AbstractObesity is an important issue among fertile women as it may affect obstetric and neonatal outcomes.Obstetric and neonatal outcomes of primiparous women were retrospectively analyzed in non-obese (n=11387) and obese (n=943) women. A subgroup analysis was performed in obese women divided into three groups: Grade I obesity (Group A, n=654), Grade II obesity (Group B, n=192), and Grade III obesity (Group C, n=97). Odds ratios (OR) were expressed with the corresponding 95% confidence intervals (CI).The incidence of gestational diabetes (non-obese, 1.9%; obese, 7.6%; Group C, 19.6%) and preeclampsia (non-obese, 3.3%; obese, 13.5%; Group C, 17.5%) increased with rising weight. The risk of non-elective cesarean section was significantly higher in obese women than in non-obese women (21.7% vs. 13.2%). The risk of extreme preterm birth (before 28 weeks of gestation) doubled in the Grade I obesity group (OR, 2.1; 95% CI, 1.4–3.2) and nearly tripled in women with body mass index ≥35 kg/mPre-pregnancy obesity is associated with higher incidences of gestational diabetes and preeclampsia. Our study shows that obese women have a higher risk of non-elective cesarean section and preterm birth.