Background The escalating global concern over increased body weight in adolescents, coupled with the rising rates of adolescent pregnancy worldwide, presents a significant challenge to healthcare systems. We plan to identify the maternal and neonatal consequences associated with pre-pregnancy overweight in adolescent women. Methods Throughout five years, all singleton adolescent pregnant women with pre-pregnancy self-reported body mass index (BMI) of 18.5– ≤ 29.9 were involved during the first-trimester visit. Two groups were generated: overweight and appropriate-weight (BMI 25–29.9 and 18.5–24.9, respectively). Obstetric and neonatal outcomes were observed prospectively and statistically adjusted for the confounding factors. Results The overweight group (223 women) had significantly higher pregnancy weight gain, birth weight, and gestational age than the appropriate-weight group (621 women). Most obstetric outcomes occurred significantly in overweight women like primary Cesarean section (CS) [odds ratio (OR) (95%confidence interval (CI)) = 1.5 (1.06–2.2)], cephalopelvic disproportion [OR (95% CI) = 1.3 (1.1–1.8)], labor induction [OR (95% CI) = 1.2 (1.09–2.3)]. Regarding neonatal outcomes, macrosomia [OR (95% CI) = 1.6 (1.3–2.7)] and non-reassuring fetal status (NRFS) [OR (95% CI) = 1.1(1.0–1.7)] had higher statistical significance in overweight women. Oppositely, small for gestational age [OR (95% CI) = 0.7(0.4–0.9)] and low birth weight [OR (95% CI) = 0.5(0.3–0.8)] were more frequent in appropriate-weight women. Conclusion Overweight adolescent pregnant women exhibited significantly higher percentages of obstetrical outcomes, like as primary CS, failure to progress, labor induction, postdate delivery, gestational diabetes, and gestational hypertension. Additionally, elevated rates of neonatal complications were found, including macrosomia and NRFS.