Adolescent pregnancy exerts negative physiological and psychological influences on adolescent girls undergoing unique physical and mental development. Adolescent pregnancy is currently a critical public health concern for governments worldwide. This study introduces the physical and mental development characteristics of adolescents and describes the current sexual behavior among adolescents in Taiwan. A literature review is conducted to investigate the physiological, psychological, and social impacts of adolescent pregnancy, such as the health effects on the adolescent mothers, low birthweight, school dropouts, economic challenges, stress in role adjustment, and lack of support systems. Subsequently, the factors affecting the decision-making process of pregnant adolescents are explored.