Objective. Maternal lifestyle factors are potential predictors of pregnancy complications. We examined relations between modifiable factors and delivery complications. Design. Prospective cohort. Setting. University hospital antenatal clinic, Oslo, Norway. Sample. A cohort of 553 women followed through pregnancy and delivery. Main outcome measures. Pre-specified birth complications: cesarean section (CS), operative vaginal deliveries (VDs), third and fourth degree of perineal lacerations and hemorrhage (≥1,000 ml). Methods. Univariate and multiple logistic regression analyses were performed. Besides high birthweight (≥4,200 g), modifiable predictors (high body mass index (BMI), fasting glucose and physical inactivity) and non-modifiable predictors (parity, maternal age, gestational age, and gender) were considered. Results. Significant predictors for induction of labor were parity (odds ratio (OR): 2.1; 95% CI 1.3–3.5), maternal age (OR: 2.0; 1.2–3.4), gestational age (OR: 1.9; 1.1–3.1), and BMI ≥30 (OR: 4.2; 2.2–7.8, p<0.01). High birthweight and high BMI were overrepresented among CSs. Emergency CS was associated with birthweight (OR: 3.7; 1.7–8.1), parity (OR: 3.5; 1.7–7.2), maternal age (OR: 2.6; 1.3–5.3), and induction of labor (OR: 4.8; 2.6–9.1). After excluding CS, operative VD was associated with parity (OR: 8.7; 3.8–20) and gender (OR: 2.2; 1.2–14.1). Perineal laceration was associated with pre-gestational physical inactivity (OR: 6.1; 1.6–22.9) and operative VD (OR: 5.1; 1.5–17.6). Hemorrhage was associated with high birthweight (OR: 4.2; 1.2–4.7) and BMI ≥30 (OR: 4.6; 1.2–17.7). Conclusions. Pre-gestational physical inactivity increased the risk of perineal lacerations and male infants were associated with higher risk of vaginal operative delivery.