Background: There are so many studies with controversial results focusing on pregnancy outcomes in adolescents. Gynecologic age (GA)- the time between menarche and chronological age at the first pregnancy- has been considered as a physiological maturity indicator with a lower GA assumed as a risk factor for pregnancy outcomes in adolescents. The present study aimed to investigate the relationship between GA and maternal/fetal weight gain in adolescent pregnancies. Methods: This is an analytical study in which 275 primiparous women aged 20 to 29 years, were compared with two groups of adolescent women: GA ≤3 (n=141) and GA >3 years (n=131) in terms of weight gain during pregnancy, anemia and birth weight of newborns. All women were married and had been admitted to the health centers of two cities in south west Iran in 2017. Results: Inadequate/excessive weight gain in adolescents who had a GA≤3 was significantly more than that in adult group (p=0.04). There was no significant difference among three groups in terms of anemia and birth weight (p> 0.05). Conclusion: The association was revealed only between the GA≤3 years and increased risk of undesirable weight gain. Including only married adolescents, is the main difference between this study and other studies.