Abstract： Objective:To analyze the impact of adolescent pregnancy on maternal and infant outcomes.Methods:A retrospective cohort study was conducted on 5 765 parturbirths in Jining Medical College Hospital from January 1, 2019 to December 31, 2020. The parturbirths were divided into adolescent group (maternal age<20 years, 280 cases), age group 1 (maternal age 20-24 years, 1 733 cases) and age groups 2 (maternal age 25-34 years, 3 752 cases). All information was collected through the hospital′s electronic case system. General data, pregnancy characteristics and outcomes were compared among the three groups by analysis of variance (ANOVA), χ 2 tests and binary logistics regression analysis was used to analyze the impact of adolescent pregnancy on maternal and infant outcomes. Results:In the adolescent group, the proportion of women with an education of junior high school or below, rural residence, no fixed income, unmarried, and no history of induced abortion were all significantly higher than those in age group 1 and age group 2 (82.50% vs 17.37%, 14.37%; 59.29% vs 42.70%, 43.36%; 80.71% vs 15.52%, 14.71%; 75.71% vs 12.23%, 9.97%; 82.50% vs 71.84%, 71.91%) (all P<0.05); there was no significant differences in age at menarche, body mass index before pregnancy, and weight gain during pregnancy among the three groups (all P>0.05). The proportion of preterm birth, low birth weight infants and transferring to neonatal intensive care unit (NICU) in the adolescent group were all significantly higher than those in age group 1 and age group 2 (5.36% vs 1.10%, 1.57%; 5.00% vs 0.23%, 0.05%; 21.79% vs 6.12%, 15.17%); the incidence of anemia in pregnancy in the adolescent group was significantly higher than that in age group 1 (15.36% vs 9.75%), and the incidence of postpartum hemorrhage was significantly higher than that in the age group 2 (10.71% vs 6.08%). The incidence of failed vaginal trials leading to cesarean section, amniotic fluid contamination, and episiotomy was significantly lower in the adolescent group than those in age group 2 (8.57% vs 15.22%, 10.71% vs 18.10%, 33.95% vs 40.01%) (all P<0.05). The incidence of failed vaginal trials leading to cesarean section was inversely associated with gestational age (adolescent group, OR=0.252, 95% CI: 0.123-0.515; age group 1, OR=0.673, 95% CI: 0.567-0.799) (both P<0.05); the risks of low birth weight infants (adolescent group, OR=7.440, 95% CI: 3.426-16.156; age group 1, OR=0.103, 95% CI: 0.032-0.330) and transferring to the NICU (adolescent group, OR=1.661, 95% CI: 1.120-2.463; age group 1, OR=0.360, 95% CI: 0.290-0.448) showed a U-shaped distribution in different pregnancy age groups, they were both higher in the adolescent group than those in the age group 2 (both P<0.05); the risk of episiotomy (adolescent group, OR=0.002, 95% CI: 0-0.016; age group 1, OR=1.308, 95% CI: 1.151-1.485) showed an inverted U-shape distribution across the different pregnancy age groups, it was lower in the adolescent group than that in age group 2 (both P<0.05). Conclusion:Adolescent pregnancy is associated with a lower risk of conversion to cesarean section and episiotomy due to failed vaginal delivery, but may increase the risk of low birth weight infants and transferring to NICU.