Introduction: Adolescent pregnancies are associated with adverse maternal and fetal outcomes including preeclampsia, preterm birth, and fetal growth restriction compared to adult pregnancies. The purpose of our study is to compare the incidents of obstetric outcomes between the adolescent pregnancies and adult pregnancies. Materials and methods: This retrospective case-control study was conducted between January 2013 and January 2018 at Kanuni Sultan Suleyman Research and Training Hospital, Istanbul, Turkey. The institutions' medical records were screened for women with pregnancies after 24 weeks of gestation. Women under 19 years of age were included as the adolescent group and women between the ages of 20 and 29 were included as the control group. Obstetric outcomes were compared between the groups. Results: There were 3875 adolescent pregnancies in the case group and 3875 adult pregnancies in the control group. Even after adjusting for confounders in our adolescent pregnant cohort, the odds of intrauterine growth restriction, preterm birth and premature rupture of membranes were higher than in our adult pregnant cohort. On the other hand, we found low incidents of preeclampsia and gestational diabetes mellitus in pregnant women younger than 19 years of age. Conclusions: Adolescent pregnancies should be closely followed up as they have higher preterm birth rates as well as the risk of intrauterine growth restriction.