This study sought to estimate the prevalence and distribution of newborns to mothers under age 18 in Ecuador and the association between perinatal indicators and maternal marital status. Newborn records obtained from Ecuador's Instituto Nacional de Estadísticas y Censos (INEC) between 2015 and 2020 were used to assess the joint association between maternal age groups (10-15, 16-17, 18-19, and 20-24 years) and marital status (married, common-law, and single) with low birthweight, preterm birth, and inadequate prenatal care. The prevalence of newborns to mothers under age 18 was 9.3% overall, but declined over the study period, drastically among married mothers. The association between marital status and perinatal indicators depended on maternal age. The more favorable outcomes observed among married mothers aged 20-24 years (compared to their single counterparts) weaken or disappear among mothers under age 18. Mothers in stable unions exhibited outcomes in between those of married and single mothers.