Abstract Adolescent pregnancy is associated with adverse birth outcomes. However, the determinants of these outcomes are understudied. The present study sought to identify the predictors of adverse birth outcomes among pregnant adolescents in Ghana. In this prospective health centre-based study, 416 pregnant adolescents, aged 13–19 years old, were followed, and 270 birth outcomes were evaluated. We collected data on socio-demographic variables, eating behaviour, household hunger scale (HHS), lived poverty index (LPI) and compliance to antenatal interventions. The prevalence of low birth weight (LBW) and preterm births (PTB) were 15⋅2 and 12⋅5 %, respectively. Pregnant adolescents with no formal education (AOR 9⋅0; P = 0⋅004; 95 % CI 2⋅1, 39⋅8), those who experienced illness (AOR 3⋅0; P = 0⋅011; 95 % CI 1⋅3, 7⋅0), those who experienced hunger (OR 2⋅9; P = 0⋅010; 95 % CI 1⋅3, 6⋅5) and those with high LPI (OR 2⋅5; P = 0⋅014; 95 % CI 1⋅2, 5⋅3) presented increased odds of delivering preterm babies compared with those who have had secondary education, did not experience any illness, were not hungry or having low LPI, respectively. Pregnant adolescents who used insecticide-treated net (ITN) (AOR 0⋅4; P = 0⋅013; 95 % CI 0⋅2, 0⋅9) presented reduced odds LBW children; while those who experienced illness (AOR 2⋅7; P = 0⋅020; 95 % CI 1⋅2, 6⋅0), poorer pregnant adolescents (OR 2⋅5; P = 0⋅014; 95 % CI 1⋅1, 4⋅8) and those who experienced hunger (AOR 3⋅0; P = 0⋅028; 95 % CI 1⋅1, 8⋅1) presented increased odds of LBW children compared with those who used ITN, were not ill, were not poor or did not experience hunger. Adverse birth outcomes were associated with ANC compliance and socioeconomic factors of the pregnant adolescents. Hence, strengthening antenatal uptake and compliance by pregnant adolescents, promoting their livelihood and socioeconomic status, and interventions to prevent teenage pregnancies are strongly recommended.