months between 2004 and 2008.

We constructed multilevel logistic regression models to estimate the effect of young maternal age on risks of adverse pregnancy outcomes.

Risk of adverse pregnancy outcomes among young mothers.

A total of 78 646 nulliparous mothers aged ≤24 years and their singleton infants were included in the analysis. Compared with mothers aged 20-24 years, adolescents aged 16-19 years had a significantly lower risk of caesarean section (adjusted OR 0.75, 95% CI 0.71-0.79). When the analysis was restricted to caesarean section indicated for presumed cephalopelvic disproportion, the risk of caesarean section was significantly higher among mothers aged ≤15 years (aOR 1.27, 95% CI 1.07-1.49) than among those aged 20-24 years. Higher risks of low birthweight and preterm birth were found among adolescents aged 16-19 years (aOR 1.10, 95% CI 1.03-1.17; aOR 1.16, 95% CI 1.09-1.23, respectively) and ≤15 years (aOR 1.33, 95% CI 1.14-1.54; aOR 1.56, 95% CI 1.35-1.80, respectively).

Adolescent girls experiencing pregnancy at a very young age (i.e. <16 years) have an increased risk of adverse pregnancy outcomes.