Stubbornly high pregnancy prevalence in adolescent females worldwide, results in numerous adverse pregnancy outcomes, causing wide public concern. Thereby, it is pressing to study the pregnancy characteristics, adverse pregnancy outcomes and associated factors in adolescent primiparous females.

To examine adverse pregnancy outcomes and related factors in adolescent primiparous females via comparing pregnancy outcomes of them with those of emerging and early adult females.

Primiparous females (n=12 222, <35 year old) with ≥28 weeks of gestation were recruited from Ningbo Women and Children's Hospital during 2019—2020, including 210 aged 13-19 (adolescent group) , 1 729 aged 20-24 (adult group 1) , and 10 283 aged 25-34 (adult group 2) . Data were collected for maternal demographics, pregnancy complications, comorbidities, delivery course and adverse fetal outcomes. The associations of age, marital status, education background, rural or urban living, income, body mass index (BMI) with adverse maternal and fetal outcomes were analyzed.

Adolescent primiparas had higher proportions of individuals with unmarried status, junior high school or lower education level, rural living, and an unstable income, as well as less mean prenatal care visits than the other two groups (P<0.05) . Moreover, adolescent primiparas also had higher rates of placental abruption, maternal anemia, vaginal delivery, perineal laceration, premature labor, (very) low-birth-weight infant, and stillbirth (P<0.05) . Multivariate Logistic regression analysis demonstrated that in adolescent primiparas, 13-24 years, unmarried and BMI<18.5 kg/m² were associated with lower risk of gestational diabetes (P<0.05) ; gravida≥3 and BMI≥28 kg/m² were risk factors for gestational diabetes (P<0.05) ; 13-24 years, unmarried, unstable income and BMI≥28 kg/m² were risk factors for vaginitis (P<0.05) ; 13-19 year-old, unmarried, junior high school or lower education level and unstable income were risk factors for placental abruption (P<0.05) ; gravida≥3 was the risk factor for placenta previa (P<0.05) ; 13-24 years, unmarried, junior high school or lower education level, rural living and unstable income were risk factors for maternal anemia (P<0.05) ; BMI≥28.0 kg/m² was associated with lower risk of maternal anemia (P<0.05) . Further analysis showed that 13-24 years, unmarried, junior high school or lower education level, rural living and BMI<18.5 kg/m², were associated with higher possibility of having vaginal delivery (P<0.05) , whereas gravida≥3 was associated with higher possibility of having cesarean section (P<0.05) . Aged 13-19 years, unmarried, junior high school or lower education level, unstable income, gravida≥3, and BMI<18.5 kg/m² or ≥28.0 kg/m² were risk factors for premature labor (P<0.05) . Aged 13-19 year-old, unmarried, junior high school or lower education level, rural living, unstable income, gravida≥3, and BMI<18.5 kg/m² were risk factors for (very) low-birth-weight infants (P<0.05) . 20-24 year-old was associated with lower risk of fetal distress (P<0.05) . 13-19 year-old and unmarried were risk factors for stillbirth (P<0.05) . 13-24 years, junior high school or lower education level, rural living, unstable income, and gravida≥3 were risk factors for neonatal asphyxia (P<0.05) .

Adolescent primiparous females were featured by high rates of having unmarried status, rural living, an unstable income, low education level, fewer prenatal care visits, and adverse pregnancy outcomes. Younger age, unmarried, poor socioeconomic status, higher number of pregnancies, and excessive low or high BMI were risk factors for adverse pregnancy outcomes in this group. Healthcare specialists should schedule prenatal examinations for these people based on the high risk factors accordingly. And government at all levels and affiliated adolescent institutions should offer appropriate social and economic support for teenage mothers to reduce adverse pregnancy outcomes.